COLD DUST AND MOLECULAR LINE EMISSION IN NGC-4565

Using the IRAM 30-m telescope, we have mapped the lambda 1.2 mm contin uum emission and the (CO)-C-12 J= 1-->0 and 2-->1 line emissions in th e edge-on spiral galaxy NGC 4565. We selected NGC 4565 because it is s trong in the HI line, but weak in CO, contrary to the galaxies mapped so far at 1.2 mm. The CO emission in NGC 4565 resembles that in the Mi lky Way. It shows a compact central source surrounded by a 'molecular ring'. The molecular ring peaks between 1' and 1.5' from the center (3 - 5 kpc) and has an outer radius of similar or equal to 3'. It is twi ce smaller than the broad 'plateau' observed in HI and shows narrow st ructures which could be spiral arms. The lambda 1.2 mm continuum follo ws CO near the center and HI at the periphery. It shows, like CO, a ce ntral peak and an inner ring and, like HI, a weaker, extended plateau. This is the first time that dust emission is unambiguously detected i n extragalactic HI clouds. Like HI, the 1.2 mm contours are warped nea r the NW edge of the galaxy. The warp, already apparent at half the op tical radius, reaches a height of 50 '' (2.4 kpc) at the edge of the o ptical disk. The average dust temperature is 18 K near the center and 15 K in the HI plateau. From the 1.2 mm continuum intensity and the HI line integrated intensity, we derive a dust absorption cross section per H atom sigma(1.2mm)(H) = tau/N-H = 5 X 10(-27) cm(2) in the platea u. This value is very close to that predicted by Draine & Lee (1984) f or the local diffuse clouds. The velocity field derived from CO can be described by rotation (solid body rotation between 0 and 4 kpc, const ant velocity further out) plus non-circular motions. The non-circular motions are observed mostly near the 'arms' and near the nucleus. They are probably the signature of a spiral density wave and/or of a centr al bar. The presence of a bar could explain the boxy shape of the cent ral bulge on optical photographs.