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  • 1
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Physics Letters B 294 (1992), S. 466-478 
    ISSN: 0370-2693
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Physics Letters B 317 (1993), S. 474-484 
    ISSN: 0370-2693
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
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  • 3
    Publication Date: 2016-07-13
    Description: During the last centuries, populations of marine megafauna—such as seabirds, turtles, and mammals—were intensively exploited. At present, other threats such as bycatch and pollution affect these species, which play key ecological roles in marine ecosystems as apex consumers and/or nutrient transporters. This study analyses the distribution of six megafaunal species ( Chelonia mydas , Caretta caretta , Dermochelys coriacea , Thalassarche melanophris , Otaria flavescens , and Arctocephalus australis ) coexisting in the Southwestern Atlantic to discuss their protection in terms of current management strategies in the region. Through the prediction of the species potential distributions and their relation to bathymetry, sea temperature and oceanographic fronts, key ecological areas are defined from a multi-taxa perspective. Information on the distribution of 70 individuals (18 sea turtles, 19 albatrosses, and 33 otariids) was obtained through satellite tracking conducted during 2007–2013 and analysed using a Geographic Information System and maximum entropy models. During the autumn–winter period, megafaunal species were distributed over the continental shelves of Argentina, Uruguay, and Brazil, mainly over the Argentine Exclusive Economic Zone and the Argentina-Uruguay Common Fishing Zone. Despite some differences, all megafaunal species seems to have similar environmental requirements during the autumn–winter period. Mostly waters shallower than 50 m were identified as key ecological areas, with the Río de la Plata as the habitat with the highest suitability for all the species. This area is highly productive and sustains the main coastal fisheries of Uruguay and Argentina, yet its role as a key ecological area for megafaunal species has been underestimated until now. This approach provides a basis to analyse the effect of anthropic activities on megafaunal species through risk maps and, ultimately, to generate knowledge to improve national and bi-national management plans between Argentina and Uruguay.
    Print ISSN: 1054-3139
    Electronic ISSN: 1095-9289
    Topics: Biology , Geosciences , Physics
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  • 4
    Publication Date: 2016-07-13
    Description: In the North Sea flatfish fishery, electric pulse trawls have been introduced to replace the conventional mechanical method. Pulse trawls reduce the fuel consumption, reduce adverse impact on the ecosystem but cause injuries in gadoids. We describe the design and electrical properties of pulse trawls currently in use and study the behavioural response and injuries in cod exposed to electrical pulses under controlled conditions. Pulse trawls operate at an average power of 0.7 kW m –1 beam length and a duty cycle of ~2%. The electric field is heterogeneous with highest field strength occurring close to the conductors. Cod were exposed to three different pulse types for a range of field strengths, frequencies, and duty cycles. Two size classes were tested representing cod that escape through the meshes (11–17 cm) and market-sized cod that are retained in the net (34–56 cm). Cod exposed to a field strength of ≥37 V m –1 responded by moderate-to-strong muscular contractions. Some of the large cod ( n = 260) developed haemorrhages and fractures in the spine, and haemal and neural arches in the tail part of the body. The probability of injuries increased with field strength and decreased when frequency was increased from 100 to 180 Hz. None of the small cod ( n = 132) were injured and all survived. The field strength at the lateral boundaries of the trawl was too low to inflict injuries in cod.
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  • 5
    Publication Date: 2016-07-13
    Description: A coupled biophysical model is used to explore the physical controls involved in the timing of the spring phytoplankton bloom in fjords. Observations from Rivers Inlet, British Columbia, are used to force and evaluate the model. It is found that the interannual variation in timing is due primarily to variations in retention, in particular, to variations in horizontal advection out of the fjord. The two dominant processes are (i) strong outflow winds rapidly advecting the surface layer and thus the phytoplankton population out of the fjord and (ii) losses due to high river flux increasing the estuarine circulation. Both processes delay the timing of spring bloom. Smaller effects on the interannual variation are due to increased wind mixing which deepens the mixing layer and reduces light to phytoplankton, and increased river flow which increases the stratification and decreases the mixing layer depth. Observed interannual variations in cloudiness were small. Strong outflow winds are common in winter along the British Columbia coast, but generally cease after the spring wind transition. Thus, observed interdecadal variations in the spring transition date probably imply strong variations in the timing of spring phytoplankton blooms in British Columbia fjords.
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  • 6
    Publication Date: 2016-07-13
    Description: Since "balanced harvest" was proposed in 2010 as a possible tool in the operationalization of the ecosystem approach to fisheries (EAF), the concept gained extensive international attention. Because maintaining ecosystem structure and achieving maximum sustainable yields have become two of the key international legal obligations in fisheries management, balanced harvest is as topical as ever. An international workshop on balanced harvest, organized by the IUCN Fisheries Expert Group at FAO headquarters in 2014, reviewed the progress in the field and discussed its prospects and challenges. Several articles in this theme set, mostly based on presentations from the workshop, discuss ecological, economical, legal, social, and operational issues surrounding the key management goals. Progress is being made on understanding of the theoretical underpinnings of balanced harvest and its practical feasibility. Yet, a basic debate on the concept of balanced harvest continues. To move the EAF forward, we anticipate and encourage further research and discussion on balanced harvest and similar ideas.
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  • 7
    Publication Date: 2016-07-13
    Description: Sampling of euphausiids is difficult because of their intermediate size between macrozooplankton and micronekton. The Barents Sea is one of the few marine areas where there have been long-term studies of euphausiids. We have examined three monitoring datasets on euphausiids and consider likely sources of errors associated with the sampling. Results indicated a high degree of patchiness in the distribution of euphausiids, even at the largest scale of sampling with a pelagic trawl. This indicates that euphausiids may occur in large, but infrequent, swarms that have a low probability of being sampled by small nets. The mean biomass of euphausiids sampled with MOCNESS was 2 g wet weight m –2 integrated over the water column, which is an underestimate due to avoidance of large individuals. The mean biomass obtained with pelagic trawl in the upper 60 m of water at night during an autumn survey was 10 g wet weight m –2 . The plankton net on bottom trawl collected mean and median density of euphausiids (0.1–0.2 g wet weight m –3 ) near bottom during a winter survey similar to the values found with pelagic trawl in the upper layer during autumn. The mean density for the autumn survey showed an increase from 2000 to 2011, while the winter survey showed generally a decrease from 2000–2007 to 2011. The increase in the autumn series coincided with a general warming trend presumably with a larger influx of euphausiids with Atlantic water, notably of Meganyctiphanes norvegica . In contrast, the decline during winter may reflect a decrease, particularly of Thysanoessa raschii in the southeastern Barents Sea in the most recent years. Improvements in sampling gears combined with more and better use of acoustical and optical technologies offer great promise for improved monitoring and quantification of the roles of euphausiids in the Barents Sea ecosystem.
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  • 8
    Publication Date: 2016-07-13
    Description: Balanced fishing proposes a considerable change to current fisheries management to increase overall biomass harvested while reducing the ecosystem impacts of large-scale fisheries. However, to date, the work to a large degree has focused on simplified models, which exclude much of the variability in real ecosystems, as well as basing harvesting rates on a perfect, but unrealistic, knowledge on stock productivity. Furthermore, the published studies have avoided examining the practicalities of implementing balanced fishing in a real world. This has resulted in a gap that remains to be overcome before balanced fishing can be considered a viable management strategy for large marine ecosystems. We discuss variability in recruitment, in biology and life history characteristics, in data quality, and in fishing practice and management, and their implications for implementation of balanced fishing, using examples from the Barents Sea. We try to outline the complexities that need to be investigated as a precursor to moving balanced fishing from an academic exercise to a practical management scheme. Given the difficulties in moving to "full" balanced fishing, we highlight the importance of investigating to what extent benefits can be gained by implementing only the most achievable parts of a balanced fishing regime.
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  • 9
    Publication Date: 2016-07-13
    Description: European eel ( Anguilla anguilla ) is considered as critical endangered and even under the best circumstances it may take decades before the stock recovers. Estimation of eel escapement biomass, B escapement , is of critical importance to evaluate management schemes and to predict the recovery potential for the eel stock. Westerberg and Wickström (2015. Stock assessment of eels in the Baltic: reconciling survey estimates to achieve quantitative analysis. ICES Journal of Marine Science, 73: 75–83) attempt to estimate potential B escapement based on the assumptions that all elvers at the entrance of the Baltic also migrate into the Baltic Sea and that natural mortality is low under the whole growth stage (close to 0.02 at the age of 10 years and older). As a consequence, Westerberg and Wickström estimated the present potential B escapement at ~10–20 000 tonnes and fishing mortality close to 0.05–0.10, while it was also suggested that other sources of anthropogenic mortality may reduce the actual escapement to unknown levels. Here we argue that these conclusions are entirely speculative and contradicted by tagging experiment and fishery data, which instead indicate a much higher fishing mortality (mortality induced by legal professional fishery) rates and a considerably smaller eel biomass.
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  • 10
    Publication Date: 2016-07-13
    Description: Discard bans have been proposed as part of management policies aimed at balanced harvest (BH). Nationwide discard bans exist in several countries, including Chile, the European Union, Norway, and New Zealand. We analysed experiences from these countries to determine whether or not discard bans are in contradiction with BH, based on six aspects: policy objectives, species/sizes applicability, accompanying technical measures, at-sea monitoring and control, and possible impacts. When discard bans are fully implemented, fishing operations change to more selective fishing, typically targeting bigger individuals of main commercial species. This is consistent with the primary objective of many discard policies, i.e. to reduce unwanted catch. In contrast, proponents of BH argue that broader catch diversity, a product of a widespread harvest strategy, should be sought to avoid major impacts on the ecosystem. Our analysis demonstrates that the scope of discard bans is often limited to main commercial species, although usually they can be extended to include more ecosystem components. Some of the policies examined also prohibit the use of unwanted catches for human consumption, thus limiting their effective use. However, the implementation of discard bans requires high levels of at-sea monitoring and effective control, and/or strong incentives to fish more selectively, neither of which applied in most cases examined. We conclude that if discard bans were set differently, they could contribute to fishery management policies aiming at BH. Their goals should be in line with BH, i.e. to reach a wider global harvest pattern, or at least be established within management regimes that promote high compliance. Finally, the extent to which a discard ban contributes to achieve BH depends also on the relative importance of the ecosystem benthic and megafauna components.
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  • 11
    Publication Date: 2016-07-13
    Description: Using a large dataset of US offices we analyse the relationship between investors’ distance to their assets and the effective rent of these assets, and study the extent to which property managers can influence this relationship. We construct hedonic rent models to control for other known rent determinants. It turns out that proximity matters: holding everything else constant, investors located closely to their office buildings are able to extract significantly higher effective rents from these assets, especially if these buildings are of low quality. This effect is due to significant differences in occupancy levels. Interestingly, property managers can affect this relationship, mitigating the adverse effects of investor distance on effective office rents. Especially if the owner does not reside in the same state as the building, external property management is of importance, most prominently so for class-B office buildings.
    Keywords: G11 - Portfolio Choice ; Investment Decisions, R12 - Size and Spatial Distributions of Regional Economic Activity, R32 - Other Production and Pricing Analysis, R33 - Nonagricultural and Nonresidential Real Estate Markets
    Print ISSN: 1468-2702
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    Topics: Geography , Economics
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  • 12
    Publication Date: 2016-07-13
    Description: This article draws on extensive fieldwork conducted in Central Asia to explore food exports to Russia. It takes its theoretical starting point in global value chain theory and pinpoints chain entry barriers relating to financing, transportation and standards. The article also proposes rethinking the aspects of territoriality and institutional context, and suggests their integration into one concept, or rather a process of contextualizing territories. In doing so, the article argues for a methodology that not only examines current events, but also captures change as particularly important in what we term the territory in transition examined here.
