H i 21 cm absorption at z ∼ 2.347 towards PKS B0438-436

Abstract

We report the detection of redshifted H i 21‐cm absorption in the z∼ 2.347 damped Lyman α absorber (DLA) towards PKS B0438−436 with the Green Bank Telescope. This is the second‐highest redshift at which 21‐cm absorption has been detected in a DLA. The absorption extends over ∼60 km s−1 and has two distinct components, at z= 2.347 477(12) and z= 2.347 869(20). A similar velocity structure is seen in optical metal lines, although the peak absorption here is offset by ∼11 km s−1 from the peak in the 21‐cm line. We obtain a high spin temperature Ts∼ (886 ± 248) × (f/0.58) K, using a covering factor estimated from 2.3‐GHz very long baseline interferometry data. However, the current data cannot rule out a low spin temperature. The non‐detection of CO 3–2 absorption places the upper limit NCO < 3.8 × 1015 (Tx/10) cm−2 on the CO column density.

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

“…This may mean that the strongest 21 cm absorption component is not associated with the strongest metal absorption component. Such shifts have already been observed in other systems (see Srianand et al 2005;Kanekar et al 2006;Heinmüller et al 2006). It is also known that H 2 carrying components in DLAs, that are believed to trace the CNM gas, often show similar shifts (although less pronounced) with respect to the strong metal-line components (Ledoux et al 2003).…”

“…Motivated by this, we have begun a GMRT 21 cm survey of DLA candidates selected on the basis of W(Mg ii) in the redshift range . Our complete sample is drawn from the 1.10 ≤ z ≤ 1.45 catalog of 7421 Mg ii systems with and W(Mg ii) ≥ 1 A , detected along the line of sight toward 45,023 0.3 ≤ z ≤ 1.9 QSOs in the Sloan Digital Sky Survey (SDSS) Data Release 3 (Table 1 of Curran et al 2005 and toward PKS 0438Ϫ436 from Kanekar et al 2006). Shaded histoz p 2.347 gram is for the confirmed 21 cm absorption systems.…”

Keck telescope constraint on cosmological variation of the proton-to-electron mass ratio

“…A variety of analyses using different metal ions have been performed (e.g. Wolfe, Brown & Roberts 1976; Tzanavaris et al 2005; Kanekar et al 2006), with measurements from nine absorption systems at 0.23 < z abs < 2.35 by Tzanavaris et al (2007) providing a constraint of Δ X / X = (+6.3 ± 9.9) × 10 −6 . However, the fact that the H i 21‐cm and metal‐line velocity structures are observationally dissimilar – probably because the radio morphology of most background quasars is not point like – means that improvements must come by averaging over many sightlines and/or carefully selecting quasars with point‐like radio morphologies.…”

Directly imaging damped Ly α galaxies at z > 2 – III. The star formation rates of neutral gas reservoirs at z ∼ 2.7

“…Similarly, the paucity of cold gas and molecules in high-redshift DLAs (see e.g. Carilli et al 1996;Curran & Webb 2006;Jorgenson et al 2006Kanekar et al 2006Kanekar et al , 2014Noterdaeme et al 2008;Ellison et al 2012;Srianand et al 2012) points towards an environment that is atypical for dusty, gas rich, galaxies. Finally, we note that, although the exact relationship between the observed cooling rate and the UV photon flux may be subject of future revision, the presence of high-cool DLAs disfavour a scenarios in which the UV radiation field is completely suppressed by dust.…”