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  • 1
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    Far-reaching dust distribution in galaxy discs (2016)
    Oxford University Press
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    Publication Date: 2016-08-03
    Description: In most studies of dust in galaxies, dust is only detected from its emission to approximately the optical radius of the galaxy. By combining the signal of 110 spiral galaxies observed as part of the Herschel Reference Survey, we are able to improve our sensitivity by an order of magnitude over that for a single object. Here we report the direct detection of dust from its emission that extends out to at least twice the optical radius. We find that the distribution of dust is consistent with an exponential at all radii with a gradient of ~–1.7 dex  $R_{25}^{-1}$ . Our dust temperature declines linearly from ~25 K in the centre to 15 K at R 25 from where it remains constant out to ~2.0  R 25 . The surface density of dust declines with radius at a similar rate to the surface density of stars but more slowly than the surface density of the star-formation rate. Studies based on dust extinction and reddening of high-redshift quasars have concluded that there are substantial amounts of dust in intergalactic space. By combining our results with the number counts and angular correlation function from the SDSS, we show that with Milky Way-type dust we can explain the reddening of the quasars by the dust within galactic discs alone. Given the uncertainties in the properties of any intergalactic dust, we cannot rule out its existence, but our results show that statistical investigations of the dust in galactic haloes that use the reddening of high-redshift objects must take account of the dust in galactic discs.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 2
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    From flux to dust mass: Does the grain-temperature distribution matter for estimates of cold dust masses in supernova remnants? (2015)
    Oxford University Press
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    Publication Date: 2015-04-12
    Description: The amount of dust estimated from infrared to sub-millimetre (submm) observations strongly depends on assumptions of different grain sizes, compositions and optical properties. Here we use a simple model of thermal emission from cold silicate/carbon dust at a range of dust grain temperatures and fit the spectral energy distribution (SED) of the Crab nebula as a test. This can lower the derived dust mass for the Crab by ~50 per cent and 30–40 per cent for astronomical silicates and amorphous carbon grains compared to recently published values (0.25 M -〉 0.12 M and 0.12 M -〉 0.072 M , respectively), but the implied dust mass can also increase by as much as almost a factor of 6 (0.25 M -〉 1.14 M and 0.12 M -〉 0.71 M ) depending on assumptions regarding the sizes/temperatures of the coldest grains. The latter values are clearly unrealistic due to the expected metal budget, though. Furthermore, we show by a simple numerical experiment that if a cold-dust component does have a grain-temperature distribution, it is almost unavoidable that a two-temperature fit will yield an incorrect dust mass estimate. But we conclude that grain temperatures is not a greater uncertainty than the often poorly constrained emissivities (i.e. material properties) of cosmic dust, although there is clearly a need for improved dust emission models. The greatest complication associated with deriving dust masses still arises in the uncertainty in the dust composition.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 3
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    Herschel-ATLAS: the surprising diversity of dust-selected galaxies in the local submillimetre Universe (2015)
    Oxford University Press
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    Publication Date: 2015-07-05
    Description: We present the properties of the first 250 μm blind sample of nearby galaxies (15 〈  D  〈 46 Mpc) containing 42 objects from the Herschel Astrophysical Terahertz Large Area Survey. Herschel's sensitivity probes the faint end of the dust luminosity function for the first time, spanning a range of stellar mass (7.4 〈  M *  〈 11.3 log 10 M ), star formation activity (–11.8 〈  SSFR  〈 –8.9 log 10 yr –1 ), gas fraction (3–96 per cent), and colour (0.6 〈 FUV– K S  〈 7.0 mag). The median cold dust temperature is 14.6 K, colder than in the Herschel Reference Survey (18.5 K) and Planck Early Release Compact Source Catalogue (17.7 K). The mean dust-to-stellar mass ratio in our sample is higher than these surveys by factors of 3.7 and 1.8, with a dust mass volume density of (3.7 ± 0.7)  x  10 5 M Mpc –3 . Counter-intuitively, we find that the more dust rich a galaxy, the lower its UV attenuation. Over half of our dust-selected sample are very blue in FUV– K S colour, with irregular and/or highly flocculent morphology; these galaxies account for only 6 per cent of the sample's stellar mass but contain over 35 per cent of the dust mass. They are the most actively star-forming galaxies in the sample, with the highest gas fractions and lowest UV attenuation. They also appear to be in an early stage of converting their gas into stars, providing valuable insights into the chemical evolution of young galaxies.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 4
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    H-ATLAS: estimating redshifts of Herschel sources from sub-mm fluxes (2013)
    Oxford University Press
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    Publication Date: 2013-10-12