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  • 13
    Publication Date: 2016-07-13
    Description: This article proposes a quantitative analysis of the interdependencies between port specialization and regional specialization across the world. A global database is elaborated, covering about 360 port regions in both developed and developing countries. One goal is to verify how interdependent port traffic and regional characteristics are, in a context of increasingly flexible commodity and value chains. Despite the aggregated dimension of available data and the heterogeneity of local situations, the main results confirm the affinity between the primary sector and raw materials traffic, and between the tertiary sector and general cargo traffic, whereas the industrial sector offers mixed evidence. This allows us to address fundamental questions raised by both economic geography and regional science about transport and local development. The global typology of port regions points to certain regularities in their spatial distribution, and the article discusses the policy implications of particular cases.
    Keywords: L90 - General, O18 - Regional, Urban, and Rural Analyses, R40 - General
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  • 14
    Publication Date: 2016-07-13
    Description: This article examines various upgrading and downgrading repositioning firm strategies within global value chains (GVCs) or global production networks (GPNs). It builds upon recent evidence that the mode of governance could vary profoundly among firms engaged in the same GVC/GPN. Therefore, the relevance of particular types of upgrading that were originally derived from the ideal types of GVC/GPN governance will be reconsidered. It is argued that the existing dissonance in the literature over possibilities for functional upgrading can be attributed to the different modes of governance that can exist within a particular GVC/GPN and to the diverse nature of functional upgrading. Consequently, a typology of functional upgrading is outlined, and it is argued that these different types vary significantly according to their probability and potential risk-benefit ratios. The article also introduces passive, adaptive and strategic downgrading and outlines their potential negative and positive effects on firms.
    Keywords: F63 - Economic Development, L23 - Organization of Production, L60 - General
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  • 15
    Publication Date: 2016-07-13
    Description: As nations continue to grapple with growing infrastructure demand, financial markets will play an increasingly prominent role in the landscape for urban infrastructure. Yet existing literature tends to depict the ‘financialization’ of urban infrastructure assets as a restless move towards market efficiency aided by the growing transparency of financial information. This article offers a different view, showing how the spatial richness of financial data for infrastructure has progressed towards what we term a more permanent state of ‘informational translucency’. We draw on 53 interviews with participants in the market for infrastructure investment to present this more complicated picture of infrastructure finance, thereby elaborating a more granular understanding of how information flows through and shapes financial market geography. From this we propose a relational model that contributes to theoretical understandings of how financial products are intermediated over time and space.
    Keywords: O18 - Regional, Urban, and Rural Analyses
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  • 16
    Publication Date: 2016-07-13
    Description: This article extends research exploring progressive models of reproducing economic life by reporting on research into some of the infrastructure, practices and motivations for Islamic charitable giving in London. In so doing the article: (i) makes visible sets of values, practices and institutions usually hidden in an otherwise widely researched international financial centre; (ii) identifies multiple, hard-to-research civic actors who are mobilising diverse resources to address economic hardship and development needs; and (iii) considers how these charitable values, practices and agents contribute to contemporary thinking about progressive economic possibilities.
    Keywords: D14 - Personal Finance, O12 - Microeconomic Analyses of Economic Development
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  • 17
    Publication Date: 2016-07-13
    Description: We estimate the impact of drug cartels and drug-related homicides on crime and perceptions of security in Mexico. Since the location where drug cartels operate might be endogenous, we combine the difference-in-difference estimator with instrumental variables. Using surveys on crime victimization we find that people living in areas that experienced drug-related homicides are more likely to take extra security precautions. Yet, these areas are also more likely to experience certain crimes, particularly thefts and extortions. In contrast, these crimes and perceptions of insecurity do not change in areas where cartels operate without leading to drug-related homicides.
    Keywords: C26 - Instrumental Variables (IV) Estimation, K49 - Other, R59 - Other
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  • 18
    Publication Date: 2016-07-13
    Description: The motion of superfluid vortices in a neutron star crust is at the heart of most theories of pulsar glitches. Pinning of vortices to ions can decouple the superfluid from the crust and create a reservoir of angular momentum. Sudden large-scale unpinning can lead to an observable glitch. In this paper, we investigate the scattering of a free vortex off a pinning potential and calculate its mean free path, in order to assess whether unpinned vortices can skip multiple pinning sites and come close enough to their neighbours to trigger avalanches, or whether they simply hop from one pinning site to its neighbour, giving rise to a more gradual creep. We find that there is a significant range of parameter space in which avalanches can be triggered, thus supporting the hypothesis that they may lie at the origin of pulsar glitches. For realistic values of the pinning force and superfluid drag parameters, we find that avalanches are more likely in the higher density regions of the crust where pinning is stronger. Physical differences in stellar parameters, such as mass and temperature, may lead to a switch between creep-like motion and avalanches, explaining the different characteristics of glitching pulsars.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
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  • 19
    Publication Date: 2016-07-13
    Description: We present the results of the application of locally linear embedding (LLE) to reduce the dimensionality of dereddened and continuum subtracted near-infrared spectra using a combination of models and real spectra of massive protostars selected from the Red MSX Source survey data base. A brief comparison is also made with two other dimension reduction techniques; principal component analysis (PCA) and Isomap using the same set of spectra as well as a more advanced form of LLE, Hessian locally linear embedding. We find that whilst LLE certainly has its limitations, it significantly outperforms both PCA and Isomap in classification of spectra based on the presence/absence of emission lines and provides a valuable tool for classification and analysis of large spectral data sets.
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  • 20
    Publication Date: 2016-07-13
    Description: The past decade and a half has seen the design and execution of several ground-based spectroscopic surveys, both Galactic and Extragalactic. Additionally, new surveys are being designed that extend the boundaries of current surveys. In this context, many important considerations must be done when designing a spectrograph for the future. Among these is the determination of the optimum wavelength coverage. In this work, we present a new code for determining the wavelength ranges that provide the optimal amount of information to achieve the required science goals for a given survey. In its first mode, it utilizes a user-defined list of spectral features to compute a figure-of-merit for different spectral configurations. The second mode utilizes a set of flux-calibrated spectra, determining the spectral regions that show the largest differences among the spectra. Our algorithm is easily adaptable for any set of science requirements and any spectrograph design. We apply the algorithm to several examples, including 4MOST, showing the method yields important design constraints to the wavelength regions.
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  • 21
    Publication Date: 2016-07-13
    Description: We reconstruct the projected mass distribution of a massive merging Hubble Frontier Fields cluster MACSJ0416 using the genetic algorithm based free-form technique called Grale. The reconstructions are constrained by 149 lensed images identified by Jauzac et al. using HFF data. No information about cluster galaxies or light is used, which makes our reconstruction unique in this regard. Using visual inspection of the maps, as well as galaxy-mass correlation functions we conclude that overall light does follow mass. Furthermore, the fact that brighter galaxies are more strongly clustered with mass is an important confirmation of the standard biasing scenario in galaxy clusters. On the smallest scales, approximately less than a few arcseconds, the resolution afforded by 149 images is still not sufficient to confirm or rule out galaxy-mass offsets of the kind observed in ACO 3827. We also compare the mass maps of MACSJ0416 obtained by three different groups: Grale, and two parametric Lenstool reconstructions from the CATS and Sharon/Johnson teams. Overall, the three agree well; one interesting discrepancy between Grale and Lenstool galaxy-mass correlation functions occurs on scales of tens of kpc and may suggest that cluster galaxies are more biased tracers of mass than parametric methods generally assume.
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  • 22
    Publication Date: 2016-07-15
    Description: We have monitored the massive binary star Carinae with the CTIO/Small and Moderate Aperture Research Telescope System 1.5 m telescope and CHIRON spectrograph from the previous apastron passage of the system through the recent 2014.6 periastron passage. Our monitoring has resulted in a large, homogeneous data set with an unprecedented time-sampling, spectral resolving power, and signal to noise. This allowed us to investigate temporal variability previously unexplored in the system and discover a kinematic structure in the P Cygni absorption troughs of neutral helium wind lines. The features observed occurred prior to the periastron passage and are seen as we look through the trailing arm of the wind–wind collision shock cone. We show that the bulk of the variability is repeatable across the last five periastron passages, and that the absorption occurs in the inner 230 au of the system. In addition, we found an additional, high-velocity absorption component superimposed on the P Cygni absorption troughs that has been previously unobserved in these lines, but which bears resemblance to the observations of the He i 10830 Å feature across previous cycles. Through a comparison of the current smoothed particle hydrodynamical simulations, we show that the observed variations are likely caused by instabilities in the wind–wind collision region in our line of sight, coupled with stochastic variability related to clumping in the winds.
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  • 23
    Publication Date: 2016-07-15
    Description: We investigated the typical environment and physical properties of ‘red discs’ and ‘blue bulges’, comparing those to the ‘normal’ objects in the blue cloud and red sequence. Our sample is composed of cluster members and field galaxies at z ≤ 0.1, so that we can assess the impact of the local and global environment. We find that disc galaxies display a strong dependence on environment, becoming redder for higher densities. This effect is more pronounced for objects within the virial radius, being also strong related to the stellar mass. We find that local and global environment affect galaxy properties, but the most effective parameter is stellar mass. We find evidence for a scenario where ‘blue discs’ are transformed into ‘red discs’ as they grow in mass and move to the inner parts of clusters. From the metallicity differences of red and blue discs, and the analysis of their star formation histories, we suggest the quenching process is slow. We estimate a quenching time-scale of ~2–3 Gyr. We also find from the sSFR– M * plane that ‘red discs’ gradually change as they move into clusters. The ‘blue bulges’ have many similar properties than ‘blue discs’, but some of the former show strong signs of asymmetry. The high asymmetry ‘blue bulges’ display enhanced recent star formation compared to their regular counterparts. That indicates some of these systems may have increased their star formation due to mergers. None the less, there may not be a single evolutionary path for these blue early-type objects.
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  • 24
    Publication Date: 2016-07-15
    Description: We study the dependence of the estimated size and geometry of the medium on the time-averaged spectral model assumed and on the frequency of the kHz quasi-periodic oscillation (QPO) in the framework of a thermal Comptonization model. We use the high-quality time lag and rms obtained during 1996 March 3 observation of 4U 1608–52 by RXTE as well as other observations of the source at different QPO frequencies where a single time lag between two broad energy bands has been reported. We compare the results obtained when assuming that the time-averaged spectra are represented by the spectrally degenerate ‘hot ( kT b ≥ 1 keV)’ and ‘cold ( kT b ≤ 0.5 keV)’ seed spectral models where T b is seed source temperature. We find that for the ‘hot-seed’ model the medium size is in the range of 0.3–2.0 km and the size decreases with increasing QPO frequency. On the other hand, for the ‘cold-seed’ model, the range for the sizes is much larger 0.5–20 km and hence perhaps show no variation with QPO frequency. Our results emphasize the need for broad-band spectral information combined with high-frequency timing to lift this degeneracy. We further compare the rms as a function of energy for the upper kHz QPO, and indeed we find that the driver for this QPO should be temperature variations of the corona identical to the lower kHz QPO. However, the time lag reported for the upper kHz QPO is hard, which if confirmed would challenge the simple Comptonization model presented here.
