Molecular hydrogen in high-redshift Damped Lyman-alpha systems: The VLT/UVES database

By P. Noterdaeme, C. Ledoux, P. Petitjean, R. Srianand. 2008

180 citations recorded by the source corpus.

Aims. We present the current status of ongoing searches for molecular hydrogen in high-redshift (1.8 z abs ≤ 4.2) Damped Lyman- α systems (DLAs) capitalising on observations performed with the ESO Very Large Telescope (VLT) Ultraviolet and Visual Echelle Spectrograph (UVES). Methods. We identify 77 DLAs/strong sub-DLAs, with log N (H I) ≥ 20 and z abs >1.8, which have data that include redshifted H 2 Lyman and/or Werner-band absorption lines. This sample of H I, H 2 and metal line measurements, performed in an homogeneous manner, is more than twice as large as our previous sample (Ledoux et al. 2003) considering every system in which searches for H 2 could be completed so far, including all non-detections. Results. H 2 is detected in thirteen of the systems, which have molecular fractions of values between f $\simeq$ 5$\times$10 -7 and f $\simeq$ 0.1, where f = 2 N (H 2 )/(2 N (H 2 )+N(H I)). Upper limits are measured for the remaining 64 systems with detection limits of typically log N (H 2 )~14.3, corresponding to log f ≥ -1.3 (i.e., 1/20th solar), with X = Zn, S or Si, have molecular fractions log f > -4.5, while H 2 is detected – regardless of the molecular fraction – in ∼ 50% of them. In contrast, only about 4% of the [X/H] f > -4.5. We show that the presence of H 2 does not strongly depend on the total neutral hydrogen column density, although the probability of finding log f > -4.5 is higher for log N (H I) ≥ 20.8 than below this limit (19% and 7% respectively). The overall H 2 detection rate in log N (H I) ≥ 20 DLAs is found to be about 16% (10% considering only log f > -4.5 detections) after correction for a slight bias towards large N (H I). There is a strong preference for H 2 -bearing DLAs to have significant depletion factors, [X/Fe] > 0.4. In addition, all H 2 -bearing DLAs have column densities of iron into dust grains larger than log $N({\rm Fe})_{\rm dust}$~ 14.7, and about 40% of the DLAs above this limit have detected H 2 lines with log f > -4.5. This demonstrates the importance of dust in governing the detectability of H 2 in DLAs. Our extended sample supports neither the redshift evolution of the detection fraction of H 2 -bearing DLAs nor that of the molecular fraction in systems with H 2 detections over the redshift range 1.8 z abs ≤ 3.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/ff825b8d5b380b296a73d06f34491f63709ed1d3

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In Astronomy and Astrophysics

1. C. Baugh
2. A. Benson
3. R. Dav'e
4. M. Pettini
5. C. Steidel
6. R. Somerville
7. P. Hopkins
8. C. Lacey

In Instrumentation

1. A. Benson
2. C. Baugh
3. C. Steidel
4. M. Pettini
5. C. Lacey
6. G. Rudie
7. A. Shapley
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Citations in the corpus

• Evolution of the cosmological mass density of neutral gas from Sloan Digital Sky Survey II - Data Release 7 (2009, background): “In addition, there is only a small tendency for increasing H2 molecular fraction with larger Hi column density (Ledoux et al. 2003; Noterdaeme et al. 2008a).”
• First detection of CO in a high-redshift damped Lyman-α system (2008, background): “13 H2 absorption systems at 1.8 < z < 4.3 out of a total of 77 DLAs (Ledoux et al. 2003, 2006; Petitjean et al. 2006; Noterdaeme et al. 2008).”
• The most metal-poor damped Lyα systems: insights into chemical evolution in the very metal-poor regime★ (2011, background): “In fact, since the physical conditions of the gas that gives rise to DLAs are conducive to forming stars (Noterdaeme et al. 2008; Jorgenson et al. 2009), it certainly seems plausible that some of the VMP stars in the halo of our Galaxy originally condensed out of a VMP DLA.”
• Cosmic evolution of the atomic and molecular gas contents of galaxies (2011, background): “However, a few detections of H2 absorption in the lines-of-sight to QSOs have been reported (e.g. Noterdaeme et al. 2008; Tumlinson et al. 2010; Srianand et al. 2010), as well asCO detections in a large number of luminous star-forming galaxies (e.g. Greve et al. 2005; Geach et al. 2009; Daddi et…”