The dust obscuration bias in damped Lyman <i>α</i>systems

Vladilo, G.; Péroux, Céline

doi:10.1051/0004-6361:20041570

Cited by 85 publications

(151 citation statements)

References 65 publications

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“…Interestingly, the zinc and hydrogen column densities measured here place the DLA close to the observational limit proposed by Prantzos & Boissier (2000) beyond which the quasar would be too attenuated to be observable (see also Boissé et al 1998;Vladilo & Péroux 2005 Noterdaeme et al 2008) and in-between the values found in warm neutral gas in the Galactic disk and the halo (Welty et al 1999). Similar depletion patterns have been observed along gas-rich lines of sight through the SMC (Welty et al 2001).…”

Section: Metal and Dust Contentsupporting

confidence: 87%

Discovery of a compact gas-rich damped Lyman-αgalaxy atz = 2.2: evidence of a starburst-driven outflow

Noterdaeme

Laursen

Petitjean

et al. 2012

A&A

124

144

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We present the detection of Ly α, [O iii], and H α emission associated with an extremely strong damped Lyman-α (DLA) system (N(H i) = 10 22.10 cm −2 ) at z = 2.207 towards the quasar SDSS J113520.39−001053.56. This is the largest H i column density ever measured along a quasi-stellar object (QSO) line of sight, though typical of those often found in DLAs associated to gamma-ray bursts (GRBs). This absorption system can also be classified as an ultra-strong Mg ii system with W λ2796 , and is unresolved. From the H α line, we measure a significant star formation rate (SFR) ≈ 25 M yr −1 (uncorrected for dust). The shape of the Ly α line is double-peaked, which is the signature of a resonant scattering of Ly α photons, and the Ly α emission is spatially extended. More strikingly, the blue and red Ly α peaks arise from distinct regions extended over a few kpc on either side of the star-forming region. We propose that this is the consequence of a Ly α transfer in outflowing gas. The presence of starburst-driven outflows is also in agreement with the high SFR together with the small size and low mass of the galaxy (M vir ∼ 10 10 M ). By placing constraints on the stellar UV continuum luminosity of the galaxy, we estimate an age of at most a few 10 7 yr, again consistent with a recent starburst scenario. We interpret these data as the observation of a young, gas-rich, compact starburst galaxy, from which material is expelled through collimated winds powered by the vigorous star formation activity. We substantiate this picture by modelling the radiative transfer of Ly α photons in the galactic counterpart. Though our model (a spherical galaxy with bipolar outflowing jets) is a simplistic representation of the true gas distribution and velocity field, the agreement between the observed and simulated properties is particularly good (spectral shape and width of the Lyman-α emission, spatial configuration, escape fraction as well as absorption kinematics, H i column density, and dust reddening). Finally, we propose that selecting DLAs with very high H i column densities may be an efficient way of detecting star-forming galaxies at small impact parameters from the background QSO lines of sight.

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Section: Metal and Dust Contentsupporting

confidence: 87%

Discovery of a compact gas-rich damped Lyman-αgalaxy atz = 2.2: evidence of a starburst-driven outflow

Noterdaeme

Laursen

Petitjean

et al. 2012

A&A

124

144

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“…An additional possibility to explain the trend with metallicity is the well-known anti-correlation between metallicity and H i column density (Boissé et al 1998;Vladilo & Péroux 2005). As a result of this trend, DLA systems with high metallicity would experience more argon ionisation because they would have, on average, low H i selfshielding.…”

Section: Bias Effectsmentioning

confidence: 99%

The ESO UVES Advanced Data Products Quasar Sample – IV. On the deficiency of argon in DLA systems

Zafar¹,

Vladilo²,

Péroux³

et al. 2014

Monthly Notices of the Royal Astronomical Society

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In this work, we study argon abundances in the interstellar medium of high-redshift galaxies (2.0 z abs 4.2) detected as Damped Lyα absorbers (DLA) in the spectra of background quasars. We use high-resolution quasar spectra obtained from the ESO-UVES advanced data products (EUADP) database. We present 3 new measurements and 5 upper limits of Ar i. We further compiled DLAs/sub-DLA data from the literature with measurements available of argon and α-capture elements (S or Si), making up a total of 37 systems, i.e. the largest DLA argon sample investigated so far. We confirm that argon is generally deficient in DLAs, with a mean value [Ar/α] ≃ −0.4 ± 0.06 dex (standard error of the mean). The [Ar/α] ratios show a weak, positive trend with increasing H i column density and increasing absorption redshift, and a weak, negative trend with dust-free metallicity, [S/H]. Detailed analysis of the abundance ratios indicates that Ar i ionisation, rather than dust depletion or nucleosynthetic evolution, is responsible for the argon deficiency. Altogether, the observational evidence is consistent with a scenario of argon ionisation dominated by quasar metagalactic radiation modulated by local H i self-shielding inside the DLA host galaxies. Our measurements and limits of argon abundances suggest that the cosmic reionisation of He ii is completed above z ∼ 3, but more measurements at z abs > 3.5 are required to probe the final stages of this process of cosmic reionisation.

