2015A&A...578L...5N


C.D.S. - SIMBAD4 rel 1.7 - 2019.12.07CET21:19:23

2015A&A...578L...5N - Astronomy and Astrophysics, volume 578, L5-5 (2015/6-1)

The elusive HI->H2 transition in high-z damped Lyman-α systems.

NOTERDAEME P., PETITJEAN P. and SRIANAND R.

Abstract (from CDS):

We study the H2 molecular content in high redshift damped Lyman-α systems (DLAs) as a function of the HI column density. We find a significant increase of the H2 molecular content around logN(HI)(cm–2)∼21.5-22, a regime unprobed until now in intervening DLAs, beyond which the majority of systems have logN(H2)>17. This is in contrast with lines of sight towards nearby stars, where such H2 column densities are always detected as soon as logN(HI)>20.7. This can qualitatively be explained by the lower average metallicity and possibly higher surrounding UV radiation in DLAs. However, unlike in the Milky Way, the overall molecular fractions remain modest, showing that even at a large N(HI) only a small fraction of overall HI is actually associated with the self-shielded H2 gas. Damped Lyman-α systems with very high-N(HI) probably arise along quasar lines of sight passing closer to the centre of the host galaxy where the gas pressure is higher. We show that the colour changes induced on the background quasar by continuum (dust) and line absorption (HI Lyman and H2 Lyman & Werner bands) in DLAs with logN(HI)∼22 and metallicity ∼1/10 solar is significant, but not responsible for the long-discussed lack of such systems in optically selected samples. Instead, these systems are likely to be found towards intrinsically fainter quasars that dominate the quasar luminosity function. Colour biasing should in turn be severe at higher metallicities.

Abstract Copyright:

Journal keyword(s): quasars: absorption lines - ISM: molecules

Simbad objects: 12

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Number of rows : 12

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 QSO B0027-1836 QSO 00 30 23.6257396463 -18 19 56.118776105   18.2 17.9     ~ 41 0
2 NAME SMC G 00 52 38.0 -72 48 01   2.79 2.2     ~ 9131 1
3 SDSS J015445.22+193515.8 QSO 01 54 45.2207756985 +19 35 15.905470906           ~ 6 0
4 NAME Magellanic Clouds GrG 03 00 -71.0           ~ 5399 1
5 GRB 121024A gB 04 41 53.30 -12 17 26.0           ~ 75 0
6 4C -02.19 QSO 05 01 12.80988366 -01 59 14.2562534   19.1 18.4 19.04   ~ 505 1
7 SDSS J081634.38+144612.4 QSO 08 16 34.3910998278 +14 46 12.475883677   21.91 20.39     ~ 28 0
8 QSO B1157+014 QSO 11 59 44.8277890111 +01 12 06.984367162   17.87 17.52     ~ 195 1
9 GRB 080607 gB 12 59 47.14 +15 55 09.6           ~ 202 0
10 SDSS J145646.48+160939.3 QSO 14 56 46.4827746733 +16 09 39.378002911   20.89 20.04     ~ 12 0
11 GRB 120815A gB 18 15 54.40 -52 07 29.0           ~ 58 0
12 SDSS J214043.01-032139.2 QSO 21 40 43.0140120857 -03 21 39.259765833           ~ 9 0

    Equat.    Gal    SGal    Ecl

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2019.12.07-21:19:23

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