STELLAR AND MOLECULAR GAS KINEMATICS OF NGC 1097: INFLOW DRIVEN BY A NUCLEAR SPIRAL

Abstract

We present spatially resolved distributions and kinematics of the stars and\nmolecular gas in the central 320pc of NGC1097. The stellar continuum confirms\nthe previously reported 3-arm spiral pattern extending into the central 100pc.\nThe stellar kinematics and the gas distribution imply this is a shadowing\neffect due to extinction by gas and dust in the molecular spiral arms. The\nmolecular gas kinematics show a strong residual (i.e. non-circular) velocity,\nwhich is manifested as a 2-arm kinematic spiral. Linear models indicate that\nthis is the line-of-sight velocity pattern expected for a density wave in gas\nthat generates a 3-arm spiral morphology. We estimate the inflow rate along the\narms. Using hydrodynamical models of nuclear spirals, we show that when\nderiving the accretion rate into the central region, outflow in the disk plane\nbetween the arms has to be taken into account. For NGC1097, despite the inflow\nrate along the arms being ~1.2Msun/yr, the net gas accretion rate to the\ncentral few tens of parsecs is much smaller. The numerical models indicate that\nthe inflow rate could be as little as ~0.06Msun/yr. This is sufficient to\ngenerate recurring starbursts, similar in scale to that observed, every\n20-150Myr. The nuclear spiral represents a mechanism that can feed gas into the\ncentral parsecs of the galaxy, with the gas flow sustainable for timescales of\na Gigayear.\n