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  • 25
    Publication Date: 2016-07-15
    Description: We describe a statistical approach for measuring the influence that a galaxy's closest companion has on the galaxy's properties out to arbitrarily wide separations. We begin by identifying the closest companion for every galaxy in a large spectroscopic sample of Sloan Digital Sky Survey galaxies. We then characterize the local environment of each galaxy by using the number of galaxies within 2 Mpc and by determining the isolation of the galaxy pair from other neighbouring galaxies. We introduce a sophisticated algorithm for creating a statistical control sample for each galaxy, matching on stellar mass, redshift, local density and isolation. Unlike traditional studies of close galaxy pairs, this approach is effective in a wide range of environments, regardless of how faraway the closest companion is (although a very distant closest companion is unlikely to have a measurable influence on the galaxy in question). We apply this methodology to measurements of galaxy asymmetry, and find that the presence of nearby companions drives a clear enhancement in galaxy asymmetries. The asymmetry excess peaks at the smallest projected separations (〈10 kpc), where the mean asymmetry is enhanced by a factor of 2.0 ± 0.2. Enhancements in mean asymmetry decline as pair separation increases, but remain statistically significant (1–2) out to projected separations of at least 50 kpc.
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  • 26
    Publication Date: 2016-07-15
    Description: The collimation of a Poynting-flux dominated jet by a wind emanating from the surface of an accretion flow is computed using a semi-analytic model. The injection of the disc wind is treated as a boundary condition in the equatorial plane, and its evolution is followed by invoking a prescribed geometry of streamlines. Solutions are obtained for a wide range of disc wind parameters. It is found that jet collimation generally occurs when the total wind power exceeds about 10 percents of the jet power. For moderate wind powers, we find gradual collimation. For strong winds, we find rapid collimation followed by focusing of the jet, after which it remains narrow over many Alfvén crossing times before becoming conical. We estimate that in the later case, the jet's magnetic field may be dissipated by the current-driven kink instability over a distance of a few hundreds gravitational radii. We apply the model to M87 and show that the observed parabolic shape of the radio jet within the Bondi radius can be reproduced provided that the wind injection zone extends to several hundreds gravitational radii, and that its total power is about one-third of the jet power. The radio spectrum can be produced by synchrotron radiation of relativistically hot, thermal electrons in the sheath flow surrounding the inner jet.
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  • 27
    Publication Date: 2016-07-15
    Description: We use ~100 cosmological galaxy formation ‘zoom-in’ simulations using the smoothed particle hydrodynamics code gasoline to study the effect of baryonic processes on the mass profiles of cold dark matter haloes. The haloes in our study range from dwarf ( M 200  ~ 10 10 M ) to Milky Way ( M 200  ~ 10 12 M ) masses. Our simulations exhibit a wide range of halo responses, primarily varying with mass, from expansion to contraction, with up to factor ~10 changes in the enclosed dark matter mass at 1 per cent of the virial radius. Confirming previous studies, the halo response is correlated with the integrated efficiency of star formation: SF ( M star / M 200 )/( b / m ). In addition, we report a new correlation with the compactness of the stellar system: R r 1/2 / R 200 . We provide an analytic formula depending on SF and R for the response of cold dark matter haloes to baryonic processes. An observationally testable prediction is that, at fixed mass, larger galaxies experience more halo expansion, while the smaller galaxies more halo contraction. This diversity of dark halo response is captured by a toy model consisting of cycles of adiabatic inflow (causing contraction) and impulsive gas outflow (causing expansion). For net outflow, or equal inflow and outflow fractions, f , the overall effect is expansion, with more expansion with larger f . For net inflow, contraction occurs for small f (large radii), while expansion occurs for large f (small radii), recovering the phenomenology seen in our simulations. These regularities in the galaxy formation process provide a step towards a fully predictive model for the structure of cold dark matter haloes.
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  • 28
    Publication Date: 2016-07-15
    Description: The strongest transitions of Zn and Cr ii are the most sensitive to relative variations in the fine-structure constant (α/α) among the transitions commonly observed in quasar absorption spectra. They also lie within just 40 Å of each other (rest frame), so they are resistant to the main systematic error affecting most previous measurements of α/α: long-range distortions of the wavelength calibration. While Zn and Cr ii absorption is normally very weak in quasar spectra, we obtained high signal-to-noise, high-resolution echelle spectra from the Keck and Very Large Telescopes of nine rare systems where it is strong enough to constrain α/α from these species alone. These provide 12 independent measurements (three quasars were observed with both telescopes) at redshifts 1.0–2.4, 11 of which pass stringent reliability criteria. These 11 are all consistent with α/α = 0 within their individual uncertainties of 3.5–13 parts per million (ppm), with a weighted mean α/α = 0.4 ± 1.4 stat ± 0.9 sys  ppm (1 statistical and systematic uncertainties), indicating no significant cosmological variations in α. This is the first statistical sample of absorbers that is resistant to long-range calibration distortions (at the 〈1 ppm level), with a precision comparable to previous large samples of ~150 (distortion-affected) absorbers. Our systematic error budget is instead dominated by much shorter range distortions repeated across echelle orders of individual spectra.
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  • 29
    Publication Date: 2016-07-15
    Description: We use the eagle suite of cosmological hydrodynamical simulations to study how the H i content of present-day galaxies depends on their environment. We show that eagle reproduces observed H i mass–environment trends very well, while semi-analytic models typically overpredict the average H i masses in dense environments. The environmental processes act primarily as an on/off switch for the H i content of satellites with M * 〉 10 9 M . At a fixed M * , the fraction of H i -depleted satellites increase with increasing host halo mass M 200 in response to stronger environmental effects, while at a fixed M 200 it decreases with increasing satellite M * as the gas is confined by deeper gravitational potentials. H i -depleted satellites reside mostly, but not exclusively, within the virial radius r 200 of their host halo. We investigate the origin of these trends by focusing on three environmental mechanisms: ram pressure stripping by the intragroup medium, tidal stripping by the host halo and satellite–satellite encounters. By tracking back in time the evolution of the H i -depleted satellites, we find that the most common cause of H i removal is satellite encounters. The time-scale for H i removal is typically less than 0.5 Gyr. Tidal stripping occurs in haloes of M 200 〈 10 14 M within 0.5 x r 200 , while the other processes act also in more massive haloes, generally within r 200 . Conversely, we find that ram pressure stripping is the most common mechanism that disturbs the H i morphology of galaxies at redshift z = 0. This implies that H i removal due to satellite–satellite interactions occurs on shorter time-scales than the other processes.
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  • 30
    Publication Date: 2016-07-15
    Description: We present the first numerical simulations in coupled dark energy cosmologies with high enough resolution to investigate the effects of the coupling on galactic and subgalactic scales. We choose two constant couplings and a time-varying coupling function and we run simulations of three Milky Way-sized haloes (~10 12  M ), a lower mass halo (6 x 10 11  M ) and a dwarf galaxy halo (5 x 10 9  M ). We resolve each halo with several million dark matter particles. On all scales, the coupling causes lower halo concentrations and a reduced number of substructures with respect to cold dark matter (CDM). We show that the reduced concentrations are not due to different formation times. We ascribe them to the extra terms that appear in the equations describing the gravitational dynamics. On the scale of the Milky Way satellites, we show that the lower concentrations can help in reconciling observed and simulated rotation curves, but the coupling values necessary to have a significant difference from CDM are outside the current observational constraints. On the other hand, if other modifications to the standard model allowing a higher coupling (e.g. massive neutrinos) are considered, coupled dark energy can become an interesting scenario to alleviate the small-scale issues of the CDM model.
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  • 31
    Publication Date: 2016-07-15
    Description: The correlation between radio spectral index and redshift has been exploited to discover high-redshift radio galaxies, but its underlying cause is unclear. It is crucial to characterize the particle acceleration and loss mechanisms in high-redshift radio galaxies to understand why their radio spectral indices are steeper than their local counterparts. Low-frequency information on scales of ~1 arcsec are necessary to determine the internal spectral index variation. In this paper we present the first spatially resolved studies at frequencies below 100 MHz of the z = 2.4 radio galaxy 4C 43.15 which was selected based on its ultrasteep spectral index (α 〈 –1; S ~ α ) between 365 MHz and 1.4 GHz. Using the International Low Frequency Array Low Band Antenna we achieve subarcsecond imaging resolution at 55 MHz with very long baseline interferometry techniques. Our study reveals low-frequency radio emission extended along the jet axis, which connects the two lobes. The integrated spectral index for frequencies 〈500 MHz is –0.83. The lobes have integrated spectral indices of –1.31 ± 0.03 and –1.75 ± 0.01 for frequencies ≥1.4 GHz, implying a break frequency between 500 MHz and 1.4 GHz. These spectral properties are similar to those of local radio galaxies. We conclude that the initially measured ultrasteep spectral index is due to a combination of the steepening spectrum at high frequencies with a break at intermediate frequencies.
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  • 32
    Publication Date: 2016-07-15
    Description: We examine a sample of 1495 galaxies in the CANDELS fields to determine the evolution of two-component galaxies, including bulges and discs, within massive galaxies at the epoch 1 〈  z  〈 3 when the Hubble sequence forms. We fit all of our galaxies’ light profiles with a single Sérsic fit, as well as with a combination of exponential and Sérsic profiles. The latter is done in order to describe a galaxy with an inner and an outer component, or bulge and disc component. We develop and use three classification methods (visual, F -test and the residual flux fraction) to separate our sample into one-component galaxies (disc/spheroids-like galaxies) and two-component galaxies (galaxies formed by an ‘inner part’ or bulge and an ‘outer part’ or disc). We then compare the results from using these three different ways to classify our galaxies. We find that the fraction of galaxies selected as two-component galaxies increases on average 50 per cent from the lowest mass bin to the most massive galaxies, and decreases with redshift by a factor of 4 from z  = 1 to 3. We find that single Sérsic ‘disc-like’ galaxies have the highest relative number densities at all redshifts, and that two-component galaxies have the greatest increase and become at par with Sérsic discs by z  = 1. We also find that the systems we classify as two-component galaxies have an increase in the sizes of their outer components, or ‘discs’, by about a factor of 3 from z  = 3 to 1.5, while the inner components or ‘bulges’ stay roughly the same size. This suggests that these systems are growing from the inside out, whilst the bulges or protobulges are in place early in the history of these galaxies. This is also seen to a lesser degree in the growth of single ‘disc-like’ galaxies versus ‘spheroid-like’ galaxies over the same epoch.
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  • 33
    Publication Date: 2016-07-15
    Description: Using the idea of regularization of singularities due to the variability of the fundamental constants in cosmology we study the cyclic universe models. We find two models of oscillating and non-singular mass density and pressure (‘non-singular’ bounce) regularized by varying gravitational constant G despite the scale factor evolution is oscillating and having sharp turning points (‘singular’ bounce). Both violating (big-bang) and non-violating (phantom) null energy condition models appear. Then, we extend this idea on to the multiverse containing cyclic individual universes with either growing or decreasing entropy though leaving the net entropy constant. In order to get an insight into the key idea, we consider the doubleverse with the same geometrical evolution of the two ‘parallel’ universes with their physical evolution [physical coupling constants c ( t ) and G ( t )] being different. An interesting point is that there is a possibility to exchange the universes at the point of maximum expansion – the fact which was already noticed in quantum cosmology. Similar scenario is also possible within the framework of Brans–Dicke theory where varying G ( t ) is replaced by the dynamical Brans–Dicke field ( t ) though these theories are slightly different.
