On the absence of molecular absorption in high-redshift millimetre-band searches
Journal article, 2011

We have undertaken a search for millimetre-waveband absorption (through the CO and HCO(+) rotational transitions) in the host galaxies of reddened radio sources (z = 0.405-1.802). Despite the colour selection (optical-near-infrared colours of V - K greater than or similar to 5 in all but one source), no absorption was found in any of the eight quasars for which the background continuum flux was detected. On the basis of the previous (mostly intervening) H(2) and OH detections, the limits reached here and in some previous surveys should be deep enough to detect molecular absorption according to their V - K colours. However, our survey makes the assumption that the reddening is associated with dust close to the emission redshift of the quasar and that the narrow millimetre component of this emission is intercepted by the compact molecular cores. By using the known millimetre absorbers to define the colour depth and comparing this with the ultraviolet luminosities of the sources, we find that, even if these assumptions are valid, only 12 of the 40 objects (mainly from this work) are potentially detectable. This is assuming an excitation temperature of T(x) = 10 K at z = 0, with the number decreasing with increasing temperatures (to zero detectable at T(x) greater than or similar to 100 K).



h i

hydrogen-21 centimeter absorption


quasars: absorption lines


active galactic nuclei


digital sky survey

lyman-alpha systems

cosmology: observations

einstein a-coefficients

galaxies: active

radio lines:

galaxies: high-redshift

galaxies: abundances

oh absorption




S.J. Curran

University of New South Wales (UNSW)

M. T. Whiting

University of New South Wales (UNSW)

Australia Telescope National Facility

F. Combes

LERMA - Laboratoire d'Etudes du Rayonnement et de la Matiere en Astrophysique et Atmospheres

N. Kuno

National Astronomical Observatory of Japan

P. Francis

Australian National University

N. Nakai

University of Tsukuba

J. K. Webb

University of New South Wales (UNSW)

M. T. Murphy

University of New South Wales (UNSW)

Swinburne University of Technology

Tommy Wiklind

Chalmers, Earth and Space Sciences, Onsala Space Observatory

Monthly Notices of the Royal Astronomical Society

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

Vol. 416 3 2143-2153

Subject Categories

Astronomy, Astrophysics and Cosmology



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