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On the absence of molecular absorption in high-redshift millimetre-band searches

S. J. Curran ; M. T. Whiting ; F. Combes ; N. Kuno ; P. Francis ; N. Nakai ; J. K. Webb ; M. T. Murphy ; Tommy Wiklind (Institutionen för rymd- och geovetenskap, Onsala rymdobservatorium)
Monthly Notices of the Royal Astronomical Society (0035-8711). Vol. 416 (2011), 3, p. 2143-2153.
[Artikel, refereegranskad vetenskaplig]

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).

Nyckelord: galaxies: abundances, galaxies: active, galaxies: high-redshift, quasars: absorption lines, cosmology: observations, radio lines:, galaxies, digital sky survey, hydrogen-21 centimeter absorption, vib-rotational, transitions, einstein a-coefficients, active galactic nuclei, spectrum, radio-sources, lyman-alpha systems, oh absorption, h i, optical, microvariability

Denna post skapades 2011-11-03.
CPL Pubid: 148106


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Institutioner (Chalmers)

Institutionen för rymd- och geovetenskap, Onsala rymdobservatorium (2010-2017)


Astronomi, astrofysik och kosmologi

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