Molecular Gas and Agn Fueling

CO emission, tracing the molecular content and distribution in galaxies, is a privileged tool to trace gas towards the nucleus, since the HI tracer is in general depleted there. A review is done of recent CO line observations, with sufficient spatial resolution to indicate the morphology and kinematics of the gas near the nucleus. The puzzling result that nuclei presently observed in an active phase have little sign of fueling, is discussed. 1 New high resolution maps Recent surveys of CO molecules in nearby galaxies with millimeter interferometers are coming up: the BIMA SONG survey (Helfer et al. 2003, Sheth et al. 2002), or the NUGA survey (Garćia-Burillo et al. 2003, Combes et al. 2003). The NUGA project consists in mapping at sub-arcsec resolution with the IRAM interferometer more than a dozen of nearby active nuclei, with the goal to reveal the various gas morphologies in the center, and determine the fueling mechanisms. One of the first striking results of these surveys is the wide variety of dynamical perturbations in spiral galaxies, and in particular asymmetries and lopsidedness, in addition to rings, spirals or bars, and embedded structures. NGC 4303 (Sy2) has been mapped in CO at OVRO (Schinnerer et al 2002); it has a large central mass concentration (large bulge), and follows the prototypes of double-bar galaxies. The nuclear bar is encircled by the resonant ring of the primary bar. The bulk of the CO emission comes from two straight gas lanes along the leading sides of the large-scale primary bar. Deviations from circular velocities reach up to 90 km/s, along these gas lanes. There is a conspicuous asymmetry in the center, where the CO gas emission is only weakly correlated to the UV continuum ring. The gas is not in the nuclear bar, nor clearly aligned with the ring (as in the similar types NGC 4314 or NGC 1068) but follows the lanes. From the asymmetry in the CO map, it is obvious that an m=1 self-gravitating mode is superposed to the double-bar structure, and might play a role in the fueling. NGC 5248 (late-type Sy2, Jogee et al. 2002) follows the prototype of a barred galaxy, with low central mass concentration. The spiral structure extends from 10 1 LERMA, Observatoire de Paris, 61 Av. de l’Observatoire, F-75014, Paris, France c © EDP Sciences 2003