Dynamical Evolution of AGN Host Galaxies - Gas In/Out-Flow Rates in 7 NUGA Galaxies

Authors:
  • SHSebastian Haan
    Sebastian Haan
  • ESEva Schinnerer
    Eva Schinnerer
  • EEEric Emsellem
    Eric Emsellem
  • SGSantiago Garcia-Burillo
    Santiago Garcia-Burillo
  • FCFrancoise Combes
    Francoise Combes
  • CMCarole G. Mundell
    Carole G. Mundell
  • HRHans-Walter Rix
    Hans-Walter Rix
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Abstract
To examine the role of the host galaxy structure in fueling nuclear activity, we estimated gas flow rates from several kpc down to the inner few 10 pc for seven nearby spiral galaxies, selected from the NUGA sample (NUclei of GAlaxies). We calculated gravitational torques from near-IR images and determined gas in/out-flow rates as a function of radius and location within the galactic disks, based on high angular resolution interferometric observations of molecular (CO using PdBI) and atomic (HI using the VLA) gas. The results are compared with kinematic evidence for radial gas flows and the dynamical state of the galaxies (via resonances) derived from several different methods. We show that gravitational torques are very efficient at transporting gas from the outer disk all the way into the galaxies centers at ~100 pc; previously assumed dynamical barriers to gas transport, such as the Corotation Resonance of stellar bars, seem to be overcome by gravitational torque induced gas flows from other non-axisymmmetric structures. The resulting rates of gas mass inflow range from 0.01 to 50 solar masses per year and are larger for the galaxy center than for the outer disk. Our gas flow maps show the action of nested bars within larger bars for 3 galaxies. Non-circular streaming motions found in the kinematic maps are larger in the center than in the outer disk and appear to correlate only loosely with the in/out-flow rates as a function of radius. We demonstrate that spiral gas disks are very dynamic systems that undergo strong radial evolution on timescales of a few rotation periods (e.g. 5 times 10^8 yrs at a radius of 5 kpc), due to the effectiveness of gravitational torques in redistributing the cold galactic gas.