, M. Guélin
, M. Dumke
,
N. Brouillet
, F. Herpin
, R. Wielebinski
IRAM (Grenoble)
MPIfR, Auf dem Hügel 69, D-53121 Bonn
Obs de Bordeaux, 2 rue de l'Observatoire, F-33270 Floirac 
continuum map of the (mostly) thermal dust
emission from the edge-on spiral NGC 3079 taken with the 19-channel
MPIfR bolometer mounted on the IRAM 30meter telescope. At about 
(
) North of the center, a strong secondary maximum is
detected at 
corresponding to an HI and radio continuum
peak. The CO lines were detected here but very weak. This is a
clear detection of the dust associated with the atomic gas
component in an external galaxy.
The CO(1--0) and CO(2--1) lines were observed and detected out to a
radius of 
for an assumed distance of 
. The line
width of the nuclear spectrum exceeds the global line width (
i.e. as determined by the rotation curve at 
) by over
. No evidence for a compact nuclear source is seen in any
of these maps (roughly 
resolution).
Assuming that the 
dust emission can be decomposed into
emission from dust in the atomic and in the molecular interstellar
medium, we derive the emissivity of the dust associated with the
relatively diffuse atomic gas. Based on this value, and taking the
emissivities for the diffuse atomic gas as lower limits
(cf. Hildebrandt 1983), we estimate 
conversion factors of
in the disk and 
in the nucleus, far below
standard estimates. The star formation efficiency must be very high
in the central region.
An interesting feature of our data is the variation of the CO(2--1)
line to continuum ratio, from 
40% in the nuclear region
decreasing by a factor 10 with radius (see Fig. 1). We
interpret this as being largely due to a decrease in the gas
temperature and suggest that the CO(2--1) line to continuum ratio may
be a useful thermometer for studies of the ISM in galaxies.
Figure 1: CO(2--1) line to continuum ratio as a function of radial distance
in NGC 3079