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Astron. Astrophys. 325, 124-134

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The interstellar medium in the edge-on galaxy NGC 5907

Cold dust and molecular line emission

M. Dumke1, J. Braine2,3, M. Krause1, R. Zylka1, R. Wielebinski1, and M. Guélin3

1Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany
2Observatoire de Bordeaux, URA 352, CNRS/INSU, B.P. 89, F-33270 Floirac, France
3Institut de Radioastronomie Millimétrique, 300 rue de la Piscine, F-38406 St. Martin d'Hères, France

Received 17 February 1997 / Accepted 18 March 1997


In this paper we present new observations of the interstellar medium in the non-interacting edge-on galaxy NGC 5907. We have observed the J=2-1 and J=1-0 lines of the 12CO molecule and radio continuum emission at 1.2 mm.

The distribution of the molecular gas (as traced by CO) shows a maximum in the central region and a ring or spiral arm at r ~ 7 kpc. Further analysis of the major axis distribution reveals evidence for an inner ring-like structure at r ~ 3.5 kpc. The kinematics can be described by rigid rotation in the inner part, a turnover at ~ 3 kpc, and differential rotation with a velocity of 230 km/s in the outer disk.

The observed continuum emission is mainly due to thermal radiation of cold dust with an average temperature of Td = 18 K, with a small gradient from 20 K to 16 K from the centre to the outer disk. This cold dust component is necessary to explain our results.

The dust emission closely follows the molecular gas in the central region, but is also detected at large radii where no CO can be seen. In these regions the dust absorption cross section per H atom at 1.2mm is estimated to be FORMULA , a value similar to that in the outer parts of other galaxies.

From the FORMULA emission we estimated a molecular mass of NGC 5907 of FORMULA , about FORMULA smaller than from the CO emission. By combining the CO and continuum data we found that the CO-H2-conversion ratio increases with galactocentric radius, from FORMULA at the centre to ~ 1.6 1020 cm-2/K km s-1 at r = 7.5 kpc.

A comparison of NGC 5907 and other edge-on galaxies concerning gas distribution, central kinematics and dust properties is presented.

Key words: galaxies: individual: NGC 5907 - galaxies: ISM - galaxies: kinematics and dynamics - infrared: galaxies - radio continuum: galaxies - radio lines: galaxies

Send offprint requests to: M.D. (mdumke@mpifr-bonn.mpg.de)

© European Southern Observatory (ESO) 1997