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  • 1
    Electronic Resource
    Electronic Resource
    An infrared flash contemporaneous with the γ-rays of GRB 041219a (2005)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 435 (2005), S. 181-184 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The explosion that results in a cosmic γ-ray burst (GRB) is thought to produce emission from two physical processes: the central engine gives rise to the high-energy emission of the burst through internal shocking, and the subsequent interaction of the flow with the external environment ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/nature03520
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    Paper (German National Licenses)
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  • 2
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    The chemistry of the most metal-rich damped Lyman {alpha} systems at z ~ 2 - II. Context with the Local Group (2015)
    Oxford University Press
    Details
    Publication Date: 2015-08-14
    Description: Using our sample of the most metal-rich damped Lyman α systems (DLAs) at z abs  ~ 2, and two literature compilations of chemical abundances in 341 DLAs and 2818 stars, we present an analysis of the chemical composition of DLAs in the context of the Local Group. The metal-rich sample of DLAs at z abs  ~ 2 probes metallicities as high as the Galactic disc and the most metal-rich dwarf spheroidals (dSphs), permitting an analysis of many elements typically observed in DLAs (Fe, Zn, Cr, Mn, Si, and S) in comparison to stellar abundances observed in the Galaxy and its satellites (in particular dSphs). Our main conclusions are: (1) non-solar [Zn/Fe] abundances in metal-poor Galactic stars and in dSphs over the full metallicity range probed by DLAs, suggest that Zn is not a simple proxy for Fe in DLAs and therefore not a suitable indicator of dust depletion. After correcting for dust depletion, the majority of DLAs have subsolar [Zn/Fe] similar to dSphs; (2) at [Fe/H] ~ –0.5, a constant [Mn/Fe]~–0.5 and near-solar [α/Fe] (requiring an assumption about dust depletion) are in better agreement with dwarf galaxies than Galactic disc stars; (3) [α/Zn] is usually solar or subsolar in DLAs. However, although low ratios of [α/Fe] are usually considered more ‘dwarf-like’ than ‘Milky Way-like’, subsolar [Zn/Fe] in Local Group dwarfs leads to supersolar [α/Zn] in the dSphs, in contrast with the DLAs. Therefore, whilst DLAs exhibit some similarities with the Local Group dwarf population, there are also notable differences.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 3
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    Using Machine Learning to classify the diffuse interstellar bands (2015)
    Oxford University Press
    Details
    Publication Date: 2015-05-30
    Description: Using over a million and a half extragalactic spectra from the Sloan Digital Sky Survey we study the correlations of the diffuse interstellar bands (DIBs) in the Milky Way. We measure the correlation between DIB strength and dust extinction for 142 DIBs using 24 stacked spectra in the reddening range E ( B  –  V ) 〈 0.2, many more lines than ever studied before. Most of the DIBs do not correlate with dust extinction. However, we find 10 weak and barely studied DIBs with correlations that are higher than 0.7 with dust extinction and confirm the high correlation of additional five strong DIBs. Furthermore, we find a pair of DIBs, 5925.9 and 5927.5 Å, which exhibits significant negative correlation with dust extinction, indicating that their carrier may be depleted on dust. We use Machine Learning algorithms to divide the DIBs to spectroscopic families based on 250 stacked spectra. By removing the dust dependence, we study how DIBs follow their local environment. We thus obtain six groups of weak DIBs, four of which are tightly associated with C 2 or CN absorption lines.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 4
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    Precise limits on cosmological variability of the fine-structure constant with zinc and chromium quasar absorption lines (2016)
    Oxford University Press
    Details
    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.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 5
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    MUSE searches for galaxies near very metal-poor gas clouds at z ~ 3: new constraints for cold accretion models (2016)
    Oxford University Press
    Details
    Publication Date: 2016-08-21
