Detecting Cold Gas at Intermediate Redshifts: Giant Metrewave Radio Telescope Survey Using Mg
                    <scp>ii</scp>
                    Systems

Gupta, N.; Srianand, R.; Petitjean, P.; Khare, Pushpa; Saikia, D. J.; York, Donald G.

doi:10.1086/511153

Cited by 28 publications

(46 citation statements)

References 23 publications

(23 reference statements)

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“… References: K06 –Kanekar et al (2006); G07 –Gupta et al (2007); K07 –Kanekar et al (2007); C07 – This paper. …”

Section: Observations and Resultsmentioning

confidence: 99%

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Relationships between the H i 21-cm line strength, Mg ii equivalent width and metallicity in damped Lyman α absorption systems

Curran¹,

Tzanavaris²,

Pihlström³

et al. 2007

Monthly Notices of the Royal Astronomical Society

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We present the results of a survey for 21‐cm absorption in four never previously searched damped Lyman α absorption systems (DLAs) with the Westerbork Synthesis Radio Telescope. The one detection is presented and discussed in Curran et al. and here we add our results to other recent studies in order to address the important issues regarding the detection of cold gas, through 21‐cm absorption, in DLAs. Although, due to the DLAs identified with spiral galaxies, there is a mix of spin temperature/covering factor ratios at low redshift, two recent high redshift end points confirm that this ratio does not generally rise much above Tspin/f∼ 103 K over the whole redshift range searched (up to zabs= 3.39). That is, if the covering factors of many of these galaxies were a factor of ≥2 smaller than for the spirals (which span 120 ≤Tspin/f≤ 520 K), then no significant difference in the spin temperatures between these two classes would be required. Furthermore, although it is difficult to separate the relative contributions of the spin temperature and covering factor, the new results confirm that 21‐cm detections tend to occur at low angular diameter distances, where the coverage of a given absorption cross‐section is maximized. This indicates a dominant contribution by the covering factor. Indeed, the two new high redshift detections occur towards two extremely compact radio sources (≤0.04 arcsec), although the one other new detection, which may have an impact parameter in excess of 75 kpc, occurs towards one of the largest radio sources. Finally, we also find an apparent 21‐cm line strength–Mg ii equivalent width correlation, which appears to be due to a coupling of the velocity structure between the components that each species traces. That is, the gas seen in 21‐cm absorption could be the same as that seen in optical absorption. Combined with the known equivalent width–metallicity relation, this may be manifest as a spin temperature–metallicity anticorrelation, which is non‐evolutionary in origin.

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“… References: K06 –Kanekar et al (2006); G07 –Gupta et al (2007); K07 –Kanekar et al (2007); C07 – This paper. …”

Section: Observations and Resultsmentioning

confidence: 99%

“… b DLA candidates only and so neutral hydrogen column densities are unavailable, hence the upper limits in N H I for the non‐detections. Note that the sub‐DLA 0237−223 is common to both Gupta et al (2007) and Srianand et al (2007). …”

Section: Discussionmentioning

confidence: 99%

Relationships between the H i 21-cm line strength, Mg ii equivalent width and metallicity in damped Lyman α absorption systems

Curran¹,

Tzanavaris²,

Pihlström³

et al. 2007

Monthly Notices of the Royal Astronomical Society

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“…The H i 21‐cm absorption towards this absorber has a narrow profile that is well fitted with a simple two‐Gaussian model (Gupta et al 2007; Kanekar et al 2009b). As noted in , there is evidence of a core–jet structure in the 606 MHz VLBA image, which leads to a core covering factor of 0.32.…”

Section: Observationsmentioning

confidence: 87%

H i content, metallicities and spin temperatures of damped and sub-damped Lyα systems in the redshift desert (0.6 < zabs < 1.7)★

