ALBERT

Description: We exploit wide-field Ly α imaging with Subaru to probe the environment around TN J1338–1942, a powerful radio galaxy with a 〉 100 kpc Ly α halo at z  = 4.11. We used a sample of Ly α emitters (LAEs) down to log ( L Lyα [ erg s –1 ]) ~ 42.8 to measure the galaxy density around TN J1338–1942, compared to a control sample from a blank field taken with the same instrument. We found that TN J1338–1942 resides in a region with a peak overdensity of LAE  = 2.8 ± 0.5 on scales of 8 h – 1 Mpc (on the sky) and 112 h – 1 Mpc (line of sight) in comoving coordinates. Adjacent to this overdensity, we found a strong underdensity where virtually no LAEs are detected. We used a semi-analytical model of LAEs derived from the Millennium Simulation to compare our results with theoretical predictions. While the theoretical density distribution is consistent with the blank field, overdense regions such as that around TN J1338–1942 are very rare, with a number density of 6.4 x 10 – 8 Mpc – 3 (comoving), corresponding to the densest 〈0.4 percentile at z ~= 4.1. We also found that the Ly α luminosity function in the TN J1338–1942 field differs from that in the blank field: the number of bright LAEs (log ( L Lyα [ erg s – 1 ]) 43.3) is enhanced, while the number of fainter LAEs is relatively suppressed. These results suggest that some powerful radio galaxies associated with Ly α nebulae reside in extreme overdensities on ~3–6 Mpc scales, where star formation and AGN activity may be enhanced via frequent galaxy mergers or high rates of gas accretion from the surroundings.

Description: We use the galform semi-analytical model to study high-density regions traced by radio galaxies and quasars at high redshifts. We explore the impact that baryonic physics has upon the properties of galaxies in these environments. Star-forming emission-line galaxies (Ly α and H α emitters) are used to probe the environments at high redshifts. Radio galaxies are predicted to be hosted by more massive haloes than quasars, and this is imprinted on the amplitude of galaxy overdensities and cross-correlation functions. We find that Ly α radiative transfer and active galactic nucleus feedback indirectly affect the clustering on small scales and also the stellar masses, star formation rates and gas metallicities of galaxies in dense environments. We also investigate the relation between protoclusters associated with radio galaxies and quasars, and their present-day cluster descendants. The progenitors of massive clusters associated with radio galaxies and quasars allow us to determine an average protocluster size in a simple way. Overdensities within the protoclusters are found to correlate with the halo descendant masses. We present scaling relations that can be applied to observational data. By computing projection effects due to the wavelength resolution of modern spectrographs and narrow-band filters, we show that the former have enough spectral resolution to map the structure of protoclusters, whereas the latter can be used to measure the clustering around radio galaxies and quasars over larger scales to determine the mass of dark matter haloes hosting them.

Description: We present a survey of z ~ 3 Lyα emitters (LAEs) within the fields of the VLT Lyman break galaxies (LBG) redshift survey. The data encompass five independent survey fields co-spatial with spectroscopic LBG data and covering a larger total area than previously analysed for LAE number counts and clustering. This affords an improved analysis over previous work by minimizing the effects of cosmic variance and allowing the cross-clustering analysis of LAEs and LBGs. Our photometric sample consists of 600 LAE candidates, over an area of 1.07 deg 2 , with equivalent widths of 65 Å and a flux limit of 2  x  10 –17  erg cm –2  s –1 . From spectroscopic follow-up, we measured a success rate of 78 ± 18 per cent. We find the R -band continuum luminosity function to be ~10 times lower than the luminosity function of LBGs at this redshift, consistent with previous studies. Exploiting the large area of the survey, we estimate the LAE auto-correlation function and find a clustering length of r 0  = 2.86 ± 0.33 h –1  Mpc, low compared to the z ~ 3 LBG population, but somewhat higher than previous LAE measurements. This corresponds to a median halo mass of M DM  = 10 11.0±0.3 h –1  M . We present an analysis of clustering length versus continuum magnitude and find that the measurements for LAEs and LBGs are consistent at faint magnitudes. Our combined data set of LAEs and LBGs allows us to measure, for the first time, the LBG–LAE cross-correlation, finding a clustering length of r 0  = 3.29 ± 0.57 h –1  Mpc and a LAE halo mass of 10 11.1±0.4 h –1 M . Overall, we conclude that LAEs inhabit primarily low-mass haloes, but form a relatively small proportion of the galaxy population found in such haloes.

