Open AccessH i 21 cm absorption at z ∼ 2.347 towards PKS B0438–436
Author(s) -
Kanekar N.,
Subrahmanyan R.,
Ellison S. L.,
Lane W. M.,
Chengalur J. N.
Publication year - 2006
Publication title -
monthly notices of the royal astronomical society: letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.067
H-Index - 122
eISSN - 1745-3933
pISSN - 1745-3925
DOI - 10.1111/j.1745-3933.2006.00186.x
Subject(s) - physics , redshift , astrophysics , green bank telescope , absorption (acoustics) , absorption spectroscopy , analytical chemistry (journal) , offset (computer science) , interferometry , optics , galaxy , chromatography , chemistry , computer science , programming language
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 T s ∼ (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 N CO < 3.8 × 10 15 ( T x /10) cm −2 on the CO column density.