    Description: Upon its completion, the Herschel Astrophysics Terahertz Large Area Survey (H-ATLAS) will be the largest sub-millimetre survey to date, detecting close to half-a-million sources. It will only be possible to measure spectroscopic redshifts for a small fraction of these sources. However, if the rest-frame spectral energy distribution (SED) of a typical H-ATLAS source is known, this SED and the observed Herschel fluxes can be used to estimate the redshifts of the H-ATLAS sources without spectroscopic redshifts. In this paper, we use a sub-set of 40 H-ATLAS sources with previously measured redshifts in the range 0.5 〈  z  〈 4.2 to derive a suitable average template for high-redshift H-ATLAS sources. We find that a template with two dust components ( T c = 23.9 K, T h = 46.9 K and ratio of mass of cold dust to mass of warm dust of 30.1) provides a good fit to the rest-frame fluxes of the sources in our calibration sample. We use a jackknife technique to estimate the accuracy of the redshifts estimated with this template, finding a root mean square of z /(1 +  z ) = 0.26. For sources for which there is prior information that they lie at z  〉 1, we estimate that the rms of z /(1 +  z ) = 0.12. We have used this template to estimate the redshift distribution for the sources detected in the H-ATLAS equatorial fields, finding a bimodal distribution with a mean redshift of 1.2, 1.9 and 2.5 for 250, 350 and 500 μm selected sources, respectively.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 5
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    Herschel-ATLAS: properties of dusty massive galaxies at low and high redshifts (2014)
    Oxford University Press
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    Publication Date: 2014-05-06
    Description: We present a comparison of the physical properties of a rest-frame 250-μm-selected sample of massive, dusty galaxies from 0 〈 z  〈 5.3. Our sample comprises 29 high-redshift submillimetre galaxies (SMGs) from the literature and 843 dusty galaxies at z  〈 0.5 from the Herschel -Astrophysical TeraHertz Large Area Survey (H-ATLAS), selected to have a similar stellar mass to the SMGs. The z  〉 1 SMGs have an average star formation rate (SFR) of $390^{+80}_{-70}\,$  M  yr –1 , which is 120 times that of the low-redshift sample matched in stellar mass to the SMGs (SFR = 3.3 ± 0.2 M  yr –1 ). The SMGs harbour a substantial mass of dust ( $1.2^{+0.3}_{-0.2}\times {10}^9\,$  M ), compared to (1.6 ± 0.1) 10 8  M for low-redshift dusty galaxies. At low redshifts, the dust luminosity is dominated by the diffuse interstellar medium, whereas a large fraction of the dust luminosity in SMGs originates from star-forming regions. At the same dust mass, SMGs are offset towards a higher SFR compared to the low-redshift H-ATLAS galaxies. This is not only due to the higher gas fraction in SMGs but also because they are undergoing a more efficient mode of star formation, which is consistent with their bursty star formation histories. The offset in SFR between SMGs and low-redshift galaxies is similar to that found in CO studies, suggesting that dust mass is as good a tracer of molecular gas as CO.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 6
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    The dust budget crisis in high-redshift submillimetre galaxies (2014)
    Oxford University Press
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    Publication Date: 2014-05-06
    Description: We apply a chemical evolution model to investigate the sources and evolution of dust in a sample of 26 high-redshift ( z  〉 1) submillimetre galaxies (SMGs) from the literature, with complete photometry from ultraviolet to the submillimetre. We show that dust produced only by low–intermediate-mass stars falls a factor 240 short of the observed dust masses of SMGs, the well-known ‘dust-budget crisis’. Adding an extra source of dust from supernovae can account for the dust mass in 19 per cent of the SMG sample. Even after accounting for dust produced by supernovae the remaining deficit in the dust mass budget provides support for higher supernova yields, substantial grain growth in the interstellar medium or a top-heavy IMF. Including efficient destruction of dust by supernova shocks increases the tension between our model and observed SMG dust masses. The models which best reproduce the physical properties of SMGs have a rapid build-up of dust from both stellar and interstellar sources and minimal dust destruction. Alternatively, invoking a top-heavy IMF or significant changes in the dust grain properties can solve the dust budget crisis only if dust is produced by both low-mass stars and supernovae and is not efficiently destroyed by supernova shocks.
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    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 7
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    The Herschel exploitation of local galaxy Andromeda (HELGA) - V. Strengthening the case for substantial interstellar grain growth (2014)
    Oxford University Press
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    Publication Date: 2014-08-25
    Description: In this paper, we consider the implications of the distributions of dust and metals in the disc of M31. We derive mean radial dust distributions using a dust map created from Herschel images of M31 sampling the entire far-infrared peak. Modified blackbodies are fit to approximately 4000 pixels with a varying, as well as a fixed, dust emissivity index (β). An overall metal distribution is also derived using data collected from the literature. We use a simple analytical model of the evolution of the dust in a galaxy with dust contributed by stellar sources and interstellar grain growth, and fit this model to the radial dust-to-metals distribution across the galaxy. Our analysis shows that the dust-to-gas gradient in M31 is steeper than the metallicity gradient, suggesting interstellar dust growth is (or has been) important in M31. We argue that M31 helps build a case for cosmic dust in galaxies being the result of substantial interstellar grain growth, while the net dust production from stars may be limited. We note, however, that the efficiency of dust production in stars, e.g. in supernovae ejecta and/or stellar atmospheres, and grain destruction in the interstellar medium may be degenerate in our simple model. We can conclude that interstellar grain growth by accretion is likely at least as important as stellar dust production channels in building the cosmic dust component in M31.