Description: We make use of a semi-analytical model of galaxy formation to investigate the origin of the observed correlation between [α/Fe] abundance ratios and stellar mass in elliptical galaxies. We implement a new galaxy-wide stellar initial mass function (IMF; top-heavy integrated galaxy initial mass function, TH-IGIMF) in the semi-analytic model SAG (acronym for semi-analytic galaxies) and evaluate its impact on the chemical evolution of galaxies. The star formation rate (SFR) dependence of the slope of the TH-IGIMF is found to be key to reproducing the correct [α/Fe]–stellar mass relation. Massive galaxies reach higher [α/Fe] abundance ratios because they are characterized by more top-heavy IMFs as a result of their higher SFR. As a consequence of our analysis, the value of the minimum embedded star cluster mass and of the slope of the embedded cluster mass function, which are free parameters involved in the TH-IGIMF theory, are found to be as low as 5 and 2 M , respectively. A mild downsizing trend is present for galaxies generated assuming either a universal IMF or a variable TH-IGIMF. We find that, regardless of galaxy mass, older galaxies (with formation redshifts 2) are formed in shorter time-scales (2 Gyr), thus achieving larger [α/Fe] values. Hence, the time-scale of galaxy formation alone cannot explain the slope of the [α/Fe]–galaxy mass relation, but is responsible for the big dispersion of [α/Fe] abundance ratios at fixed stellar mass. We further test the hypothesis of a TH-IGIMF in elliptical galaxies by looking into mass-to-light ratios, and luminosity functions. Models with a TH-IGIMF are also favoured by these constraints. In particular, mass-to-light ratios agree with observed values for massive galaxies while being overpredicted for less massive ones; this overprediction is present regardless of the IMF considered.

Description: Galaxy surveys targeting emission lines are characterizing the evolution of star-forming galaxies, but there is still little theoretical progress in modelling their physical properties. We predict nebular emission from star-forming galaxies within a cosmological galaxy formation model. Emission lines are computed by combining the semi-analytical model sag with the photoionization code mappings-iii . We characterize the interstellar medium of galaxies by relating the ionization parameter of gas in galaxies to their cold gas metallicity, obtaining a reasonable agreement with the observed Hα, [O ii ] 3727, [O iii ] 5007 luminosity functions, and the BPT diagram for local star-forming galaxies. The average ionization parameter is found to increase towards low star formation rates and high redshifts, consistent with recent observational results. The predicted link between different emission lines and their associated star formation rates is studied by presenting scaling relations to relate them. Our model predicts that emission-line galaxies have modest clustering bias, and thus reside in dark matter haloes of masses below M halo 10 12 [ h –1 M ]. Finally, we exploit our modelling technique to predict galaxy number counts up to z ~ 10 by targeting far-infrared emission lines detectable with submillimetre facilities.