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“…However, this does not mean that such systems do not exist and an anti-correlation between absorber dust content and afterglow optical brightness should be checked. Indeed, the associated extinction will be high in these systems (Vladilo & Péroux 2005; see also Prochaska et al 2009) and their observation with high-resolution spectrographs, even with the advantage of fast response, possibly difficult. This is consistent with the findings of multi-colour photometry that a large fraction of bursts are dark because of high dust extinction in their hosts (Rol et al 2007;Jaunsen et al 2008;Tanvir et al 2008;Cenko et al 2009).…”

Section: Summary and Prospectsmentioning

confidence: 99%

Physical conditions in high-redshift GRB-DLA absorbers observed with VLT/UVES: implications for molecular hydrogen searches

Ledoux¹,

Vreeswijk

Smette³

et al. 2009

A&A

160

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Aims. We aim to understand the nature of the absorbing neutral gas in the galaxies hosting high-redshift long-duration gamma-ray bursts (GRBs) and to determine their physical conditions. Methods. A detailed analysis of high-quality VLT/UVES spectra of the optical afterglow of GRB 050730 and other Swift-era bursts is presented. Results. We report the detection of a significant number of previously unidentified allowed transition lines of Fe + , involving the fine structure of the ground term ( 6 D 7/2 , 6 D 5/2 , 6 D 3/2 , 6 D 1/2 ) and that of other excited levels ( 4 F 9/2 , 4 F 7/2 , 4 F 5/2 , 4 F 3/2 , 4 D 7/2 , 4 D 5/2 ), from the z abs = 3.969, log N(H 0 ) = 22.10, damped Lyman-α (DLA) system located in the host galaxy of GRB 050730. No molecular hydrogen (H 2 ) is detected down to a molecular fraction of log f < −8.0. We derive accurate metal abundances for Fe + , S + , N 0 , Ni + , and, for the first time in this system, Si + and Ar 0 . The absorption lines are best-fit as a single narrow velocity component at z abs = 3.96857. The time-dependent evolution of the observed Fe + energy-level populations is modelled by assuming the excitation mechanism is fluorescence following excitation by ultraviolet photons emitted by the afterglow of GRB 050730. This UV pumping model successfully reproduces the observations, yielding a total Fe + column density of log N = 15.49 ± 0.03, a burst/cloud distance (defined to the near-side of the cloud) of d = 440 ± 30 pc, and a linear cloud size of l = 520 +240 −190 pc. This application of our photoexcitation code demonstrates that burst/DLA distances can be determined without strong constraints on absorption-line variability provided enough energy levels are detected. From the cloud size, we infer a particle density of n H ≈ 5−15 cm −3 . Conclusions.We discuss these results in the context of no detections of H 2 and C i lines (with log N(C 0 )/N(S + ) < −3) in a sample of seven z > 1.8 GRB host galaxies observed with VLT/UVES. We show that the lack of H 2 can be explained by the low metallicities, [X/H] < −1, low depletion factors, and, at most, moderate particle densities of the systems. This points to a picture where GRB-DLAs typically exhibiting very high H 0 column densities are diffuse metal-poor atomic clouds with high kinetic temperatures, T kin > ∼ 1000 K, and large physical extents, l > ∼ 100 pc. The properties of GRB-DLAs observed at high spectral resolution towards bright GRB afterglows differ markedly from the high metal and dust contents of GRB-DLAs observed at lower resolution. This difference likely results from the effect of a bias, against systems of high metallicity and/or close to the GRB, due to dust obscuration in the magnitudelimited GRB afterglow samples observed with high-resolution spectrographs.

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The dust obscuration bias in damped Lyman αsystems

Cited by 85 publications

References 65 publications

Discovery of a compact gas-rich damped Lyman-αgalaxy atz = 2.2: evidence of a starburst-driven outflow

Discovery of a compact gas-rich damped Lyman-αgalaxy atz = 2.2: evidence of a starburst-driven outflow

The ESO UVES Advanced Data Products Quasar Sample – IV. On the deficiency of argon in DLA systems

Physical conditions in high-redshift GRB-DLA absorbers observed with VLT/UVES: implications for molecular hydrogen searches

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