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  • 34
    Publication Date: 2016-07-15
    Description: In the thermal dark matter (DM) paradigm, primordial interactions between DM and Standard Model particles are responsible for the observed DM relic density. In Bœhm et al., we showed that weak-strength interactions between DM and radiation (photons or neutrinos) can erase small-scale density fluctuations, leading to a suppression of the matter power spectrum compared to the collisionless cold DM (CDM) model. This results in fewer DM subhaloes within Milky Way-like DM haloes, implying a reduction in the abundance of satellite galaxies. Here we use very high-resolution N -body simulations to measure the dynamics of these subhaloes. We find that when interactions are included, the largest subhaloes are less concentrated than their counterparts in the collisionless CDM model and have rotation curves that match observational data, providing a new solution to the ‘too big to fail’ problem.
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  • 35
    Publication Date: 2016-07-15
    Description: The recent discovery of the gravitational wave source GW150914 has revealed a coalescing binary black hole (BBH) with masses of ~30 M . Previous proposals for the origin of such a massive binary include Population III (PopIII) stars. PopIII stars are efficient producers of BBHs and of a gravitational wave background (GWB) in the 10–100 Hz band, and also of ionizing radiation in the early Universe. We quantify the relation between the amplitude of the GWB ( gw ) and the electron scattering optical depth ( e ), produced by PopIII stars, assuming that f esc 10 per cent of their ionizing radiation escapes into the intergalactic medium. We find that PopIII stars would produce a GWB that is detectable by the future O5 LIGO/Virgo if e 0.07, consistent with the recent Planck measurement of e = 0.055 ± 0.09. Moreover, the spectral index of the background from PopIII BBHs becomes as small as dln gw /dln f 0.3 at f 30 Hz, which is significantly flatter than the value ~2/3 generically produced by lower redshift and less-massive BBHs. A detection of the unique flattening at such low frequencies by the O5 LIGO/Virgo will indicate the existence of a high-chirp mass, high-redshift BBH population, which is consistent with the PopIII origin. A precise characterization of the spectral shape near 30–50 Hz by the Einstein Telescope could also constrain the PopIII initial mass function and star formation rate.
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  • 36
    Publication Date: 2016-07-15
    Description: We employ very high resolution simulations of isolated Milky Way-like galaxies to study the effect of triaxial dark matter haloes on exponential stellar discs. Non-adiabatic halo shape changes can trigger two-armed grand-design spiral structures which extend all the way to the edge of the disc. Their pattern speed coincides with the inner Lindblad resonance indicating that they are kinematic density waves which can persist up to several Gyr. In dynamically cold discs, grand-design spirals are swing amplified and after a few Gyr can lead to the formation of (multi-armed) transient recurrent spirals. Stellar discs misaligned to the principal planes of the host triaxial halo develop characteristic integral shaped warps, but otherwise exhibit very similar spiral structures as aligned discs. For the grand-design spirals in our simulations, their strength dependence with radius is determined by the torque on the disc, suggesting that by studying grand-design spirals without bars it may be possible to set constraints on the tidal field and host dark matter halo shape.
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  • 37
    Publication Date: 2016-07-15
    Description: Intrinsic galaxy shape and angular momentum alignments can arise in cosmological large-scale structure due to tidal interactions or galaxy formation processes. Cosmological hydrodynamical simulations have recently come of age as a tool to study these alignments and their contamination to weak gravitational lensing. We probe the redshift and luminosity evolution of intrinsic alignments in Horizon-AGN between z = 0 and 3 for galaxies with an r -band absolute magnitude of M r ≤ –20. Alignments transition from being radial at low redshifts and high luminosities, dominated by the contribution of ellipticals, to being tangential at high redshift and low luminosities, where discs dominate the signal. This cannot be explained by the evolution of the fraction of ellipticals and discs alone: intrinsic evolution in the amplitude of alignments is necessary. The alignment amplitude of elliptical galaxies alone is smaller in amplitude by a factor of ~=2, but has similar luminosity and redshift evolution as in current observations and in the non-linear tidal alignment model at projected separations of 1 Mpc. Alignments of discs are null in projection and consistent with current low-redshift observations. The combination of the two populations yields an overall amplitude a factor of ~=4 lower than observed alignments of luminous red galaxies with a steeper luminosity dependence. The restriction on accurate galaxy shapes implies that the galaxy population in the simulation is complete only to M r ≤ –20. Higher resolution simulations will be necessary to avoid extrapolation of the intrinsic alignment predictions to the range of luminosities probed by future surveys.
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  • 38
    Publication Date: 2016-07-15
    Description: The spins of stellar-mass black holes (BHs) and the power outputs of their jets are measurable quantities. Unfortunately, the currently employed methods do not agree and the results are controversial. Two major issues concern the measurements of BH spin and beam (jet) power. The former issue can be resolved by future observations. But the latter issue can be resolved now, if we pay attention to what is expected from theoretical considerations. The question of whether a correlation has been found between the power outputs of few objects and the spins of their BHs is moot because BH beam power does not scale with the square of the spin of the BH. We show that the theoretical BH beam power is a strongly non-linear function of spin that cannot be approximated by a quadratic relation, as is generally stated when the influence of the magnetic field is not accounted for in the Blandford & Znajek model. The BH beam power of ballistic jets should scale a lot more steeply with BH spin irrespective of the magnetic field assumed to thread the horizon and the spin range considered. This behaviour may already be visible in the analyses of radio observations by Narayan & McClintock and Russell et al. In agreement with previous studies, we also find that the power output that originates in the inner regions of the surrounding accretion discs is higher than that from the BHs and it cannot be ignored in investigations of continuous compact jets from these systems.
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  • 39
    Publication Date: 2016-07-15
    Description: We present deep spectroscopy of three Galactic planetary nebulae (PNe) with large abundance discrepancy factors: NGC 6153, M 1-42 and Hf 2-2. The spectra were obtained with Very Large Telescope/Ultraviolet and Visual Echelle Spectrograph and cover the whole optical range (3040–11 000 Å) with a spectral resolution of ~20 000. For all three PNe, several hundred emission lines were detected and identified, with more than 70 per cent of them as permitted lines. Most of these permitted lines are excited by recombination. Numerous weak optical recombination lines (ORLs) of O ii , C ii , N ii and Ne ii were detected in the spectra and accurate fluxes measured. Line flux tables were compiled and ready for use by the community of nebular astrophysics. These ORLs were critically analysed using the effective recombination coefficients recently calculated for the optical recombination spectrum of N ii and O ii under the physical conditions of photoionized gaseous nebulae. Plasma diagnostics based on the heavy element ORLs were carried out using the new atomic data. Elemental abundances derived from the ORLs were systematically higher than those derived from the collisionally excited lines (CELs) by a factor of ~11, 22 and 80 for NGC 6153, M 1-42 and Hf 2-2, respectively. The electron temperatures derived from the heavy element ORLs are systematically lower than those derived from the CELs. These ORL versus CEL abundance and temperature discrepancies, previously observed in the three PNe through deep spectroscopy with medium to low spectral resolution, are thus confirmed by our analysis of the deep echelle spectra using the new atomic data.
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  • 40
    Publication Date: 2016-07-15
    Description: The birth of the first luminous sources and the ensuing epoch of reionization are best studied via the redshifted 21-cm emission line, the signature of the first two imprinting the last. In this work, we present a fully Bayesian method, hibayes , for extracting the faint, global (sky-averaged) 21-cm signal from the much brighter foreground emission. We show that a simplified (but plausible) Gaussian model of the 21-cm emission from the Cosmic Dawn epoch (15 z 30), parametrized by an amplitude $A_{\rm H\,\small {I}}$ , a frequency peak $\nu _{\rm H\,\small {I}}$ and a width $\sigma _{\rm H\,\small {I}}$ , can be extracted even in the presence of a structured foreground frequency spectrum (parametrized as a seventh-order polynomial), provided sufficient signal-to-noise (400 h of observation with a single dipole). We apply our method to an early, 19-min-long observation from the Large aperture Experiment to detect the Dark Ages, constraining the 21-cm signal amplitude and width to be $-890 \lt A_{\rm H\,\small {I}} \lt 0$ mK and $\sigma _{\rm H\,\small {I}} \gt 6.5$ MHz (corresponding to z 〉 1.9 at redshift z ~= 20) respectively at the 95-per cent confidence level in the range 13.2 〈 z 〈 27.4 (100 〉 〉 50 MHz).
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  • 41
    Publication Date: 2016-07-15
    Description: Several dedicated surveys focusing on early-type galaxies (ETGs) reveal that significant fractions of them are detectable in all interstellar medium phases studied to date. We select ETGs from the Herschel Reference Survey that have both far-infrared Herschel and either H  i or CO detection (or both). We derive their star formation rates (SFRs), stellar masses and dust masses via modelling their spectral energy distributions. We combine these with literature information on their atomic and molecular gas properties, in order to relate their star formation, total gas mass and dust mass on global scales. The ETGs deviate from the dust mass–SFR relation and the Schmidt–Kennicutt relation that SDSS star-forming galaxies define: compared to SDSS galaxies, ETGs have more dust at the same SFR, or less SFR at the same dust mass. When placing them in the M * –SFR plane, ETGs show a much lower specific SFR as compared to normal star-forming galaxies. ETGs show a large scatter compared to the Schmidt–Kennicutt relation found locally within our Galaxy, extending to lower SFRs and gas mass surface densities. Using an ETG's SFR and the Schmidt–Kennicutt law to predict its gas mass leads to an underestimate. ETGs have similar observed-gas-to-modelled-dust mass ratios to star-forming galaxies of the same stellar mass, as well as they exhibit a similar scatter.
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  • 42
    Publication Date: 2016-07-15
    Description: We report on the identification of the new Galactic Centre (GC) transient Swift J174540.7–290015 as a likely low-mass X-ray binary located at only 16 arcsec from Sgr A * . This transient was detected on 2016 February 6, during the Swift GC monitoring, and it showed long-term spectral variations compatible with a hard- to soft-state transition. We observed the field with XMM–Newton on February 26 for 35 ks, detecting the source in the soft state, characterized by a low level of variability and a soft X-ray thermal spectrum with a high energy tail (detected by INTEGRAL up to ~50 keV), typical of either accreting neutron stars or black holes. We observed: (i) a high column density of neutral absorbing material, suggesting that Swift J174540.7–290015 is located near or beyond the GC and; (ii) a sub-Solar iron abundance, therefore we argue that iron is depleted into dust grains. The lack of detection of Fe K absorption lines, eclipses or dipping suggests that the accretion disc is observed at a low inclination angle. Radio (Very Large Array) observations did not detect any radio counterpart to Swift J174540.7–290015. No evidence for X-ray or radio periodicity is found. The location of the transient was observed also in the near-infrared (near-IR) with gamma-ray burst optical near-IR detector at MPG/European Southern Observatory La Silla 2.2 m telescope and VLT/ NaCo pre- and post-outburst. Within the Chandra error region, we find multiple objects that display no significant variations.
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  • 43
    Publication Date: 2016-07-15
    Description: This is the first of two papers describing the observations and cataloguing of deep 3-GHz observations of the Lockman Hole North using the Karl G. Jansky Very Large Array. The aim of this paper is to investigate, through the use of simulated images, the uncertainties and accuracy of source-finding routines, as well as to quantify systematic effects due to resolution, such as source confusion and source size. While these effects are not new, this work is intended as a particular case study that can be scaled and translated to other surveys. We use the simulations to derive uncertainties in the fitted parameters, as well as bias corrections for the actual catalogue (presented in Paper II). We compare two different source-finding routines, OBIT and AEGEAN, and two different effective resolutions, 8 and 2.75  arcsec. We find that the two routines perform comparably well, with OBIT being slightly better at de-blending sources, but slightly worse at fitting resolved sources. We show that 30–70 per cent of sources are missed or fit inaccurately once the source size becomes larger than the beam, possibly explaining source count errors in high-resolution surveys. We also investigate the effect of blending, finding that any sources with separations smaller than the beam size are fit as single sources. We show that the use of machine-learning techniques can correctly identify blended sources up to 90 per cent of the time, and prior-driven fitting can lead to a 70 per cent improvement in the number of de-blended sources.
