MULTI-WAVELENGTH GOALS OBSERVATIONS OF STAR FORMATION AND ACTIVE GALACTIC NUCLEUS ACTIVITY IN THE LUMINOUS INFRARED GALAXY IC 883

摘要

New optical Hubble Space Telescope (HST), Spitzer Space Telescope, Galaxy Evolution Explorer, 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 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 Advanced Camera for Surveys 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 α_(F435W) ~ –2.17 ± 0.22 and α_(F814W) ~ –2.01 ± 0.21, compared with V-band-derived values measured for the well-studied LIRG NGC 34 and the Antennae Galaxy of α ~ –1.7 ± 0.1 and –2.13 ± 0.07, respectively. 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 × 10^(7)-10^(8) yr (for 10^(5) M_☉ clusters), but may be as low as few × 10^(6) yr with extinction factored in. The X-ray and mid-IR spectroscopies are indicative of predominantly starburst-produced nuclear emission, and the star formation rate, estimated based on the assumption that the radio and far-infrared luminosities are tracing the starburst population, is ~80 M_☉ yr^(–1). 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 μIR ~ 2 × 10^(11) L_☉ kpc–2, a factor of 10 less than that of the Orion star-forming region. Finally, the detection of the [Ne V] 14.32 μm emission line is evidence that an active galactic nucleus (AGN) is present. The faintness of the line (i.e., [Ne V]/[Ne II] 12.8 μm ~ 0.01) and the small equivalent width of the 6.2 μm polycyclic aromatic hydrocarbon feature (=0.39 μm) are both indicative of a relatively weak AGN.