Search for cold gas in strong Mg II absorbers at 0.5  &lt; <i>z</i> &lt;  1.5: nature and evolution of 21-cm absorbers

Gupta, N.; Srianand, R.; Petitjean, P.; Bergeron, J.; Noterdaeme, P.; Muzahid, Sowgat

doi:10.1051/0004-6361/201219159

Cited by 56 publications

(99 citation statements)

References 76 publications

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“…There is tentative evidence for a second absorption component at a frequency of 875.9 MHz, but due to strong RFI we cannot confirm this detection. Note that this system was also observed with the WSRT by Gupta et al (2012), but not detected, although the upper limit on the integral optical depth they quote (τ dV = 0.24 km s −1 ) is lower than the value we measure. The rms noise in our spectrum is approximately 20 per cent lower than what Gupta et al (2012) achieved.…”

Section: B3 0927+469contrasting

confidence: 74%

New H i 21-cm absorbers at low and intermediate redshifts

Liske¹,

Péroux²,

Murphy³

et al. 2015

Mon. Not. R. Astron. Soc.

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We present the results of a survey for intervening H I 21-cm absorbers at intermediate and low redshift (0 < z < 1.2). For our total sample of 24 systems, we obtained high quality data for 17 systems, the other seven being severely affected by radio frequency interference (RFI). Five of our targets are low redshift (z < 0.17) optical galaxies with small impact parameters (< 20 kpc) toward radio-bright background sources. Two of these were detected in 21-cm absorption, showing narrow, high optical depth absorption profiles, the narrowest having a velocity dispersion of only 1.5 km s −1 , which puts an upper limit on the kinetic temperature of T k < 270 K. Combining our observations with results from the literature, we measure a weak anti-correlation between impact parameter and integral optical depth in local (z < 0.5) 21-cm absorbers. Of eleven Ca II and Mg II systems searched, two were detected in 21-cm absorption, and six were affected by RFI to a level that precludes a detection. For these two systems at z ∼ 0.6 we measure spin temperatures of T s = (65 ± 17) K and T s > 180 K. A subset of our systems were also searched for OH absorption, but no detections were made.

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Section: B3 0927+469contrasting

confidence: 74%

New H i 21-cm absorbers at low and intermediate redshifts

Liske¹,

Péroux²,

Murphy³

et al. 2015

Mon. Not. R. Astron. Soc.

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“…Their number per unit redshift is increasing significantly below z abs = 2, probably coupled to an increase in the star-formation efficiency at these redshifts. Gupta et al (2012) report a similarly high detection rate of 21-cm absorbers towards even lower redshifts among strong Mg ii systems, which they argue must be related to the evolution of the CNM filling factor in the latter systems.…”

Section: Discussionmentioning

confidence: 87%

Neutral atomic-carbon quasar absorption-line systems atz> 1.5

Ledoux

Noterdaeme

Petitjean

et al. 2015

A&A

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We present the results of a search for cold gas at high redshift along quasar lines of sight carried out without any a priori assumption on the neutral atomic-hydrogen content of the absorption-line systems. To do this, we systematically looked for neutral-carbon (C i) λλ1560, 1656 transition lines in 41 696 low-resolution quasar spectra (1.5 < z em < 4.46) from the SDSS-II -Data Release 7 -database. C i absorption lines should indeed probe the shielded gas in the neutral interstellar medium of galaxies more efficiently than traditional tracers such as neutral atomic-hydrogen (H i) damped Lyman-α (DLA) and/or Mg ii systems. We built up a sample of 66 C i absorbers with redshifts in the range 1.5 < z < 3.1 and rest-frame equivalent widths 0.1 < W r (λ1560) < 1.7 Å. The completeness limit of our survey is W r,lim (λ1560) 0.4 Å. C i systems stronger than that are more than one hundred times rarer than DLAs at z abs = 2.5. The number of C i systems per unit redshift is found to increase significantly below z = 2. We suggest that these C i absorbers are closely related to the process of star formation and the production of dust in galaxies and that their cosmic evolution is driven by the interplay between dust shielding and the evolution of the ultra-violet background at ∼10 eV. We derive the neutral atomic-hydrogen content of the C i systems observable from the southern hemisphere from VLT/UVES spectroscopy and find that a majority of them are sub-DLAs with N(H i) ∼ 10 20 atoms cm −2 . The dust content of these absorbers is yet significant as seen from the redder optical colours of the corresponding background quasars and their reddened spectral energy distributions, with E(B − V) values up to ∼0.3. The overall N(H i) distribution of C i systems is, however, relatively flat. As a consequence, among the C i systems classifying as DLAs, there is a probable excess of strong DLAs with log N(H i) > 21 (atoms cm −2 ) compared to systematic DLA surveys. Whilst the dust content of such systems is significant, their dust-to-gas ratio must still be limited. Indeed, strong DLAs having large amounts of shielded gas and dust producing stronger reddening and extinction of the background quasars, if they exist, should have been missed in the current magnitude-limited quasar sample. We study the empirical relations between W r (C i), N(H i), E(B − V), and the strength of the 2175 Å extinction feature. The latter is detected in about 30% of the C i absorbers. We show that, at equal amount of reddening, the 2175 Å feature is weak compared to Galactic lines of sight. This is probably the consequence of current or past star formation in the vicinity of the C i systems. We also find that the strongest C i systems tend to have the largest amounts of dust and that the metallicity of the gas and its molecular fraction is likely to be high in a large number of cases. The C i-absorber sample presented here hence provides ideal targets for detailed studies of the dust composition and molecular species at high redshift.