    Description: We report on the search for galaxies in the proximity of two very metal-poor gas clouds at z ~ 3 towards the quasar Q0956+122. With a 5-hour Multi-Unit Spectroscopic Explorer (MUSE) integration in a ~500 x 500 kpc 2 region centred at the quasar position, we achieve a ≥80 per cent complete spectroscopic survey of continuum-detected galaxies with m R ≤ 25 mag and Lyα emitters with luminosity L Lyα ≥ 3 x 10 41 erg s – 1 . We do not identify galaxies at the redshift of a z ~ 3.2 Lyman limit system (LLS) with log Z/Z = –3.35 ± 0.05, placing this gas cloud in the intergalactic medium or circumgalactic medium of a galaxy below our sensitivity limits. Conversely, we detect five Lyα emitters at the redshift of a pristine z ~ 3.1 LLS with log Z/Z ≤ –3.8, while ~0.4 sources were expected given the z ~ 3 Lyα luminosity function. Both this high detection rate and the fact that at least three emitters appear aligned in projection with the LLS suggest that this pristine cloud is tracing a gas filament that is feeding one or multiple galaxies. Our observations uncover two different environments for metal-poor LLSs, implying a complex link between these absorbers and galaxy haloes, which ongoing MUSE surveys will soon explore in detail. Moreover, in agreement with recent MUSE observations, we detected a ~ 90 kpc Lyα nebula at the quasar redshift and three Lyα emitters reminiscent of a ‘dark galaxy’ population.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 6
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    Nature and statistical properties of quasar associated absorption systems in the XQ-100 Legacy Survey (2016)
    Oxford University Press
    Details
    Publication Date: 2016-08-31
    Description: We statistically study the physical properties of a sample of narrow absorption line (NAL) systems looking for empirical evidences to distinguish between intrinsic and intervening NALs without taking into account any a priori definition or velocity cut-off. We analyse the spectra of 100 quasars with 3.5 〈 z em 〈 4.5, observed with X-shooter/Very Large Telescope in the context of the XQ-100 Legacy Survey. We detect an ~8 excess in the C iv number density within 10 000 km s – 1 of the quasar emission redshift with respect to the random occurrence of NALs. This excess does not show a dependence on the quasar bolometric luminosity and it is not due to the redshift evolution of NALs. It extends far beyond the standard 5000 km s – 1 cut-off traditionally defined for associated absorption lines. We propose to modify this definition, extending the threshold to 10 000 km s – 1 when weak absorbers (equivalent width 〈 0.2 Å) are also considered. We infer N v is the ion that better traces the effects of the quasar ionization field, offering the best statistical tool to identify intrinsic systems. Following this criterion, we estimate that the fraction of quasars in our sample hosting an intrinsic NAL system is 33 per cent. Lastly, we compare the properties of the material along the quasar line of sight, derived from our sample, with results based on close quasar pairs investigating the transverse direction. We find a deficiency of cool gas (traced by C ii ) along the line of sight connected to the quasar host galaxy, in contrast with what is observed in the transverse direction.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 7
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    A detailed study of the optical attenuation of gamma-ray bursts in the Swift era (2015)
    Oxford University Press
    Details
    Publication Date: 2015-04-10
    Description: We present optical and near-infrared (NIR) photometry of 28 gamma-ray bursts (GRBs) detected by the Swift satellite and rapidly observed by the Reionization and Transients Infrared/Optical (RATIR) camera. We compare the optical flux at fiducial times of 5.5 and 11 h after the high-energy trigger to that in the X-ray regime to quantify optical darkness. 46 ± 9 per cent (13/28) of all bursts in our sample and 55 ± 10 per cent (13/26) of long GRBs are optically dark, which is statistically consistently with previous studies. Fitting RATIR optical and NIR spectral energy distributions of 19 GRBs, most (6/7) optically dark GRBs either occur at high redshift ( z  〉 4.5) or have a high dust content in their host galaxies ( A V  〉 0.3). Performing Kolmogorov–Smirnov tests, we compare the RATIR sample to those previously presented in the literature, finding our distributions of redshift, optical darkness, host dust extinction and X-ray-derived column density to be consistent. The one reported discrepancy is with host galaxy dust content in the BAT6 sample, which appears inconsistent with our sample and other previous literature. Comparing X-ray-derived host galaxy hydrogen column densities to host galaxy dust extinction, we find that GRBs tend to occur in host galaxies with a higher metal-to-dust ratio than our own Galaxy, more akin to the Large and Small Magellanic Clouds. Finally, to mitigate time evolution of optical darkness, we measure β OX, rest at a fixed rest-frame time, t rest  = 1.5 h and fixed rest-frame energies in the X-ray and optical regimes. Choosing to evaluate optical flux at rest = 0.25 μm, we remove high redshift as a source of optical darkness, demonstrating that optical darkness must result from either high redshift, dust content in the host galaxy along the GRB sight line, or a combination of the two.