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  • 44
    Publication Date: 2016-07-15
    Description: We present evidence for a small glitch in the spin evolution of the millisecond pulsar J0613–0200, using the EPTA Data Release 1.0, combined with Jodrell Bank analogue filterbank times of arrival (TOAs) recorded with the Lovell telescope and Effelsberg Pulsar Observing System TOAs. A spin frequency step of 0.82(3) nHz and frequency derivative step of –1.6(39)  x  10 –19 Hz s –1 are measured at the epoch of MJD 50888(30). After PSR B1821–24A, this is only the second glitch ever observed in a millisecond pulsar, with a fractional size in frequency of / = 2.5(1)  x  10 –12 , which is several times smaller than the previous smallest glitch. PSR J0613–0200 is used in gravitational wave searches with pulsar timing arrays, and is to date only the second such pulsar to have experienced a glitch in a combined 886 pulsar-years of observations. We find that accurately modelling the glitch does not impact the timing precision for pulsar timing array applications. We estimate that for the current set of millisecond pulsars included in the International Pulsar Timing Array, there is a probability of ~50 per cent that another glitch will be observed in a timing array pulsar within 10 years.
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  • 45
    Publication Date: 2016-07-15
    Description: We exploit Atacama Large Interferometer Array (ALMA) 870 μm observations to measure the star formation rates (SFRs) of eight X-ray detected active galactic nuclei (AGNs) in a z 3.1 protocluster, four of which reside in extended Lyα haloes (often termed Lyman-alpha blobs: LABs). Three of the AGNs are detected by ALMA and have implied SFRs of 220–410 M  yr –1 ; the non-detection of the other five AGNs places SFR upper limits of 210 M  yr –1 . The mean SFR of the protocluster AGNs (110–210 M  yr –1 ) is consistent (within a factor of 0.7–2.3) with that found for co-eval AGNs in the field, implying that the galaxy growth is not significantly accelerated in these systems. However, when also considering ALMA data from the literature, we find evidence for elevated mean SFRs (up-to a factor of 5.9 over the field) for AGNs at the protocluster core, indicating that galaxy growth is significantly accelerated in the central regions of the protocluster. We also show that all of the four protocluster LABs are associated with an ALMA counterpart within the extent of their Lyα emission. The SFRs of the ALMA sources within the LABs (150–410 M  yr –1 ) are consistent with those expected for co-eval massive star-forming galaxies in the field. Furthermore, the two giant LABs (with physical extents of 100 kpc) do not host more luminous star formation than the smaller LABs, despite being an order of magnitude brighter in Lyα emission. We use these results to discuss star formation as the power source of LABs.
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  • 46
    Publication Date: 2016-07-15
    Description: We present the discovery of a new, peculiar form of double-periodic pulsation in RR Lyrae stars. In four, long-period ( P 〉 0.6 d) stars observed by the Optical Gravitational Lensing Experiment, and classified as fundamental mode pulsators (RRab), we detect additional, low-amplitude variability, with period shorter than fundamental mode period. The period ratios fall in a range similar to double-mode fundamental and first overtone RR Lyrae stars (RRd), with the exception of one star, in which the period ratio is significantly lower and nearly exactly equals 0.7. Although period ratios are fairly different for the four stars, the light-curve shapes corresponding to the dominant, fundamental mode are very similar. The peak-to-peak amplitudes and amplitude ratios (Fourier parameters R 21 and R 31 ) are among the highest observed in RRab stars of similar period, while Fourier phases ( 21 and 31 ) are among the lowest observed in RRab stars. If the additional variability is interpreted as due to radial first overtone, then, the four stars are the most extreme RRd variables of the longest pulsation periods known. Indeed, the observed period ratios can be well modelled with high-metallicity pulsation models. However, at such long pulsation periods, first overtone is typically damped. Five other candidates, with weak signature of additional variability, sharing the same characteristics, were also detected and are briefly discussed.
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  • 47
    Publication Date: 2016-07-15
    Description: The Laser Interferometer Gravitational-Wave Observatory (LIGO) detection of gravitational waves that take away 5 per cent of the total mass of two merging black holes points out on the importance of considering varying gravitational mass of a system in the framework of the Einstein general theory of relativity. We calculate the acceleration of a particle in the non-stationary field of a quasi-spherical system composed of a large number of objects emitting gravitational waves. It is shown that reduction of the gravitational mass of the system due to emitting gravitational waves leads to a repulsive gravitational force that diminishes with time but never disappears. This repulsive force may be related to the observed expansion of the Universe.
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  • 48
    Publication Date: 2016-07-15
    Description: Radiative feedback is an important consequence of cluster formation in giant molecular clouds (GMCs) in which newly formed clusters heat and ionize their surrounding gas. The process of cluster formation, and the role of radiative feedback, has not been fully explored in different GMC environments. We present a suite of simulations which explore how the initial gravitational boundedness, and radiative feedback, affect cluster formation. We model the early evolution (〈5 Myr) of turbulent, 10 6 M clouds with virial parameters ranging from 0.5 to 5. To model cluster formation, we use cluster sink particles, coupled to a raytracing scheme, and a custom subgrid model which populates a cluster via sampling an initial mass function (IMF) with an efficiency of 20 per cent per free-fall time. We find that radiative feedback only decreases the cluster particle formation efficiency by a few per cent. The initial virial parameter plays a much stronger role in limiting cluster formation, with a spread of cluster formation efficiencies of 37–71 per cent for the most unbound to the most bound model. The total number of clusters increases while the maximum mass cluster decreases with an increasing initial virial parameter, resulting in steeper mass distributions. The star formation rates in our cluster particles are initially consistent with observations but rise to higher values at late times. This suggests that radiative feedback alone is not responsible for dispersing a GMC over the first 5 Myr of cluster formation.
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  • 49
    Publication Date: 2016-07-15
    Description: Large redshift surveys capable of measuring the baryon acoustic oscillation (BAO) signal have proven to be an effective way of measuring the distance–redshift relation in cosmology. Building off the work in Zhu et al., we develop a technique to directly constrain the distance–redshift relation from BAO measurements without splitting the sample into redshift bins. We apply the redshift weighting technique in Zhu et al. to the clustering of galaxies from 1000 Quick particle mesh (QPM) mock simulations after reconstruction and achieve a 0.75 per cent measurement of the angular diameter distance D A at z = 0.64 and the same precision for Hubble parameter H at z = 0.29. These QPM mock catalogues mimic the clustering and noise level of the Baryon Oscillation Spectroscopic Survey Data Release 12 (DR12). We compress the correlation functions in the redshift direction on to a set of weighted correlation functions. These estimators give unbiased D A and H measurements across the entire redshift range of the combined sample. We demonstrate the effectiveness of redshift weighting in improving the distance and Hubble parameter estimates. Instead of measuring at a single ‘effective’ redshift as in traditional analyses, we report our D A and H measurements at all redshifts. The measured fractional error of D A ranges from 1.53 per cent at z = 0.2 to 0.75 per cent at z = 0.64. The fractional error of H ranges from 0.75 per cent at z = 0.29 to 2.45 per cent at z = 0.7. Our measurements are consistent with a Fisher forecast to within 10–20 per cent depending on the pivot redshift. We further show the results are robust against the choice of fiducial cosmologies, galaxy bias models, and redshift–space distortions streaming parameters.
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  • 50
    Publication Date: 2016-07-15
    Description: The dwarf spheroidal galaxies (dSphs) in the Milky Way are the primary targets in the indirect searches for particle dark matter. To set robust constraints on candidate dark matter particles, understanding the dark halo structure of these systems is of substantial importance. In this paper, we first evaluate the astrophysical factors for dark matter annihilation and decay for 24 dSphs, taking into account a non-spherical dark halo, using generalized axisymmetric mass models based on axisymmetric Jeans equations. First, from a fitting analysis of the most recent kinematic data available, our axisymmetric mass models are a much better fit than previous spherical ones, thus, our work should be the most realistic and reliable estimator for astrophysical factors. Secondly, we find that among analysed dSphs, the ultra-faint dwarf galaxies Triangulum II and Ursa Major II are the most promising but large uncertain targets for dark matter annihilation while the classical dSph Draco is the most robust and detectable target for dark matter decay. It is also found that the non-sphericity of luminous and dark components influences the estimate of astrophysical factors, even though these factors largely depend on the sample size, the prior range of parameters and the spatial extent of the dark halo. Moreover, owing to these effects, the constraints on the dark matter annihilation cross-section are more conservative than those of previous spherical works. These results are important for optimizing and designing dark matter searches in current and future multi-messenger observations by space and ground-based telescopes.
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  • 51
    Publication Date: 2016-07-15
    Description: We investigate how nightside cooling and surface friction affect surface temperatures and large-scale circulation for tidally locked Earth-like planets. For each scenario, we vary the orbital period between P rot = 1 and 100 d and capture changes in climate states. We find drastic changes in climate states for different surface friction scenarios. For very efficient surface friction ( t s,fric = 0.1 d), the simulations for short rotation periods ( P rot ≤ 10 d) show predominantly standing extratropical Rossby waves. These waves lead to climate states with two high-latitude westerly jets and unperturbed meridional direct circulation. In most other scenarios, simulations with short rotation periods exhibit instead dominance by standing tropical Rossby waves. Such climate states have a single equatorial westerly jet, which disrupts direct circulation. Experiments with weak surface friction ( t s,fric = 10–100 d) show decoupling between surface temperatures and circulation, which leads to strong cooling of the nightside. The experiment with t s,fric = 100 d assumes climate states with easterly flow (retrograde rotation) for medium and slow planetary rotations P rot = 12–100 d. We show that an increase of nightside cooling efficiency by one order of magnitude compared to the nominal model leads to a cooling of the nightside surface temperatures by 80–100 K. The dayside surface temperatures only drop by 25 K at the same time. The increase in thermal forcing suppresses the formation of extratropical Rossby waves on small planets ( R P = 1 R Earth ) in the short rotation period regime ( P rot ≤ 10 d).
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  • 52
    Publication Date: 2016-07-15
    Description: Using detailed modelling, we analyse the spectra observed from the sample galaxies at z  ~ 0.8 presented by Ly et al., constraining the models by the [O iii ]5007+4959/[O iii ]4363 line ratios. Composite models (shock + photoionization) are adopted. Shock velocities ≥100 km s –1 and pre-shock densities n 0  ~ 200 cm –3 characterize the gas surrounding the starburst (SB), while n 0 are higher by a factor of 1.5–10 in the AGN emitting gas. SB effective temperatures are similar to those of quiescent galaxies ( T * ~ 4–7  x  10 4  K). Cloud geometrical thicknesses in the SB are ≤10 16  cm, indicating major fragmentation, while in AGN they reach 〉10 pc. O/H are about solar for all the objects, except for a few AGN clouds with O/H = 0.3–0.5 solar. SB models reproduce most of the data within the observational errors. About half of the objects’ spectra are well fitted by an accreting AGN. Some galaxies show multiple radiation sources, such as SB + AGN, or a double AGN.
