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).
vib-rotational
galaxies: high-redshift
lyman-alpha systems
radio lines:
radio-sources
microvariability
galaxies: active
galaxies
galaxies: abundances
quasars: absorption lines
h i
spectrum
active galactic nuclei
cosmology: observations
einstein a-coefficients
optical
hydrogen-21 centimeter absorption
transitions
oh absorption
digital sky survey
Author
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)
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
Swinburne University of Technology
University of New South Wales (UNSW)
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 2143-2153Subject Categories
Astronomy, Astrophysics and Cosmology
DOI
10.1111/j.1365-2966.2011.19193.x