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    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 8
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    The first ultraviolet quasar-stacked spectrum at z ~= 2.4 from WFC3 (2015)
    Oxford University Press
    Details
    Publication Date: 2015-04-15
    Description: The ionizing continuum from active galactic nuclei is fundamental for interpreting their broad emission lines and understanding their impact on the surrounding gas. Furthermore, it provides hints on how matter accretes on to supermassive black holes. Using Hubble Space Telescope 's Wide Field Camera 3, we have constructed the first stacked ultraviolet (rest-frame wavelengths 600–2500 Å) spectrum of 53 luminous quasars at z ~= 2.4, with a state-of-the-art correction for the intervening Lyman forest and Lyman continuum absorption. The continuum slope ( $f_\nu \propto \nu ^{\alpha _\nu }$ ) of the full sample shows a break at ~912  Å with spectral index α = –0.61 ± 0.01 at 〉 912  Å and a softening at shorter wavelengths (α = –1.70 ± 0.61 at ≤ 912  Å). Our analysis proves that a proper intergalactic medium absorption correction is required to establish the intrinsic continuum emission of quasars. We interpret our average ultraviolet spectrum in the context of photoionization, accretion disc models, and quasar contribution to the ultraviolet background. We find that observed broad line ratios are consistent with those predicted assuming an ionizing slope of α ion  = –2.0, similar to the observed ionizing spectrum in the same wavelength range. The continuum break and softening are consistent with accretion disc plus X-ray corona models when black hole spin is taken into account. Our spectral energy distribution yields a 30 per cent increase to previous estimates of the specific quasar emissivity, such that quasars may contribute significantly to the total specific Lyman limit emissivity estimated from the Lyα forest at z  〈 3.2.
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    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 9
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    The neutral hydrogen cosmological mass density at z = 5 (2015)
    Oxford University Press
    Details
    Publication Date: 2015-07-04
    Description: We present the largest homogeneous survey of z  〉 4.4 damped Lyα systems (DLAs) using the spectra of 163 QSOs that comprise the Giant Gemini GMOS (GGG) survey. With this survey we make the most precise high-redshift measurement of the cosmological mass density of neutral hydrogen, $\Omega_{\rm H\,{\small i}}$ . At such high redshift, important systematic uncertainties in the identification of DLAs are produced by strong intergalactic medium absorption and QSO continuum placement. These can cause spurious DLA detections, result in real DLAs being missed or bias the inferred DLA column density distribution. We correct for these effects using a combination of mock and higher resolution spectra, and show that for the GGG DLA sample the uncertainties introduced are smaller than the statistical errors on $\Omega_{\rm H\,{\small i}}$ . We find $\rm \Omega _{\rm H\,\small {I}}=0.98^{+0.20}_{-0.18}\times 10^{-3}$ at 〈 z 〉 = 4.9, assuming a 20 per cent contribution from lower column density systems below the DLA threshold. By comparing to literature measurements at lower redshifts, we show that $\Omega_{\rm H\,{\small i}}$ can be described by the functional form $\Omega _{\rm H\,\small {I}}(z)\propto (1+z)^{0.4}$ . This gradual decrease from z  = 5 to 0 is consistent with the bulk of H i gas being a transitory phase fuelling star formation, which is continually replenished by more highly ionized gas from the intergalactic medium and from recycled galactic winds.
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    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 10
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    Using Machine Learning to classify the diffuse interstellar bands (2015)
    Oxford University Press
    Details
    Publication Date: 2015-06-12
    Description: Using over a million and a half extragalactic spectra from the Sloan Digital Sky Survey we study the correlations of the diffuse interstellar bands (DIBs) in the Milky Way. We measure the correlation between DIB strength and dust extinction for 142 DIBs using 24 stacked spectra in the reddening range E ( B  –  V ) 〈 0.2, many more lines than ever studied before. Most of the DIBs do not correlate with dust extinction. However, we find 10 weak and barely studied DIBs with correlations that are higher than 0.7 with dust extinction and confirm the high correlation of additional five strong DIBs. Furthermore, we find a pair of DIBs, 5925.9 and 5927.5 Å, which exhibits significant negative correlation with dust extinction, indicating that their carrier may be depleted on dust. We use Machine Learning algorithms to divide the DIBs to spectroscopic families based on 250 stacked spectra. By removing the dust dependence, we study how DIBs follow their local environment. We thus obtain six groups of weak DIBs, four of which are tightly associated with C 2 or CN absorption lines.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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