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