Global molecular gas properties of Seyfert galaxies

Free access article

Issue		A&A Volume 373, Number 2, July II 2001


Page(s)		459 - 472
Section		Extragalactic astronomy
DOI		http://dx.doi.org/10.1051/0004-6361:20010635

A&A 373, 459-472 (2001)
DOI: 10.1051/0004-6361:20010635

II. Analysis of the results

S. J. Curran^{1, 2, 3}, A. G. Polatidis¹, S. Aalto¹ and R. S. Booth¹

¹ Onsala Space Observatory, Chalmers University of Technology, 439 92 Onsala, Sweden
² European Southern Observatory, Casilla 19001, Santiago 19, Chile
³ School of Physics, University of New South Wales, Sydney NSW 2052, Australia

(Received 3 April 2001 / Accepted 24 April 2001 )

Abstract
We use the data published in Paper I and Curran et al. (2000) to determine the global molecular gas luminosities and distributions in a sample of 22 Seyfert galaxies. From this we find definite differences in the CO to HCN luminosity ratios between the near-by and distant galaxies of the sample. This is perhaps due to a selection effect where we only observe the brightest of the distant sources. With regard to distributions, we find in the near-by (mapped) sample that the CO is usually much wider distributed than the central telescope beam and that the HCN is considerably more extended beyond the ~1 kpc often cited in the literature. In fact this molecule has been detected as far as $\approx$ 5 kpc from the centre of NGC 1365. We may also have detected a bar in HCN in NGC 5033. Also, using the data to complement the results of Curran (2000a), $\frac{L_{\rm CO}}{L_{\rm FIR}}({\rm Sy2})\approx\frac{L_{\rm CO}}{L_{\rm FIR}}({\rm Sy1})$ i.e. no difference in the molecular gas luminosities between the two main Seyfert classes. In fact we consider it more meaningful to discuss the differences between the near-by and distant sample (irrespective of Seyfert type), although both of these samples may show evidence that much of the far infrared luminosity could arise from an active galactic nucleus as opposed to being predominantly due to vigorous star formation. We do believe, however, that improved statistics would be of little value in distinguishing between these two scenarios and that future high resolution observations are the key to resolving this issue.

Key words: galaxies: Seyfert -- galaxies: starburst -- galaxies: abundances -- galaxies: ISM

Offprint request: S. Curran, sjc@bat.phys.unsw.edu.au

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