Ellison¹,

Kanekar²,

Prochaska³

et al. 2012

Monthly Notices of the Royal Astronomical Society

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The H i 21‐cm absorption optical depth and the N(H i) column density derived from Lyα absorption can be combined to yield the spin temperature (Ts) of intervening damped Lyα systems (DLAs). Although spin temperatures have been determined for samples of DLAs with zabs < 0.6 and zabs > 1.7, the intermediate regime currently contains only two Ts measurements, leading to a ‘redshift desert’ that spans 4 Gyr of cosmic time. To connect the low‐ and high‐redshift regimes, we present observations of the Lyα line of six 0.6 < zabs < 1.7 H i 21‐cm absorbers. The data set is complemented by both low‐frequency Very Long Baseline Array observations (to derive the absorber covering factor, f) and optical echelle spectra from which metal abundances are determined. Our data set therefore not only offers the largest statistical study of H i 21‐cm absorbers to date, and bridges the redshift desert, but is also the first to use a fully f‐corrected data set to look for metallicity‐based trends. The metallicities of H i 21‐cm absorbers are consistent with those of optically selected DLAs at the same redshift. In agreement with trends found in Galactic sightlines, we find that the lowest column density absorbers tend to be dominated by warm gas. In the DLA regime, spin temperatures show a wider range of values than Galactic data, as may be expected in a heterogeneous galactic population. However, we find that low‐metallicity DLAs are dominated by small cold gas fractions and only absorbers with relatively high metallicities exhibit significant fractions of cold gas. Using a compilation of H i 21‐cm absorbers which are selected to have covering‐factor‐corrected spin temperatures, we confirm an anticorrelation between metallicity and Ts at 3.4σ significance. Finally, one of the DLAs in our sample is a newly discovered H i 21‐cm absorber (at zabs= 0.602 towards J1431+3952), which we find to have the lowest f‐corrected spin temperature yet reported in the literature: K. The observed distribution of Ts and metallicities in DLAs and the implications for understanding the characteristics of the interstellar medium in high‐redshift galaxies are discussed.

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“…Gupta et al () have reported 21‐cm absorption from the z abs = 1.371 Mg ii system towards J0108−0037. Despite a low rest equivalent width of ∼0.3 Å for the Mg ii doublet, other absorption lines of weaker metal transitions are clearly seen even in the Sloan Digital Sky Survey (SDSS) spectrum.…”

Section: Gaussian Fits To 21‐cm Absorption Linesmentioning

confidence: 99%

Constraining the variation of fundamental constants at z ∼ 1.3 using 21-cm absorbers

Rahmani

Srianand

Gupta

et al. 2012

Monthly Notices of the Royal Astronomical Society

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We present high‐resolution optical spectra obtained with the Ultraviolet and Visual Echelle Spectrograph at the Very Large Telescope and 21‐cm absorption spectra obtained with the Giant Metrewave Radio Telescope and the Green Bank Telescope of five quasars along the line of sight of which 21‐cm absorption systems at 1.17 < z < 1.56 have been detected previously. We also present milliarcsecond‐scale radio images of these quasars obtained with the Very Large Baseline Array. We use the data on four of these systems to constrain the time variation of x ≡ gpα2/μ, where gp is the proton gyromagnetic factor, α is the fine structure constant and μ is the proton‐to‐electron mass ratio. We carefully evaluate the systematic uncertainties in redshift measurements using cross‐correlation analysis and repeated Voigt profile fitting. In both cases, we also confirm our results by analysing optical spectra obtained with the Keck telescope. We find the weighted and the simple means of Δx/x to be, respectively, −(0.1 ± 1.3) × 10−6 and (0.0 ± 1.5) × 10−6 at the mean redshift of 〈z〉 = 1.36 corresponding to a look‐back time of ∼9 Gyr. This is the most stringent constraint ever obtained on Δx/x. If we only use the two systems towards quasars unresolved at milliarcsecond scales, we get the simple mean of Δx/x = +(0.2 ± 1.6) × 10−6. Assuming the constancy of other constants, we get Δα/α = (0.0 ± 0.8) × 10−6, which is a factor of 2 better than the best constraints obtained so far using the many‐multiplet method. On the other hand, assuming that α and gp have not varied we derive Δμ/μ = (0.0 ± 1.5) × 10−6 which is again the best limit ever obtained on the variation of μ over this redshift range. Using independent constraints on Δα/α at z < 1.8 and Δμ/μ at z ∼ 0.7 available in the literature, we get Δgp/gp ≤ 3.5 × 10−6(1σ).

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Detecting Cold Gas at Intermediate Redshifts: Giant Metrewave Radio Telescope Survey Using Mg ii Systems

Cited by 28 publications

References 23 publications

Relationships between the H i 21-cm line strength, Mg ii equivalent width and metallicity in damped Lyman α absorption systems

Relationships between the H i 21-cm line strength, Mg ii equivalent width and metallicity in damped Lyman α absorption systems

H i content, metallicities and spin temperatures of damped and sub-damped Lyα systems in the redshift desert (0.6 < zabs < 1.7)★

Constraining the variation of fundamental constants at z ∼ 1.3 using 21-cm absorbers

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