Description: Ischia, a volcanic island located 18 miles SW of Naples (Southern Italy), is a densely populated active caldera that last erupted in ad 1302. Melt inclusions in phenocrysts of the Vateliero and Cava Nocelle shoshonite–latite eruptive products (6th to 4th centuries bc ) constrain the structure and nature of the Ischia deep magmatic feeding system. Their geochemical characteristics make Ischia a natural borehole for probing the physico-chemical conditions of magma generation in mantle contaminated by slab-derived fluids or melts, largely dominated by CO 2 . Volatile concentrations in olivine-hosted melt inclusions require gas–melt equilibria at between 3 and 18 km depth. In agreement with what has already been demonstrated at the other neighboring Neapolitan volcanoes (Procida, Campi Flegrei caldera and Somma–Vesuvius volcanic complex), a major crystallization depth at 8–10 km has been identified. The analyzed melt inclusions provide clear evidence for CO 2 -dominated gas fluxing and consequent dehydration of magma batches stagnating at crustal discontinuities. Gas fluxing is further supported by selective enrichment in K owing to fluid-transfer during magma differentiation. This takes place under oxidized conditions (Fe 3+ /Fe ≥ 0·3) that can be fixed by an equimolar proportion of divalent and trivalent iron in the melt if post-entrapment crystallization of the host olivine is discarded. The melt inclusion data, together with data from the literature for other Neapolitan volcanoes, show that magmatism and volcanism in the Neapolitan area, despite differences in composition and eruption dynamics, are closely linked to supercritical CO 2 -rich fluids. These fluids are produced by devolatilization of subducting terrigenous–pelagic metasediments and infiltrate the overlying mantle wedge, generate magmas and control their ascent up to eruption. Geochemical characteristics of Ischia and the other Neapolitan volcanoes reveal that the extent of fluid or melt contamination of the pre-subduction asthenospheric mantle wedge was similar among these volcanoes. However, differences in the isotopic compositions of the erupted magmas (more enriched in radiogenic Sr at Ischia, Campi Flegrei and Somma–Vesuvius with respect to Procida) and the amount of H 2 O in the plumbing system of these volcanoes (almost double at Ischia, Campi Flegrei and Somma–Vesuvius than at Procida) reflect the different flow-rates of deep slab-derived fluids or melts through the mantle wedge, which, in turn, control the amount of generated magma. The high bulk permeability of the lithosphere below Ischia, Campi Flegrei and Somma–Vesuvius, determined by the occurrence of intersecting NW–SE and NE–SW regional fault systems, favours fluid ascent and accumulation at crustal levels, with consequent larger magma production and storage than at Procida, located along the NE–SW system.

Description: Galaxy surveys aim to map the large-scale structure of the Universe and use redshift-space distortions to constrain deviations from general relativity and probe the existence of massive neutrinos. However, the amount of information that can be extracted is limited by the accuracy of theoretical models used to analyse the data. Here, by using the L-Galaxies semi-analytical model run over the Millennium-XXL N -body simulation, we assess the impact of galaxy formation on satellite kinematics and the theoretical modelling of redshift-space distortions. We show that different galaxy selection criteria lead to noticeable differences in the radial distributions and velocity structure of satellite galaxies. Specifically, whereas samples of stellar mass selected galaxies feature satellites that roughly follow the dark matter, emission line satellite galaxies are located preferentially in the outskirts of haloes and display net infall velocities. We demonstrate that capturing these differences is crucial for modelling the multipoles of the correlation function in redshift space, even on large scales. In particular, we show how modelling small-scale velocities with a single Gaussian distribution leads to a poor description of the measured clustering. In contrast, we propose a parametrization that is flexible enough to model the satellite kinematics and that leads to an accurate description of the correlation function down to sub-Mpc scales. We anticipate that our model will be a necessary ingredient in improved theoretical descriptions of redshift-space distortions, which together could result in significantly tighter cosmological constraints and a more optimal exploitation of future large data sets.

Description: In 1957, an invasive and highly defensive honey bee began to spread across Brazil. In the previous year, Brazilian researchers hoped to produce a subtropical-adapted honey bee by crossing local commercial honey bees (of European origin) with a South African honey bee subspecies (Apis mellifera scutellata; an A-lineage honey bee subspecies). The resulting cross—African hybrid honey bees (AHBs)—escaped from their enclosure and spread through the Americas. Today, AHB is the most common honey bee from Northern Argentina to the Southern United States. AHBs are much more likely to sting nest intruders than managed European-derived honey bee colonies. Previous studies have explored how genetic variation contributes to differences in defense response between European-derived honey bee and AHB. Although this work demonstrated very strong genetic effects on defense response, they have yet to pinpoint which genes influence variation in defense response within AHBs, specifically. We quantified defense response for 116 colonies in Brazil and performed pooled sequencing on the most phenotypically divergent samples. We identified 65 loci containing 322 genes that were significantly associated with defense response. Loci were strongly associated with metabolic function, consistent with previous functional genomic analyses of this phenotype. Additionally, defense-associated loci had nonrandom and unexpected patterns of admixture. Defense response was not simply the product of more A-lineage honey bee ancestry as previously assumed, but rather an interaction between A-lineage and European alleles. Our results suggest that a combination of A-lineage and European alleles play roles in defensive behavior in AHBs.