3. The CO distribution and velocity structure
A map of the total integrated CO line intensity -distribution is presented in Fig. 3. The interrelation between the emission regions of the CO molecular line, the dust lanes and the H II hot spot regions in the central region of NGC 1365 has already been presented in a conference proceedings (Sandqvist 1996), where the CO contours were superimposed upon a colour index map. In this paper we make a similar comparison - see Fig. 6 - but use instead a Maximum Entropy Method deconvolved map of the CO emission, which we describe in Sect. 4.
There is clear correspondence between the extended CO emission, as represented by the outermost contours, and the dust lanes at the preceding edges of the bar. Even the curved dust feature near the western end of the bar has a corresponding distinctly curved CO component, which can be seen in the lowest contour level. Other dust streamers also contain observable CO.
The most interesting phenomenon, however, is the doubly-peaked CO structure seen near the optical nucleus, with a local minimum right at the nucleus. This structure and its alignment along the major axis of the galaxy is suggestive of a circumnuclear molecular torus with a radius of (450 pc). From the torus, there are CO extensions leading out into the two dominant eastern and western dust lanes.
The overall central CO velocity field was also presented by Sandqvist (1996). Here, we display only the position-velocity map along the major axis of the galaxy in Fig. 4. The velocity gradient across the molecular torus has its maximum value along the major axis and its character in this region may reflect rotation of the torus, which is in the same sense as that of the galaxy itself. A change of CO peak-temperature velocity of 190 km s-1 is found over the between the two torus maxima. This velocity gradient is close to the corresponding optical velocity gradient of 205 km s-1 over the same (Sandqvist et al. 1995). It is almost twice that found in the earlier CO observations, which, however, we simply attribute to the higher resolution of these CO observations.
© European Southern Observatory (ESO) 1999
Online publication: March 1, 1999