Metallicity and H<scp>i</scp>Column Density Properties of Damped Lyα Systems

Hou, Jing; Shu, C. G.; Shen, Shiyin; Chang, Ruixiang; Chen, W. P.; Fu, Chiyu

doi:10.1086/429358

Cited by 7 publications

(9 citation statements)

References 94 publications

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“…Although a difference can be seen in the range −1.6 < [X/H] < −1, partly due to the bias towards large N(H i), no systematic bias is observed for the UVES sample, apart from any also affecting the Keck sample, as shown by the cumulative distributions (inset). We note that the observed distributions are similar in shape to the distribution derived using simulations by Hou et al (2005, their Fig. 3).…”

Section: Overall Populationsupporting

confidence: 80%

Molecular hydrogen in high-redshift damped Lyman-αsystems: the VLT/UVES database

Noterdaeme

Ledoux

Petitjean³

et al. 2008

A&A

234

355

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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 5 × 10 −7 and f 0.1, where f = 2N(H 2 )/(2N(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 < −5. We find that about 35% of the DLAs with metallicities relative to solar [X/H] ≥ −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] < −1.3 DLAs have log 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(Fe) 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.

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Section: Overall Populationsupporting

confidence: 80%

Molecular hydrogen in high-redshift damped Lyman-αsystems: the VLT/UVES database

Noterdaeme

Ledoux

Petitjean³

et al. 2008

A&A

234

355

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“…Potentially, these could be caused by flat-field errors which become larger at the edges in the PMAS data cubes, but they do satisfy the criteria for being good DLA candidates. The average impact parameter of ∼20 kpc derived for the candidates is larger than expected by numerical simulations, favouring impact parameters of 3 kpc for typical DLA galaxies, with only few DLA galaxies having b > 10 kpc at both high and low redshifts (Okoshi & Nagashima 2005;Hou et al 2005).…”

Section: Impact Parametersmentioning

confidence: 56%

A survey for DLA galaxies with integral field spectroscopy

et al. 2005

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Abstract. Using integral field spectroscopy (IFS) we have observed QSOs which were previously known to have intervening DLAs, to search for emission lines in the field surrounding the QSOs. The sample consists of 13 DLAs plus 7 sub-DLAs at z > 2, from which we find emission line candidates at the expected wavelengths for 8 systems, implying a detection frequency of 40%. Emission lines detected at the DLA redshifts are interpreted as being due to Lyα lines from galaxies associated with the DLA clouds. Candidates are detected at 3 − 4σ levels in both narrow-band images and spectra created from the data cubes. We find no preference for candidate detection associated with either high or low metallicity DLAs. In comparison with the properties of previously known DLA galaxies, the candidates show similar distributions of line fluxes and line widths, but their impact parameters are slightly different, suggesting H i cross sections larger than 10 kpc.

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“…This implies that a typical DLA host galaxy in our model has its SFR 100 times smaller than a typical LBG. Because the number density of DLA host galaxies is about 0.26 (Hou et al 2005) which is about 100 times larger than the observed comoving number density of LBGs, our predictions of cosmic SFR density contributed by DLAs is similar to that of LBGs at z ∼ 3.…”

Section: Cosmic Star Formation Rate Density From Dlas Host Galaxiesmentioning

confidence: 59%

“…Details can be found in Mo et al (1998) and Hou et al (2005). We use Monte Carlo simulation to generate the model DLAs by applying a random sight line passing through the disk.…”

Section: The Modelmentioning

confidence: 99%

Cosmic star formation rate density from DLAs and the HI-metallicity relation

Hou

2005

Proc. IAU

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Abstract. Some basic observational properties of Damped Lymna α systems (DLAs) have been examined by Monte Carlo simulation based on the assumption that DLAs are disks form at the center of dark halo at redshift 3. We found that the predicted cosmic star formation rate density contributed by DLAs is consistent with the most recent observations if the star formation timescale in DLAs is assumed to be 1 ∼ 3 Gyr. By comparing the UV luminosity function between DLA host galaxies and that of Lyman Break Galaxies(LBGs), we show that the DLAs host galaxies are much fainter than LBGs, and that only few percent of DLAs can host LBGs. The discrepancy between model prediction and observation in the correlation between metallicity and HI column density for DLAs is reproduced on the basis of Kennicutt star formation formalism at high redshift. It is quite difficult to interpret this concerning the complexities of dust depletion, star formation mode as well as model limitations. Further investigations are needed.

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Metallicity and HiColumn Density Properties of Damped Lyα Systems

Cited by 7 publications

References 94 publications

Molecular hydrogen in high-redshift damped Lyman-αsystems: the VLT/UVES database

Molecular hydrogen in high-redshift damped Lyman-αsystems: the VLT/UVES database

A survey for DLA galaxies with integral field spectroscopy

Cosmic star formation rate density from DLAs and the HI-metallicity relation

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