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“…It is expected to contain an imprint of the collective outcome of all the processes that shape the star formation history of the Universe (e.g., Hopkins & Beacom 2006). Systematic searches of high-z intervening 21-cm absorbers in samples of Mg ii systems and damped Lyα systems (DLAs) towards QSOs to measure CNM filling factor of galaxies have resulted in detections of 21-cm absorption towards ∼10-20% of Mg ii systems (e.g., Briggs & Wolfe 1983;Lane 2000;Gupta et al 2009Gupta et al , 2012Kanekar et al 2009), and DLAs (e.g., Kanekar & Chengalur 2003;Curran et al 2010;Srianand et al 2012). However, establishing a connection between the redshift evolution of 21-cm absorbers and global star formation rate (SFR) density is not straight forward due to (i) small number statistics of 21-cm absorbers; (ii) ambiguities regarding the origin of absorbing gas (i.e., gaseous disk, halo or outflowing/infalling gas etc.…”

Section: Introductionmentioning

confidence: 99%

21-cm absorption from galaxies atz~ 0.3

Gupta

Srianand

Noterdaeme

et al. 2013

A&A

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We report the detection of 21-cm absorption from foreground galaxies towards quasars, specifically z gal = 0.3120 towards SDSS J084957.97+510829.0 (z qso = 0.584; Pair-I) and z gal = 0.3714 towards SDSS J144304.53+021419.3 (z qso = 1.82; Pair-II). In both the cases, the integrated 21-cm optical depth is consistent with the absorbing gas being a damped Lyman-α (DLA) system.In the case of Pair-I, strong Na i and Ca ii absorption lines are also detected at z gal in the QSO spectrum. We identify an early-type galaxy at an impact parameter of b ∼ 14 kpc whose photometric redshift is consistent with that of the detected metal and 21-cm absorption lines. This would be the first example of an early-type galaxy associated with an intervening 21-cm absorber. The gas detected in 21-cm and metal absorption lines on the outskirts of this luminous red galaxy could be associated with the reservoir of cold H i gas with a low level of star formation activity in the outer regions of the galaxy as reported in the literature for z ∼ 0.1 earlytype galaxies. In the case of Pair-II, the absorption is associated with a low surface brightness galaxy that, unlike most other known quasar-galaxy pairs (QGPs), i.e. QSO sight lines passing through disks or halos of foreground galaxies, is identified only via narrow optical emission lines detected on top of the QSO spectra. Using SDSS spectra we infer that the emission lines originate within ∼5 kpc of the QSO sight line, and the gas has metallicity [12+O/H] ∼ 8.4 and star formation rate ∼0.7-0.8 M yr −1 . The measured 21-cm optical depth can be reconciled with the N(H i) we derive from the measured extinction (A V = 0.6) if either the H i gas is warm or the extinction per hydrogen atom in this galaxy is much higher than the mean value of the Small Magellanic Cloud. Finally, using a sample of 9 QGPs with 21-cm absorption detection from our observations and literature, we report a weak anti-correlation (Spearman rank, r s = −0.3) between the 21-cm optical depth and galaxy impact parameter. Milliarcsecond scale images and spectra are required to understand the implications of this.

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Search for cold gas in strong Mg II absorbers at 0.5 < z < 1.5: nature and evolution of 21-cm absorbers

Cited by 56 publications

References 76 publications

New H i 21-cm absorbers at low and intermediate redshifts

New H i 21-cm absorbers at low and intermediate redshifts

Neutral atomic-carbon quasar absorption-line systems atz> 1.5

21-cm absorption from galaxies atz~ 0.3

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