2009A&A...506..661L


C.D.S. - SIMBAD4 rel 1.7 - 2019.11.15CET07:38:00

2009A&A...506..661L - Astronomy and Astrophysics, volume 506, 661-675 (2009/11-1)

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

LEDOUX C., VREESWIJK P.M., SMETTE A., FOX A.J., PETITJEAN P., ELLISON S.L., FYNBO J.P.U. and SAVAGLIO S.

Abstract (from CDS):

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.A detailed analysis of high-quality VLT/UVES spectra of the optical afterglow of GRB050730 and other Swift-era bursts is presented.We report the detection of a significant number of previously unidentified allowed transition lines of Fe+, involving the fine structure of the ground term (6D7/2, 6D5/2, 6D3/2, 6D1/2) and that of other excited levels (4F9/2, 4F7/2, 4F5/2, 4F3/2, 4D7/2, 4D5/2), from the z_ abs_=3.969, logN(H0)=22.10, damped Lyman-α (DLA) system located in the host galaxy of GRB050730. No molecular hydrogen (H2) is detected down to a molecular fraction of logf←8.0. We derive accurate metal abundances for Fe+, S+, N0, Ni+, and, for the first time in this system, Si+ and Ar0. The absorption lines are best-fit as a single narrow velocity component at zabs=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 GRB050730. This UV pumping model successfully reproduces the observations, yielding a total Fe+ column density of logN=15.49±0.03, a burst/cloud distance (defined to the near-side of the cloud) of d=440±30pc, and a linear cloud size of l=520+240–190pc. This application of our photo-excitation 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 nH≃5-15cm–3.We discuss these results in the context of no detections of H2 and CI lines (with log N(C0)/N(S+)←3) in a sample of seven z>1.8 GRB host galaxies observed with VLT/UVES. We show that the lack of H2 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 H0 column densities are diffuse metal-poor atomic clouds with high kinetic temperatures, Tkin>1000K, and large physical extents, l>100pc. 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 magnitude-limited GRB afterglow samples observed with high-resolution spectrographs.

Abstract Copyright:

Journal keyword(s): gamma rays: bursts - Galaxy: abundances - galaxies: ISM - galaxies: quasars: absorption lines - cosmology: observations

Errata: + corrigendum vol. 532, p. C3 (2011)

Simbad objects: 20

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Number of rows : 20

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2020
#notes
1 GRB 071031 gB 00 25 37.40 -58 03 33.9           ~ 138 0
2 GRB 070802 gB 02 27 35.91 -55 31 39.1           ~ 132 0
3 4C -02.19 QSO 05 01 12.80988366 -01 59 14.2562534   19.1 18.4 19.04   ~ 505 1
4 NAME LMC G 05 23 34.6 -69 45 22     0.4     ~ 14348 1
5 RMC 136 Cl* 05 38 42.396 -69 06 03.36   9.63 9.50     ~ 1677 2
6 QSO B1157+014 QSO 11 59 44.8277890111 +01 12 06.984367162   17.87 17.52     ~ 194 1
7 QSO B1209+0919 QSO 12 11 34.9529988214 +09 02 20.851330054   19.61 19.15     ~ 90 0
8 GRB 080607 gB 12 59 47.14 +15 55 09.6           ~ 202 0
9 GRB 060206 gB 13 31 43.420 +35 03 03.60   19.99 17.09     ~ 276 1
10 GRB 050730 gB 14 08 17.090 -03 46 18.90   20.32 17.68     ~ 276 1
11 GRB 080319B gB 14 31 41.04 +36 18 09.2           ~ 417 0
12 GRB 080310 gB 14 40 13.89 -00 10 30.4           ~ 155 0
13 GRB 060418 gB 15 45 42.600 -03 38 20.00 15.73 16.19 14.98     ~ 318 1
14 GRB 050401 gB 16 31 28.84 +02 11 14.5           ~ 295 0
15 GRB 080413A gB 19 09 11.73 -27 40 39.6           ~ 119 0
16 GRB 020813A gB 19 46 41.874 -19 36 04.81           ~ 281 1
17 GRB 050922C gB 21 09 33.000 -08 45 30.10 15.15 15.86 14.69     ~ 244 0
18 GRB 060607 gB 21 58 50.400 -22 29 46.70 18.49 16.67 15.09     ~ 250 1
19 GRB 050820A gB 22 29 38.110 +19 33 37.10 18.33 19.00 18.47     ~ 331 1
20 GRB 051111A gB 23 12 33.170 +18 22 28.80 19.77 20.08 19.50     ~ 183 1

    Equat.    Gal    SGal    Ecl

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2019.11.15-07:38:00

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