Multi-wavelength GOALS Observations of Star Formation and Active Galactic Nucleus Activity in the Luminous Infrared Galaxy IC 883

Abstract

New optical HST, Spitzer, GALEX, and Chandra observations of the single-nucleus, luminous infrared galaxy (LIRG) merger IC 883 are presented. The galaxy is a member of the Great Observatories All-sky LIRG Survey (GOALS), and is of particular interest for a detailed examination of a luminous late-stage merger due to the richness of the optically-visible star clusters and the extended nature of the nuclear X-ray, mid-IR, CO and radio emission. In the HST ACS images, the galaxy is shown to contain 156 optically visible star clusters distributed throughout the nuclear regions and tidal tails of the merger, with a majority of visible clusters residing in an arc ~ 3-7 kpc from the position of the mid-infrared core of the galaxy. The luminosity functions of the clusters have an alpha_F435W ~ -2.17+/-0.22 and alpha_F814W ~ -2.01+/-0.21. Further, the colors and absolute magnitudes of the majority of the clusters are consistent with instantaneous burst population synthesis model ages in the range of a few x10^7 - 10^8 yrs (for 10^5 M_sun clusters), but may be as low as few x10^6 yrs with extinction factored in. The X-ray and mid-IR spectroscopy are indicative of predominantly starburst-produced nuclear emission, and the star formation rate is ~ 80 M_sun / yr. The kinematics of the CO emission and the morphology of both the CO and radio emission are consistent with the nuclear starburst being situated in a highly inclined disk 2 kpc in diameter with an infrared surface brightness mu_IR ~ 2x10^11 L_sun kpc^-2, a factor of 10 less than that of the Orion star-forming region. Finally, the detection of the [Ne V] 14.32 um emission line is evidence that an AGN is present. The faintness of the line (i.e., [Ne V] / [Ne II] um ~ 0.01) and the small equivalent width of the 6.2 um PAH feature ($= 0.39μ$m) are both indicative of a relatively weak AGN. (abridged)