Redshifted H I and OH absorption in radio galaxies and quasars
Journal article, 2011

From a survey for the redshifted H i 21-cm and OH 18-cm absorption in the hosts of a sample of radio galaxies and quasars, we detect H i in three of the 10 and OH in none of the 14 sources for which useful data were obtained. As expected from our recent result, all of the 21-cm detections occur in sources with ultraviolet (UV) continuum luminosities of L(UV) < 1023 W Hz-1. At these 'moderate' luminosities, we also obtain four non-detections, although, as confirmed by the equipartition of detections between the type 1 and type 2 objects, this near-50 per cent detection rate cannot be attributed to unified schemes of active galactic nuclei (AGNs). All of our detections are at redshifts of z less than or similar to 0.67, which, in conjunction with our faint source selection, biases against UV luminous objects. The importance of the UV luminosity (over AGN type) in the detection of the 21-cm absorption is further supported by the non-detections in the two high-redshift (z similar to 3.6-3.8) radio galaxies, which are both type 2 objects, while having L(UV) > 1023 W Hz-1. Our 21-cm detections in combination with those previously published give a total of eight (associated and intervening) H i-absorbing sources searched and undetected in OH. Using the detected 21-cm line strengths to normalize the limits, we find that only two of these eight sources may have been searched sufficiently deeply in OH, even though these are marginal.

sky survey

ultraviolet: galaxies

fundamental constants

unified schemes

galaxies: fundamental parameters




active galactic nuclei

red quasars


absorbing gas

21 cm absorption

galaxies: active

quasars: absorption lines

radio lines: galaxies

flat-spectrum sample



S.J. Curran

University of New South Wales (UNSW)

M. T. Whiting

University of New South Wales (UNSW)

Commonwealth Scientific and Industrial Research Organisation (CSIRO)

M. T. Murphy

University of Cambridge

Swinburne University of Technology

J. K. Webb

University of New South Wales (UNSW)

C. Bignell

National Radio Astronomy Observatory

A. G. Polatidis

Netherlands Institute for Radio Astronomy (ASTRON)

Max Planck Society

Tommy Wiklind

Chalmers, Earth and Space Sciences, Onsala Space Observatory

P. Francis

Australian National University

G. Langston

National Radio Astronomy Observatory

Monthly Notices of the Royal Astronomical Society

0035-8711 (ISSN) 1365-2966 (eISSN)

Vol. 413 2 1165-1173

Subject Categories

Astronomy, Astrophysics and Cosmology



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