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  • 53
    Publication Date: 2016-07-15
    Description: We present a method of comparing the Galactic systems realized by two astrometric catalogues. The systematic differences between positions and proper motions are represented by vector spherical harmonics. To extract the signal from the noise, we use a statistical criterion adapted to using healpix data pixelization to determine the significance of all the accessible harmonics. We also use a new analytical method that includes the magnitude equation in the vector spherical harmonics technique. The influence of the magnitude equation on the determination of the mutual orientation and rotation of the PPMXL and UCAC4 Galactic reference frames has been found in the range of J magnitudes from 10.25 to 15.75 mag. The angles of mutual orientation and the rates of mutual rotation of the Galactic frames under consideration depend on magnitude and can reach the level of 10 mas in orientation and 0.7 mas yr –1 for spin. We make a kinematic study of the low degree harmonics in the representation of the systematic differences between the Galactic proper motions. We have found that, averaged over the magnitude range, the biases of the Oort constants due to systematic differences of proper motions between the two catalogues, which are as large as 〈 A 〉 = 1.60 ± 0.41 and 〈 B 〉 = –1.91 ± 0.32 km s –1 kpc –1 , are greater than the standard errors of their evaluation in the systems of these catalogues. The theoretical equations used in this paper are based on real vector harmonics. We present a set of formulae to convert them into the complex function formalism.
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  • 54
    Publication Date: 2016-07-15
    Description: We present a way of searching for non-transiting exoplanets with dusty tails. In the transiting case, the extinction by dust during the transit removes more light from the beam than is scattered into it. Thus, the forward scattering component of the light is best seen either just prior to ingress, or just after egress, but with reduced amplitude over the larger peak that is obscured by the transit. This picture suggests that it should be equally productive to search for positive-going peaks in the flux from non-transiting exoplanets with dusty tails. We discuss what amplitudes are expected for different orbital inclination angles. The signature of such objects should be distinct from normal transits, starspots, and most – but not all – types of stellar pulsations.
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  • 55
    Publication Date: 2016-07-15
    Description: We present results from three-dimensional, numerical relativity simulations of a tilted black hole-thick accretion disc system. The simulations are analysed using tracer particles in the disc which are advected with the flow. Such tracers, which we employ in these new simulations for the first time, provide a powerful means to analyse in detail the complex dynamics of tilted black hole–torus systems. We show how its use helps to gain insight into the overall dynamics of the system, discussing the origin of the observed black hole precession and the development of a global non-axisymmetric m = 1 mode in the disc. Our three-dimensional simulations show the presence of quasi-periodic oscillations (QPOs) in the instantaneous accretion rate, with frequencies in a range compatible with those observed in low-mass X-ray binaries with either a black hole or a neutron star component. The frequency ratio of the dominant low-frequency peak and the first overtone is o 1 / f ~ 1.9, a frequency ratio not attainable when modelling the QPOs as p -mode oscillations in axisymmetric tori.
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  • 56
    Publication Date: 2016-07-15
    Description: We present a multiwavelength investigation of the young stellar population and star formation activities around the H ii region Sharpless 311. Using our deep near-infrared observations and archival Spitzer -IRAC observations, we have detected a total of 125 young stellar objects (YSOs) in an area of ~86 arcmin 2 . The YSO sample includes eight Class I and 117 Class II candidate YSOs. The mass completeness of the identified YSO sample is estimated to be 1.0 M . The ages and masses of the majority of the candidate YSOs are estimated to be in the range ~0.1–5 Myr and ~0.3–6 M , respectively. The 8-μm image of S311 displays an approximately spherical cavity around the ionizing source, which was possibly created by the expansion of the H ii region. The spatial distribution of the candidate YSOs reveals that a significant number of them are distributed systematically along the 8-μm emission with a majority clustered around the eastern border of the H ii region. Four clumps/compact H ii regions are detected in the radio continuum observations at 1280 MHz, which may have been formed during the expansion of the H ii region. The estimated dynamical age of the region, main-sequence lifetime of the ionizing source, the spatial distribution and ages of the candidate YSOs indicate triggered star formation in the complex.
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  • 57
    Publication Date: 2016-07-17
    Description: NGC 6946, known as the Fireworks galaxy because of its high supernova rate and high star formation, is embedded in a very extended H i halo. Its northern spiral arm is well detached from the galactic main body. We found that this arm contains a large (~300 pc in size) Red Ellipse, named according to a strong contamination of the Hα emission line on its optical images. The ellipse is accompanied by a short parallel arc and a few others still smaller and less regular; a bright star cluster is seen inside these features. The complicated combination of arcs seems to be unique; it is only a bit similar to some SNRs. However, the long-slit spectral data obtained with the Russian 6-m telescope did not confirm the origin of the nebula as a result of a single SN outburst. The emission-line spectrum corresponds to the photoionization by young hot stars with a small contribution of shock ionization. The most likely explanation of the Red Ellipse is a superbubble created by a collective feedback of massive stars in the star cluster located in the NE side of the Red Ellipse. However, the very regular elliptical shape of the nebulae seems strange.
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  • 58
    Publication Date: 2016-07-17
    Description: Gravity is believed to be important on multiple physical scales in molecular clouds. However, quantitative constraints on gravity are still lacking. We derive an analytical formula which provides estimates on multiscale gravitational energy distribution using the observed surface density probability distribution function (PDF). Our analytical formalism also enables one to convert the observed column density PDF into an estimated volume density PDF, and to obtain average radial density profile ( r ). For a region with $N_{\rm col} \sim N^{-\gamma _{\rm N}}$ , the gravitational energy spectra is $E_{\rm p}(k)\sim k^{-4(1 - 1/\gamma _{\rm N})}$ . We apply the formula to observations of molecular clouds, and find that a scaling index of –2 of the surface density PDF implies that ~ r –2 and E p ( k ) ~ k –2 . The results are valid from the cloud scale (a few parsec) to around ~ 0.1 pc. Because of the resemblance the scaling index of the gravitational energy spectrum and the that of the kinetic energy power spectrum of the Burgers turbulence (where E ~ k –2 ), our result indicates that gravity can act effectively against turbulence over a multitude of physical scales. This is the critical scaling index which divides molecular clouds into two categories: clouds like Orion and Ophiuchus have shallower power laws, and the amount of gravitational energy is too large for turbulence to be effective inside the cloud. Because gravity dominates, we call this type of cloud g-type clouds. On the other hand, clouds like the California molecular cloud and the Pipe nebula have steeper power laws, and turbulence can overcome gravity if it can cascade effectively from the large scale. We call this type of cloud t-type clouds. The analytical formula can be used to determine if gravity is dominating cloud evolution when the column density PDF can be reliably determined.
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  • 59
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  • 61
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  • 62
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  • 63
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  • 64
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  • 65
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  • 66
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  • 67
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  • 68
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  • 69
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  • 70
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  • 71
    Publication Date: 2016-07-20
    Description: Ian Crawford , Martin Elvis and James Carpenter summarize an RAS Specialist Discussion Meeting which examined how science will benefit from the use of extraterrestrial resources.
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  • 72
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  • 73
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    Publication Date: 2016-07-20
    Description: Before they could join the RAS, many women were influential members of amateur astronomical societies across the country, as Allan Chapman explains.
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  • 74
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    Publication Date: 2016-07-20
    Description: Don Kurtz , Simon Jeffrey and Conny Aerts describe discoveries in the new era of precision asteroseismology.
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  • 75
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    Publication Date: 2016-07-20
    Description: A&G is branching out with an online platform where RAS Fellows can write about their activities, news and events, reports Sue Bowler .
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  • 76
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    Publication Date: 2016-07-20
    Description: COPERNICUS/ESA/PPO.LABS/NORUT/COMET-SEOM INSARAP STUDY In this issue's cover feature, Tim J Wright discusses the earthquake deformation cycle and seismic hazard in the continents – the 2015 Bullerwell Lecture.
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  • 77
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  • 78
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    Publication Date: 2016-07-20
    Description: The National Astronomy Meeting is in its 25th year. Ken Pounds looks back at how it started and how it has evolved.
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  • 79
    Publication Date: 2016-07-20
    Description: The next Galactic supernova is expected to bring great opportunities for the direct detection of gravitational waves (GW), full flavour neutrinos, and multiwavelength photons. To maximize the science return from such a rare event, it is essential to have established classes of possible situations and preparations for appropriate observations. To this end, we use a long-term numerical simulation of the core-collapse supernova (CCSN) of a 17 M red supergiant progenitor to self-consistently model the multimessenger signals expected in GW, neutrino, and electromagnetic messengers. This supernova model takes into account the formation and evolution of a protoneutron star, neutrino-matter interaction, and neutrino transport, all within a two-dimensional shock hydrodynamics simulation. With this, we separately discuss three situations: (i) a CCSN at the Galactic Center, (ii) an extremely nearby CCSN within hundreds of parsecs, and (iii) a CCSN in nearby galaxies within several Mpc. These distance regimes necessitate different strategies for synergistic observations. In a Galactic CCSN, neutrinos provide strategic timing and pointing information. We explore how these in turn deliver an improvement in the sensitivity of GW analyses and help to guarantee observations of early electromagnetic signals. To facilitate the detection of multimessenger signals of CCSNe in extremely nearby and extragalactic distances, we compile a list of nearby red supergiant candidates and a list of nearby galaxies with their expected CCSN rates. By exploring the sequential multimessenger signals of a nearby CCSN, we discuss preparations for maximizing successful studies of such an unprecedented stirring event.
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  • 80
    Publication Date: 2016-07-20
    Description: Recent observations of active galactic nucleus (AGN) activity in massive galaxies (log M * / M  〉 10.4) show the following: (1) at z 〈 1, AGN-hosting galaxies do not show enhanced merger signatures compared with normal galaxies, (2) also at z 〈 1, most AGNs are hosted by quiescent galaxies and (3) at z 〉 1, the percentage of AGNs in star-forming galaxies increases and becomes comparable to the AGN percentage in quiescent galaxies at z ~ 2. How can major mergers explain AGN activity in massive quiescent galaxies that have no merger features and no star formation to indicate a recent galaxy merger? By matching merger events in a cosmological N -body simulation to the observed AGN incidence probability in the COSMOS survey, we show that major merger-triggered AGN activity is consistent with the observations. By distinguishing between ‘peak’ AGNs (recently merger-triggered and hosted by star-forming galaxies) and ‘faded’ AGNs (merger-triggered a long time ago and now residing in quiescent galaxies), we show that the AGN occupation fraction in star-forming and quiescent galaxies simply follows the evolution of the galaxy merger rate. Since the galaxy merger rate drops dramatically at z 〈 1, the only AGNs left to be observed are the ones triggered by old mergers that are now in the declining phase of their nuclear activity, hosted by quiescent galaxies. As we go towards higher redshifts, the galaxy merger rate increases and the percentages of ‘peak’ AGNs and ‘faded’ AGNs become comparable.
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  • 81
    Publication Date: 2016-07-20
    Description: Relativistic jets can form from at least some tidal disruption events (TDEs) of (sub-)stellar objects around supermassive black holes. We detect the millimetre (MM) emission of IGR J12580+0134 – the nearest TDE known in the galaxy NGC 4845 at the distance of only 17 Mpc, based on Planck all-sky survey data. The data show significant flux jumps after the event, followed by substantial declines, in all six high-frequency Planck bands from 100 to 857 GHz. We further show that the evolution of the MM flux densities is well consistent with our model prediction from an off-axis jet, as was initially suggested from radio and X-ray observations. This detection represents the second TDE with MM detections; the other is Sw J1644+57, an on-axis jetted TDE at redshift of 0.35. Using the on- and off-axis jet models developed for these two TDEs as templates, we estimate the detection potential of similar events with the Large Millimeter Telescope (LMT) and the Atacama Large Millimeter/submillimeter Array (ALMA). Assuming an exposure of 1 h, we find that the LMT (ALMA) can detect jetted TDEs up to redshifts z ~ 1 (2), for a typical disrupted star mass of ~1 M . The detection rates of on- and off-axis TDEs can be as high as ~0.6 (13) and 10 (220) yr –1 , respectively, for the LMT (ALMA). We briefly discuss how such observations, together with follow-up radio monitoring, may lead to major advances in understanding the jetted TDEs themselves and the ambient environment of the circumnuclear medium.
