A submillimeter exponential disk in M 51: Evidence for an extended cold dust disk

Free access article

Issue		A&A Volume 430, Number 2, February I 2005


Page(s)		427 - 434
Section		Extragalactic astronomy
DOI		http://dx.doi.org/10.1051/0004-6361:20040469

A&A 430, 427-434 (2005)
DOI: 10.1051/0004-6361:20040469

A submillimeter exponential disk in M 51: Evidence for an extended cold dust disk

R. Meijerink¹, R. P. J. Tilanus², C. P. Dullemond³, F. P. Israel¹ and P. P. van der Werf¹

¹ Sterrewacht Leiden, PO Box 9513, 2300 RA Leiden, The Netherlands
e-mail: meijerin@strw.leidenuniv.nl
² Joint Astronomy Centre, 660 N. A'ohoku Pl., Hilo, Hawaii, 96720, USA
³ Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, Postfach 13 17, 85741 Garching, Germany

(Received 18 March 2004 / Accepted 21 September 2004 )

Abstract
A 850 $\mu$ m map of the interacting spiral galaxy M 51 shows well-defined spiral arms, closely resembling the structures seen in CO and HI emission. However, most of the 850 $\mu$ m emission originates in an underlying exponential disk, a component that has not been observed before in a face-on galaxy at these wavelengths. The scale-length of this disk is 5.45 kpc, which is somewhat larger than the scale-length of the stellar disk, but somewhat smaller than that of atomic hydrogen. Its profile cannot be explained solely by a radial disk temperature gradient but requires the underlying dust to have an exponential distribution as well. This reinforces the view that the submm emission from spiral galaxy disks traces total hydrogen column density, i.e. the sum of H ₂and H I. A canonical gas-to-dust ratio of $100\pm26$ is obtained for $\kappa_{850}=1.2$ g ^-1 cm ², where $\kappa_{850}$ is the dust opacity at 850 $\mu$ m.

Key words: Galaxy: general -- galaxies: ISM -- radio continuum: galaxies

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