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Astron. Astrophys. 343, 367-372 (1999)

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3. The CO distribution and velocity structure

A map of the total integrated [FORMULA] CO line intensity [FORMULA]-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 [FORMULA] 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.

[FIGURE] Fig. 3. The [FORMULA]-distribution of the [FORMULA] CO emission line. The two lowest contour values are 7.7 and 19.2 K km s-1, thereafter the contour interval is 19.2 K km s-1. The equatorial offsets are in units of arcseconds and are measured from the optical nucleus

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 [FORMULA] (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 [FORMULA] CO peak-temperature velocity of 190 km s-1 is found over the [FORMULA] between the two torus maxima. This velocity gradient is close to the corresponding optical velocity gradient of 205 km s-1 over the same [FORMULA] (Sandqvist et al. 1995). It is almost twice that found in the earlier [FORMULA] CO observations, which, however, we simply attribute to the higher resolution of these [FORMULA] CO observations.

[FIGURE] Fig. 4. [FORMULA] [FORMULA] CO position-velocity map along the major axis of NGC 1365; northeast is up and southwest is down. The lowest contour value and the contour interval are 0.15 K

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© European Southern Observatory (ESO) 1999

Online publication: March 1, 1999