Annu. Rev. Astron. Astrophys. 1991. 29: 581-625 Copyright © 1991 by Annual Reviews. All rights reserved

9.2 NGC 1068

NGC 1068 is the nearest galaxy with both a Seyfert II active nucleus and a high rate of star formation in its inner disk. Half of the total luminosity (2 x 10¹¹ L) originates from an extended disk of young stars at radii < 1.5 kpc (Telesco & Harper 1980); the remainder arises in a source < 0.5" in size, centered on the Seyfert nucleus. This galaxy has been the focus of numerous molecular line studies (see Table 1), with the highest resolution corresponding to 260 pc.

In Figure 14, the integrated CO emission at 2.9" resolution is shown superposed on a U-band optical image (Planesas et al 1991). Two spiral arms of molecular gas are seen encircling the nucleus at a radius of approximately 1.5 kpc, with many distinct emission complexes of size up to 500 pc and masses up to 7 x 10⁸ M. The arms, containing a total H₂ mass of 5 x 10⁹ M, originate at the outer ends of a stellar bar seen in the near infrared (Scoville et al 1988, Thronson et al 1989c). The kinematics of the molecular ring can be fit by circular rotation if the position angle of the major axis is 90° or by rotation plus expansion if the major axis position angle is taken as 40° (Planesas et al 1991).

Figure 14. Map of the integrated CO emission in NGC 1068 overlaid on a U-band image of the inner region of the galaxy (Planesas et al 1991). The major features seen in CO are the inner spiral arms (~ 5 x 109 M) of molecular gas at 15" radius (1.5 kpc), which originate from the ends of the central stellar bar and a compact source (~ 3") coincident with the Seyfert 2 nucleus.

In Figure 14, an emission peak may also be seen coincident with the Seyfert nucleus. Although approximately half of this emission is radio continuum from the central non-thermal source, the remainder is probably CO emission. The total mass of H₂ in the nuclear source at a radii < 130 pc is approximately 8 x 10⁷ M. The dust associated with this gas may be responsible for obscuring the direct line of sight to the Seyfert I nucleus hypothesized on the basis of optical spectropolarimetry (Antonucci & Miller 1985).