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    Topics: Physics
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  • 8
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    An empirical determination of the dust mass absorption coefficient, {kappa}d, using the Herschel Reference Survey (2016)
    Oxford University Press
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    Publication Date: 2016-04-29
    Description: We use the published photometry and spectroscopy of 22 galaxies in the Herschel Reference Survey to determine that the value of the dust mass absorption coefficient d at a wavelength of 500 μm is $\kappa _{500} = 0.051^{+0.070}_{-0.026}\,{\rm m^{2}\,kg^{-1}}$ . We do so by taking advantage of the fact that the dust-to-metals ratio in the interstellar medium of galaxies appears to be constant. We argue that our value for d supersedes that of James et al. – who pioneered this approach for determining d – because we take advantage of superior data, and account for a number of significant systematic effects that they did not consider. We comprehensively incorporate all methodological and observational contributions to establish the uncertainty on our value, which represents a marked improvement on the oft-quoted ‘order-of-magnitude’ uncertainty on d . We find no evidence that the value of d differs significantly between galaxies, or that it correlates with any other measured or derived galaxy properties. We note, however, that the availability of data limits our sample to relatively massive (10 9.7  〈  M *  〈 10 11.0 M ), high metallicity (8.61 〈  $[ 12 + {\rm log}_{10} \frac{\rm O}{\rm H} ]$  〈 8.86) galaxies; future work will allow us to investigate a wider range of systems.
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    Topics: Physics
    Published by Oxford University Press
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  • 9
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    The dust mass in Cassiopeia A from a spatially resolved Herschel analysis (2016)
    Oxford University Press
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    Publication Date: 2016-12-21
    Description: Theoretical models predict that core-collapse supernovae (CCSNe) can be efficient dust producers (0.1–1.0 M ), potentially accounting for most of the dust production in the early Universe. Observational evidence for this dust production efficiency is however currently limited to only a few CCSN remnants (e.g. SN 1987A, Crab nebula). In this paper, we revisit the dust mass produced in Cassiopeia A (Cas A), a ~330-yr old O-rich Galactic supernova remnant (SNR) embedded in a dense interstellar foreground and background. We present the first spatially resolved analysis of Cas A based on Spitzer and Herschel infrared and submillimetre data at a common resolution of ~0.6 arcmin for this 5 arcmin diameter remnant following a careful removal of contaminating line emission and synchrotron radiation. We fit the dust continuum from 17 to 500 μm with a four-component interstellar medium and supernova (SN) dust model. We find a concentration of cold dust in the unshocked ejecta of Cas A and derive a mass of 0.3–0.5 M of silicate grains freshly produced in the SNR, with a lower limit of ≥0.1–0.2 M . For a mixture of 50 per cent of silicate-type grains and 50 per cent of carbonaceous grains, we derive a total SN dust mass between 0.4 and 0.6 M . These dust mass estimates are higher than from most previous studies of Cas A and support the scenario of SN-dominated dust production at high redshifts. We furthermore derive an interstellar extinction map for the field around Cas A which towards Cas A gives average values of A V  = 6–8 mag, up to a maximum of A V = 15 mag.
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    Topics: Physics
    Published by Oxford University Press
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  • 10
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    STAG3 is a strong candidate gene for male infertility (2014)
    Oxford University Press
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    Publication Date: 2014-06-10
    Description: Oligo- and azoospermia are severe forms of male infertility. However, known genetic factors account only for a small fraction of the cases. Recently, whole-exome sequencing in a large consanguineous family with inherited premature ovarian failure (POF) identified a homozygous frameshift mutation in the STAG3 gene leading to a premature stop codon. STAG3 encodes a meiosis-specific subunit of the cohesin complex, a large proteinaceous ring with DNA-entrapping ability that ensures sister chromatid cohesion and enables correct synapsis and segregation of homologous chromosomes during meiosis. The pathogenicity of the STAG3 mutations was functionally validated with a loss-of-function mouse model for STAG3 in oogenesis. However, and since none of the male members of this family was homozygous for the mutant allele, we only could hypothesized its putative involvement in male infertility. In this report, we show that male mice devoid of Stag3 display a severe meiotic phenotype that includes a meiotic arrest at zygonema-like shortening of their chromosome axial elements/lateral elements, partial loss of centromeric cohesion at early prophase and maintenance of the ability to initiate but not complete RAD51- and DMC1-mediated double-strand break repair, demonstrating that STAG3 is a crucial cohesin subunit in mammalian gametogenesis and supporting our proposal that STAG3 is a strong candidate gene for human male infertility.
    Print ISSN: 0964-6906
    Electronic ISSN: 1460-2083
    Topics: Biology , Medicine
    Published by Oxford University Press
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