next up previous contents
Next: Evolution of the outgassing Up: Scientific results Previous: Structure and kinematics of

The interstellar medium in the edge-on galaxy NGC 5907: Cold dust and molecular line emission

M. Dumke tex2html_wrap_inline1451 , J. Braine tex2html_wrap_inline1623 , M. Krause tex2html_wrap_inline1451 , R. Zylka tex2html_wrap_inline1451 , R. Wielebinski tex2html_wrap_inline1451 , and M. Guélin tex2html_wrap_inline1455
tex2html_wrap_inline1451 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany
tex2html_wrap_inline1453 Observatoire de Bordeaux, URA 352, CNRS/INSU, B.P. 89, F-33270 Floirac, France
tex2html_wrap_inline1455 Institut de Radio Astronomie Millimétrique, 300 Rue de la Piscine, F-38406 Saint Martin d'Hères, France
Abstract: 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 tex2html_wrap_inline1333 molecule and radio continuum emission at tex2html_wrap_inline1645 .

The distribution of the molecular gas (as traced by CO) shows a maximum in the central region and a ring or spiral arm at tex2html_wrap_inline1647 . Further analysis of the major axis distribution reveals evidence for an inner ring-like structure at tex2html_wrap_inline1649 . The kinematics can be described by rigid rotation in the inner part, a turnover at tex2html_wrap_inline1651 , 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 tex2html_wrap_inline1653 , with a small gradient from 20 K to 16 K from the center 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 (Fig. 5). In these regions the dust absorption cross section per H atom at tex2html_wrap_inline1655 is estimated to be tex2html_wrap_inline1657 , a value similar to that in the outer parts of other galaxies.

From the tex2html_wrap_inline1655 emission we estimated a molecular mass of NGC 5907 of tex2html_wrap_inline1661 , about tex2html_wrap_inline1663 smaller than from the CO emission. By combining the CO and continuum data we found that the CO-H tex2html_wrap_inline1303 -conversion ratio increases with galactocentric radius, from tex2html_wrap_inline1667 at the centre to tex2html_wrap_inline1669 at tex2html_wrap_inline1671 .

Accepted for publication in A&A

Figure: Contour map of the continuum emission of NGC 5907 at 245 GHz, overlaid onto an optical image extracted from the Digitized Sky Survey. The beam size of 15'' is indicated by the filled white circle in the lower right corner. The rms noise depends on the location in the map; on the galaxy it is about 1.5 mJy/beam area, contour levels are 4, 8, ..., 24 mJy/beam area

next up previous contents
Next: Evolution of the outgassing Up: Scientific results Previous: Structure and kinematics of