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2003MNRAS.346..209L - Mon. Not. R. Astron. Soc., 346, 209-228 (2003/November-3)
The Very Large Telescope Ultraviolet and Visible Echelle Spectrograph survey for molecular hydrogen in high-redshift damped Lyman α systems.
LEDOUX C., PETITJEAN P. and SRIANAND R.
Abstract (from CDS):
In all of the systems, we measure metallicities relative to solar, [X/H] (with either X Zn, S or Si), and depletion factors of Fe, [X/Fe], supposedly on to dust grains, and compare the characteristics of our sample with those of the global population of DLA systems (60 systems in total). We find that there is a correlation between the metallicity and the depletion factor in both our sample and also the global population of DLA systems. Although H2 molecules are detected in systems with [Zn/Fe] as small as 0.3, the DLA and sub-DLA systems where H2is detected are usually amongst those having the highest metallicities and the largest depletion factors. In particular, H2 is detected in the five systems having the largest depletion factors. Moreover, the individual components where H2is detected have depletion factors systematically larger than other components in the profiles. In two different systems, one of the H2-detected components even has [Zn/Fe]≥1.4. These are the largest depletion factors ever seen in DLA systems. All of this clearly demonstrates the presence of dust in a large fraction of the DLA systems.
The mean H2molecular fraction, f 2N (H2)/[2N (H2) +N (Hi)], is generally small in DLA systems (typically logf < -1) and similar to what is observed in the Magellanic Clouds. There is no correlation between the observed amount of H2and the Hi column density. In fact, two systems where H2is detected have logN (Hi) < 20.3 and, therefore, are sub-DLA systems. From 58 to 75 per cent of the DLA systems have logf < -6. This can be explained if the formation rate of H2on to dust grains is reduced in those systems, probably because the gas is warm (T > 1000 K) and/or the ionizing flux is enhanced relative to what is observed in our Galaxy.
Abstract Copyright: 2003 RAS
Journal keyword(s): galaxies: ISM - quasars: absorption lines - quasars: individual: Q 0347-383 - quasars: individual: Q0405-443 - quasars: individual: Q1444+014 - cosmology: observations
Nomenclature: Tables 2, 3: [LPS2003] QSO J0349-3810 abs N.NNNNN N=5. Tables 4, 5: [LPS2003] QSO J0407-4410 abs N.NNNNN N=5. Tables 6, 7: [LPS2003] QSO J1446+0113 abs N.NNNNN N=5.
CDS comments: Table 8: all the DLAs are already known with an other acronym.
Simbad objects: 27
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