New optical Hubble Space Telescope (HST), Spitzer Space Telescope, and XMM observations of the luminous infrared galaxy (LIRG) NGC 2623 are presented. This galaxy was observed as part of the Great Observatories All-sky LIRG Survey (GOALS). The prominent 3.2 kpc southern extension to the nucleus has been resolved by HST observations into ∼100 star clusters, making it one of the richest off-nuclear concentrations of bright clusters observed in GOALS. The clusters have to Ϫ12.6 mag, which is within the magnitude range of M ∼ Ϫ6.6 F555W Antennae galaxy clusters and in excess of 30 Doradus clusters at the high end. Their optical colors are primarily consistent with ages of ∼1-100 Myr. Archival GALEX data show the off-nuclear region to be extremely bright in the far-ultraviolet, being equivalent in luminosity to the resolved nuclear region at 0.15 mm, but becoming less energetically significant at increasing wavelengths. In addition, [Ne v] 14.3 mm emission is detected with Spitzer IRS, confirming the inference from the X-ray and radio data that an active galactic nucleus (AGN) is present. Thus, the off-nuclear optical clusters are associated with a secondary burst of activity corresponding to a star formation rate ∼0.1-0.2 M yr ; the bulk of infrared (and thus bolometric) luminosity is generated via Ϫ1 , star formation and an AGN embedded behind dust within the inner kiloparsec of the system. If the infrared luminosity is primarily reprocessed starlight, the off-nuclear starburst accounts for !1% of the present star formation in NGC 2623.

We present the results of a Hubble Space Telescope ACS/HRC FUV, ACS/WFC optical study into the cluster populations of a sample of 22 Luminous Infrared Galaxies in the Great Observatories All-Sky LIRG Survey. Through integrated broadband photometry we have derived ages and masses for a total of 484 star clusters contained within these systems. This allows us to examine the properties of star clusters found in the extreme environments of LIRGs relative to lower luminosity star-forming galaxies in the local Universe. We find that by adopting a Bruzual & Charlot simple stellar population (SSP) model and Salpeter initial mass function, the age distribution of clusters declines as dN/dτ = τ −0.9+/−0.3 , consistent with the age distribution derived for the Antennae Galaxies, and interpreted as evidence for rapid cluster disruption occuring in the strong tidal fields of merging galaxies. The large number of 10 6 M young clusters identified in the sample also suggests that LIRGs are capable of producing more high-mass clusters than what is observed to date in any lower luminosity star-forming galaxy in the local Universe. The observed cluster mass distribution of dN/dM = M −1.95+/−0.11 is consistent with the canonical -2 power law used to describe the underlying initial cluster mass function (ICMF) for a wide range of galactic environments. We interpret this as evidence against mass-dependent cluster disruption, which would flatten the observed CMF relative to the underlying ICMF distribution.

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 μ IR ∼ 2 × 10 11 L kpc −2 , a factor of 10 less than that of the Orion star-forming region.