A Gas‐rich Nuclear Bar Fueling a Powerful Central Starburst in NGC 2782

Abstract

We present evidence that the peculiar interacting starburst galaxy NGC 2782 (Arp 215) harbors a gas-rich nuclear stellar bar feeding an M82-class powerful central starburst, from a study based on high-resolution interferometric CO (J = 1 → 0) data and optical BVR and Hα observations, along with available near-infrared (NIR) images, a 5 GHz radio continuum map, and archival Hubble Space Telescope (HST) images. Morphological and kinematic data show that NGC 2782 harbors a clumpy, barlike CO feature of radius ~75 (1.3 kpc) that leads a nuclear stellar bar of similar size. The nuclear barlike CO feature is massive: it contains ~2.5 × 109 M☉ of molecular gas, which makes up ~8% of the dynamical mass present within a 1.3 kpc radius. Within the CO bar, emission peaks in two extended clumpy lobes that lie on opposite sides of the nucleus, separated by ~6'' (1 kpc). Between the CO lobes, in the inner 200 pc radius, resides a powerful central starburst that is forming stars at a rate of 3-6 M☉ yr-1. While circular motions dominate the CO velocity field, the CO lobes show weak barlike streaming motions on the leading side of the nuclear stellar bar, suggestive of gas inflow. We estimate semianalytically the gravitational torque from the nuclear stellar bar on the gas and suggest large gas inflow rates from the CO lobes into the central starburst. These observations, which are among the first ones showing a nuclear stellar bar fueling molecular gas into an intense central starburst, are consistent with simulations and theory, which suggest that nuclear bars provide an efficient way of transporting gas closer to the galactic center to fuel central activity. Furthermore, several massive (107-108 M☉) clumps are present at low radii, and dynamical friction might produce further gas inflow. We suggest that the nuclear barlike molecular gas feature and central activity will be very short lived, likely disappearing within 5 × 108 yr.