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  • 82
    Publication Date: 2016-07-20
    Description: A debate has arisen concerning the fundamental nature of luminous blue variables (LBVs) and their role in stellar evolution. While Smith & Tombleson proposed that their isolated environments indicate that LBVs must be largely the product of binary evolution, Humphreys et al. have recently expressed the view that the traditional single-star view still holds if one appropriately selects a subsample of LBVs. This paper finds the claim of Humphreys et al. to be quantitatively unjustified. A statistical test of ‘candidate’ as opposed to ‘confirmed’ LBVs shows no significant difference (〈1) between their environments. Even if the sample is further subdivided as proposed, the three most luminous LBVs are spatially dispersed similar to late O-type dwarfs, which have much longer median lifetimes than expected for classical LBVs. The lower luminosity LBVs have a distribution associated with red supergiants (RSGs), but these RSGs are dominated by stars of 10–15 M initial mass, with much longer lifetimes than expected for those lower luminosity LBVs. If one's view is restricted to the highest luminosity LBVs, then the appropriate comparison is with early O-type stars that are their presumed progenitors; when this is done, it is clear that even the high-luminosity LBVs are more dispersed than expected. Humphreys et al. also suggest that velocities of LBVs support the single-star view, being inconsistent with runaways. A quantitative analysis of the radial velocity distribution of LBVS in M31 and M33 contradicts this; modest runway speeds expected from mass gainers in binary evolution are consistent with the observed velocities, although the data lack the precision to discriminate.
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  • 83
    Publication Date: 2016-07-20
    Description: Primordial dark matter (DM) haloes are the smallest gravitationally bound DM structures from which the first stars, black holes and galaxies form and grow in the early universe. However, their structures are sensitive to the free streaming scale of DM, which in turn depends on the nature of DM particles. In this work, we test the hypothesis that the slope of the central cusps in primordial DM haloes near the free streaming scale depends on the nature of merging process. By combining and analysing data from a cosmological simulation with the cutoff in the small-scale matter power spectrum as well as a suite of controlled, high-resolution simulations of binary mergers, we find that (1) the primordial DM haloes form preferentially through major mergers in radial orbits; (2) their central DM density profile is more susceptible to a merging process compared to that of galaxy- and cluster-sized DM haloes; (3) consecutive major mergers drive the central density slope to approach the universal form characterized by the Navarro–Frenk–White profile, which is shown to be robust to the impacts of mergers and serves an attractor solution for the density structure of DM haloes. Our work highlights the importance of dynamical processes on the structure formation during the Dark Ages.
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  • 84
    Publication Date: 2016-07-20
    Description: The discovery of lithium-rich giants contradicts expectations from canonical stellar evolution. Here we report on the serendipitous discovery of 20 Li-rich giants observed during the Gaia -ESO Survey, which includes the first nine Li-rich giant stars known towards the CoRoT fields. Most of our Li-rich giants have near-solar metallicities and stellar parameters consistent with being before the luminosity bump. This is difficult to reconcile with deep mixing models proposed to explain lithium enrichment, because these models can only operate at later evolutionary stages: at or past the luminosity bump. In an effort to shed light on the Li-rich phenomenon, we highlight recent evidence of the tidal destruction of close-in hot Jupiters at the sub-giant phase. We note that when coupled with models of planet accretion, the observed destruction of hot Jupiters actually predicts the existence of Li-rich giant stars, and suggests that Li-rich stars should be found early on the giant branch and occur more frequently with increasing metallicity. A comprehensive review of all known Li-rich giant stars reveals that this scenario is consistent with the data. However, more evolved or metal-poor stars are less likely to host close-in giant planets, implying that their Li-rich origin requires an alternative explanation, likely related to mixing scenarios rather than external phenomena.
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  • 85
    Publication Date: 2016-07-20
    Description: A key physical quantity during reionization is the size of H  ii regions. Previous studies found a characteristic bubble size which increases rapidly during reionization, with apparent agreement between simulations and analytic excursion set theory. Using four different methods, we critically examine this claim. In particular, we introduce the use of the watershed algorithm – widely used for void finding in galaxy surveys – which we show to be an unbiased method with the lowest dispersion and best performance on Monte Carlo realizations of a known bubble size probability density function (PDF). We find that a friends-of-friends algorithm declares most of the ionized volume to be occupied by a network of volume-filling regions connected by narrow tunnels. For methods tuned to detect the volume-filling regions, previous apparent agreement between simulations and theory is spurious, and due to a failure to correctly account for the window function of measurement schemes. The discrepancy is already obvious from visual inspection. Instead, H  ii regions in simulations are significantly larger (by factors of 10–1000 in volume) than analytic predictions. The size PDF is narrower, and evolves more slowly with time, than predicted. It becomes more sharply peaked as reionization progresses. These effects are likely caused by bubble mergers, which are inadequately modelled by analytic theory. Our results have important consequences for high-redshift 21 cm observations, the mean free path of ionizing photons, and the visibility of Lyα emitters, and point to a fundamental failure in our understanding of the characteristic scales of the reionization process.
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  • 86
    Publication Date: 2016-07-21
    Description: We present a model of cometary dust capable of simulating the dynamics within the first few tens of km of the comet surface. Recent measurements by the Grain Impact Analyser and Dust Accumulator and Cometary Secondary Ion Mass Analyser instruments on Rosetta show that the nucleus emits fluffy dust particles with porosities above 50 per cent and sizes up to at least mm (Fulle et al. 2015b ; Rotundi et al. 2015 ; Schulz et al. 2015 ). Retrieval of the physical properties of these particles requires a model of the effective forces governing their dynamics. Here, we present a model capable of simulating realistic, large and porous particles using hierarchical aggregates, which shows previous extrapolations to be inadequate. The main strengths of our approach are that we can simulate very large (mm-scale) non-spherical agglomerates and can accurately determine their (1) effective cross-section and ratio of cross-section to mass, (2) gas drag coefficient, and (3) light scattering properties. In practical terms, we find that a more detailed treatment of the dust structure results in three to five times higher velocities for large dust particles in the inner coma than previously estimated using spherical particles of the same mass. We apply our model to the dynamics of dust in the vicinity of the nucleus of comet 67P and successfully reproduce the dust speeds reported early on when the comet was roughly 3.5 au from the Sun. At this stage, we employ a simple spherical comet nucleus, we model activity as constant velocity gas expansion from a uniformly active surface, and use Mie scattering. We discuss pathways to improve on these simplifications in the future.
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  • 87
    Publication Date: 2016-07-21
    Description: This study represents the most sensitive Chandra X-ray point source catalogue of M31. Using 133 publicly available Chandra ACIS-I/S observations totalling ~1 Ms, we detected 795 X-ray sources in the bulge, north-east, and south-west fields of M31, covering an area of 0.6 deg 2 , to a limiting unabsorbed 0.5–8.0 keV luminosity of ~10 34 erg s –1 . In the inner bulge, where exposure is approximately constant, X-ray fluxes represent average values because they were determined from many observations over a long period of time. Similarly, our catalogue is more complete in the bulge fields since monitoring allowed more transient sources to be detected. The catalogue was cross-correlated with a previous XMM–Newton catalogue of M31's D 25 isophote consisting of 1948 X-ray sources, with only 979 within the field of view of our survey. We found 387 (49 per cent) of our Chandra sources (352 or 44 per cent unique sources) matched to within 5 arcsec of 352 XMM–Newton sources. Combining this result with matching done to previous Chandra X-ray sources we detected 259. new sources in our catalogue. We created X-ray luminosity functions (XLFs) in the soft (0.5–2.0 keV) and hard (2.0–8.0 keV) bands that are the most sensitive for any large galaxy based on our detection limits. Completeness-corrected XLFs show a break around 1.3 x 10 37 erg s –1 , consistent with previous work. As in past surveys, we find that the bulge XLFs are flatter than the disc, indicating a lack of bright high-mass X-ray binaries in the disc and an aging population of low-mass X-ray binaries in the bulge.
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  • 88
    Publication Date: 2016-07-21
    Description: We introduce a new transit search and vetting pipeline for observations from the K2 mission, and present the candidate transiting planets identified by this pipeline out of the targets in Campaigns 5 and 6. Our pipeline uses the Gaussian process-based k2sc code to correct for the K2 pointing systematics and simultaneously model stellar variability. The systematics-corrected, variability-detrended light curves are searched for transits with the box-least-squares method, and a period-dependent detection threshold is used to generate a preliminary candidate list. Two or three individuals vet each candidate manually to produce the final candidate list, using a set of automatically generated transit fits and assorted diagnostic tests to inform the vetting. We detect 145 single-planet system candidates and 5 multi-planet systems, independently recovering the previously published hot Jupiters EPIC 212110888b, WASP-55b (EPIC 212300977b) and Qatar-2b (EPIC 212756297b). We also report the outcome of reconnaissance spectroscopy carried out for all candidates with Kepler magnitude Kp ≤ 13, identifying 12 targets as likely false positives. We compare our results to those of other K2 transit search pipelines, noting that ours performs particularly well for variable and/or active stars, but that the results are very similar overall. All the light curves and code used in the transit search and vetting process are publicly available, as are the follow-up spectra.
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  • 89
    Publication Date: 2016-07-21
    Description: We use particle data from the Illustris simulation, combined with individual kinematic constraints on the mass of the Milky Way (MW) at specific distances from the Galactic Centre, to infer the radial distribution of the MW's dark matter halo mass. Our method allows us to convert any constraint on the mass of the MW within a fixed distance to a full circular velocity profile to the MW's virial radius. As primary examples, we take two recent (and discrepant) measurements of the total mass within 50 kpc of the Galaxy and find that they imply very different mass profiles and stellar masses for the Galaxy. The dark-matter-only version of the Illustris simulation enables us to compute the effects of galaxy formation on such constraints on a halo-by-halo basis; on small scales, galaxy formation enhances the density relative to dark-matter-only runs, while the total mass density is approximately 20 per cent lower at large Galactocentric distances. We are also able to quantify how current and future constraints on the mass of the MW within specific radii will be reflected in uncertainties on its virial mass: even a measurement of M (〈50 kpc) with essentially perfect precision still results in a 20 per cent uncertainty on the virial mass of the Galaxy, while a future measurement of M (〈100 kpc) with 10 per cent errors would result in the same level of uncertainty. We expect that our technique will become even more useful as (1) better kinematic constraints become available at larger distances and (2) cosmological simulations provide even more faithful representations of the observable Universe.
