Interferometric 12 CO J = 2–1 Image of the Nuclear Region of Seyfert 1 Galaxy NGC 1097

Abstract

We have mapped the central region of the Seyfert 1 galaxy NGC 1097 in 12CO J 2Y1 with the Submillieter Array ( SMA). The 12CO J 2Y1 map shows a central concentration and a surrounding ring coinciding, respectively, with the Seyfert nucleus and a starburst ring. The line intensity peaks at the nucleus, whereas in a previously published 12CO J 1Y0 map the intensity peaks at the starburst ring. The azimuthally averaged 12CO J 1Y0 intensity ratio R21 of the ring is about unity, which is similar to those in nearby active star- forming galaxies, suggesting that most of the molecular gas in the ring is involved in fueling the starburst. The ratio of molecular gas to dynamical mass in the starburst ring shows a somewhat lower value than that found in nearby star- forming galaxies, suggesting that the high R21 of unity may be caused by additional effects, such as shocks induced by gas infall along the bar. The molecular gas can last for about 1: 2; 108 yr without further replenishment, assuming a constant star formation rate. The central gas is rotating with the molecular ring in the same direction, while its velocity gradient is steeper than that of the ring, and similar to what usually observed in Seyfert 2 galaxies. To view the Seyfert nucleus without obscuration, the central gas can be a low- inclined disk or torus but not too low to be less massive than the mass of the host galaxy, or be a highly inclined thin disk or clumpy and thick torus, inner part of the galactic disk is also possible. The R21 of similar to 1.9 of the central gas is significantly higher than that of the ring, indicates that the activity of the Seyfert nucleus may significant influence the central gas.