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  • 90
    Publication Date: 2016-07-21
    Description: We present new observations of the galaxy cluster 3C 129 obtained with the Sardinia Radio Telescope in the frequency range 6000–7200 MHz, with the aim to image the large-angular-scale emission at high-frequency of the radio sources located in this cluster of galaxies. The data were acquired using the recently commissioned ROACH2-based backend to produce full-Stokes image cubes of an area of 1° x 1° centred on the radio source 3C 129. We modelled and deconvolved the telescope beam pattern from the data. We also measured the instrumental polarization beam patterns to correct the polarization images for off-axis instrumental polarization. Total intensity images at an angular resolution of 2.9 arcmin were obtained for the tailed radio galaxy 3C 129 and for 13 more sources in the field, including 3C 129.1 at the galaxy cluster centre. These data were used, in combination with literature data at lower frequencies, to derive the variation of the synchrotron spectrum of 3C 129 along the tail of the radio source. If the magnetic field is at the equipartition value, we showed that the lifetimes of radiating electrons result in a radiative age for 3C 129 of t syn ~= 267 ± 26 Myr. Assuming a linear projected length of 488 kpc for the tail, we deduced that 3C 129 is moving supersonically with a Mach number of M  =  v gal / c s  = 1.47. Linearly polarized emission was clearly detected for both 3C 129 and 3C 129.1. The linear polarization measured for 3C 129 reaches levels as high as 70 per cent in the faintest region of the source where the magnetic field is aligned with the direction of the tail.
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  • 91
    Publication Date: 2016-07-21
    Description: Supernova remnants are believed to be the main sources of galactic cosmic rays (CR). Within this framework, particles are accelerated at supernova remnant shocks and then released in the interstellar medium. The mechanism through which CRs are released and the way in which they propagate still remain open issues. The main difficulty is the high non-linearity of the problem: CRs themselves excite the magnetic turbulence that confines them close to their sources. We solve numerically the coupled differential equations describing the evolution in space and time of the escaping particles and of the waves generated through the CR streaming instability. The warm ionized and warm neutral phases of the interstellar medium are considered. These phases occupy the largest fraction of the disc volume, where most supernovae explode, and are characterized by the significant presence of neutral particles. The friction between those neutrals and ions results in a very effective wave damping mechanism. It is found that streaming instability affects the propagation of CRs even in the presence of ion-neutral friction. The diffusion coefficient can be suppressed by more than a factor of ~2 over a region of few tens of pc around the remnant. The suppression increases for smaller distances. The propagation of 10 GeV particles is affected for several tens of kiloyears after escape, while 1 TeV particles are affected for few kiloyears. This might have a great impact on the interpretation of gamma-ray observations of molecular clouds located in the vicinity of supernova remnants.
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  • 92
    Publication Date: 2016-07-22
    Description: We have performed very large and high-resolution cosmological hydrodynamic simulations in order to investigate detectability of nebular lines in the rest-frame ultraviolet (UV) to optical wavelength range from galaxies at z 〉 7. We find that the expected line fluxes are very well correlated with the apparent UV magnitudes. The C  iv 1549 Å and C  iii ] 1909 Å lines of galaxies brighter than 26 AB magnitudes are detectable with current facilities such as the Very Large Telescope (VLT) XShooter and the Keck Multi-Object Spectrometer for Infra-Red Exploration (MOSFIRE). Metal lines such as C  iv 1549 Å, C  iii ] 1909 Å, [O  ii ] 3727 Å and [O  iii ] 4959/5007 Å are good targets for spectroscopic observation with the Thirty-Metre Telescope ( TMT ), European Extremely Large Telescope ( E-ELT ), Giant Magellan Telescope ( GMT ) and James Webb Space Telescope ( JWST ). We also expect Hα and Hβ lines to be detectable with these telescopes. Additionally, we predict the detectability of nebular lines for z 〉 10 galaxies, which will be found with JWST , the Wide-Field Infrared Survey Telescope ( WFIRST ) and First Light And Reionization Explorer ( FLARE ) (11 ≤ z ≤ 15). We conclude that the C  iv 1549 Å, C  iii ] 1909 Å, [O  iii ] 4959/5007 Å and Hβ lines from even z ~15 galaxies could be strong targets for TMT , E-ELT and JWST . We also find that magnification by gravitational lensing is of great help in detecting such high- z galaxies. According to our model, the C  iii ] 1909 Å line in z 〉 9 galaxy candidates is detectable even using current facilities.
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  • 93
  • 94
    Publication Date: 2016-07-22
    Description: In the context of the ASAI (Astrochemical Surveys At IRAM) project, we carried out an unbiased spectral survey in the millimetre window towards the well known low-mass Class I source SVS13-A. The high sensitivity reached (3–12 mK) allowed us to detect at least six HDO broad (full width at half-maximum ~4–5 km s –1 ) emission lines with upper level energies up to E u = 837 K. A non-local thermodynamic equilibrium Large Velocity Gradient (LVG) analysis implies the presence of very hot (150–260 K) and dense (≥3  x  10 7  cm –3 ) gas inside a small radius (~25 au) around the star, supporting, for the first time, the occurrence of a hot corino around a Class I protostar. The temperature is higher than expected for water molecules are sublimated from the icy dust mantles (~100 K). Although we cannot exclude we are observing the effects of shocks and/or winds at such small scales, this could imply that the observed HDO emission is tracing the water abundance jump expected at temperatures ~220–250 K, when the activation barrier of the gas phase reactions leading to the formation of water can be overcome. We derive X ( HDO ) ~ 3  x  10 –6 , and a H 2 O deuteration ≥1.5  x  10 –2 , suggesting that water deuteration does not decrease as the protostar evolves from the Class 0 to the Class I stage.
    Print ISSN: 1745-3925
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  • 95
    Publication Date: 2016-07-22
    Description: Evidence for the presence of quasi-periodic oscillations (QPOs) in the optical polarization of the blazar PKS 2155–304, during a period of enhanced gamma-ray brightness, is presented. The periodogram of the polarized flux revealed the existence of a prominent peak at T ~ 13 min, detected at 〉99.7 per cent significance, and T ~ 30 min, which was nominally significant at 〉99 per cent. This is the first evidence of QPOs in the polarization of an active galactic nucleus, potentially opening up a new avenue of studying this phenomenon.
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  • 96
    Publication Date: 2016-07-25
    Description: The modified dynamical equation of motions obtained by means of topological torsion currents predicts a so-far unforeseen anomalous acceleration detected in spacecrafts during close planetary flybys in retrograde direction, and a null-effect when spacecrafts approach the planet in the posigrade direction with respect to the planetary sense of rotation.
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  • 97
    Publication Date: 2016-07-25
    Description: 1H 0707–495 is the most convincing example of a supermassive black hole with an X-ray spectrum being dominated by extremely smeared, relativistic reflection, with the additional requirement of strongly supersolar iron abundance. However, here we show that the iron features in its 2–10 keV spectrum are rather similar to the archetypal wind dominated source, PDS 456. We fit all the 2–10 keV spectra from 1H 0707–495 using the same wind model as used for PDS 456, but viewed at higher inclination so that the iron absorption line is broader but not so blueshifted. This gives a good overall fit to the data from 1H 0707–495, and an extrapolation of this model to higher energies also gives a good match to the NuSTAR data. Small remaining residuals indicate that the iron line emission is stronger than in PDS 456. This is consistent with the wider angle wind expected from a continuum-driven wind from the super-Eddington mass accretion rate in 1H 0707–495, and/or the presence of residual reflection from the underlying disc though the presence of the absorption line in the model removes the requirement for highly relativistic smearing, and highly supersolar iron abundance. We suggest that the spectrum of 1H 0707–495 is sculpted more by absorption in a wind than by extreme relativistic effects in strong gravity.
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  • 98
    Publication Date: 2016-07-25
    Description: Equations of secular dynamics for stellar quadruple systems in 2+2 hierarchy are formulated. Non-singular, angular momentum and Laplace vector variables are used to describe orbital evolution of both inner and outer orbits. Given a typical wide separation of the binaries in these systems, gravitational interactions are truncated at the octupole approximation. Secular equations are propagated numerically and the results compared to the complete numerical integration on a long time-scale. Our basic formulation uses a point-mass model, but we also extend it by including the simplest description of the quadrupole interaction among the components of close (inner) binaries. Evolution of orbital planes of the binaries is discussed analytically in a simplified model and numerically using a more complete model. Maximum angular separation of the two orbital planes reaches only 20–40 per cent of the simple geometric maximum value for low-eccentricity cases with small inclination with respect to the orbital plane of the relative motion. This may be a pre-requisite for occurrence of quadruple systems with both binaries showing eclipses. However, statistical occurrence of eclipses at any time for a synthetic population of quadruples with initially isotropic distribution of orbital planes is about equal to the model where the orbits do not evolve due to gravitational interactions. We also show that the model is potentially suitable for long-term studies of the initial evolutionary tracks of the 2 + 2 quadruple systems.
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  • 99
    Publication Date: 2016-07-25
    Description: The rotational fission of asteroids has been studied previously with simplified models restricted to planar motion. However, the observed physical configuration of contact binaries leads one to conclude that most of them are not in a planar configuration and hence would not be restricted to planar motion once they undergo rotational fission. This motivated a study of the evolution of initially non-planar binaries created by fission. Using a two-ellipsoid model, we performed simulations taking only gravitational interactions between components into account. We simulate 91 different initial inclinations of the equator of the secondary body for 19 different mass ratios. After disruption, the binary system dynamics are chaotic, as predicted from theory. Starting the system in a non-planar configuration leads to a larger energy and enhanced coupling between the rotation state of the smaller fissioned body and the evolving orbital system, and enables re-impact to occur. This leads to differences with previous planar studies, with collisions and secondary spin fission occurring for all mass ratios with inclinations 0 ≥ 40 o , and mimics a Lidov–Kozai mechanism. Out of 1729 studied cases, we found that ~14 per cent result in secondary fission, ~25 per cent result in collisions and ~6 per cent have lifetimes longer than 200 yr. In Jacobson & Scheeres stable binaries only formed in cases with mass ratios q  〈 0.20. Our results indicate that it should be possible to obtain a stable binary with the same mechanisms for cases with mass ratios larger than this limit, but that the system should start in a non-planar configuration.
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  • 100
    Publication Date: 2016-07-25
    Description: Recent Spitzer /InfraRed Array Camera (IRAC) photometric observations have revealed that rest-frame optical emission lines contribute significantly to the broad-band fluxes of high-redshift galaxies. Specifically, in the narrow redshift range z  ~ 5.1–5.4 the [3.6]–[4.5] colour is expected to be very red, due to contamination of the 4.5 μm band by the dominant Hα line, while the 3.6 μm filter is free of nebular emission lines. We take advantage of new reductions of deep Spitzer /IRAC imaging over the Great Observatories Origins Deep Survey-North+South fields (Labbé et al. 2015 ) to obtain a clean measurement of the mean Hα equivalent width (EW) from the [3.6]–[4.5] colour in the redshift range z = 5.1–5.4. The selected sources either have measured spectroscopic redshifts (13 sources) or lie very confidently in the redshift range z = 5.1–5.4 based on the photometric redshift likelihood intervals (11 sources). Our z phot = 5.1–5.4 sample and z spec = 5.10–5.40 spectroscopic sample have a mean [3.6]–[4.5] colour of 0.31 ± 0.05 and 0.35 ± 0.07 mag, implying a rest-frame EW (Hα+[N ii ]+[S ii ]) of 665 ± 53 and 707 ± 74 Å, respectively, for sources in these samples. These values are consistent albeit slightly higher than derived by Stark et al. at z  ~ 4, suggesting an evolution to higher values of the Hα+[N ii ]+[S ii ] EW at z  〉 2. Using the 3.6 μm band, which is free of emission line contamination, we perform robust spectral energy distribution fitting and find a median specific star formation rate of sSFR = $17_{-5}^{+2}$ Gyr –1 , $7_{-2}^{+1}\times$ higher than at z  ~ 2. We find no strong correlation (〈2) between the Hα+[N ii ]+[S ii ] EW and the stellar mass of sources. Before the advent of JWST , improvements in these results will come through an expansion of current spectroscopic samples and deeper Spitzer /IRAC measurements.
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