[en] 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 × 10⁷-10⁸ yr (for 10⁵ M_☉ clusters), but may be as low as few × 10⁶ 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 × 10¹¹ 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.

[en] We present results of Hubble Space Telescope (HST) NICMOS H-band imaging of 73 of the most luminous (i.e., log[L_IR/L_sun]>11.4) infrared galaxies (LIRGs) in the Great Observatories All-sky LIRG Survey. This data set combines multi-wavelength imaging and spectroscopic data from space-based (Spitzer, HST, GALEX, and Chandra) and ground-based telescopes. In this paper, we use high-resolution near-infrared data to recover nuclear structure that is obscured by dust at optical wavelengths and measure the evolution in this structure along the merger sequence. A large fraction of all galaxies in our sample possess double nuclei (∼63%) or show evidence for triple nuclei (∼6%). Half of these double nuclei are not visible in the HST B-band images due to dust obscuration. The majority of interacting LIRGs have remaining merger timescales of 0.3-1.3 Gyr, based on the projected nuclear separations and the mass ratio of nuclei. We find that the bulge luminosity surface density L_Bulge/R²_Bulge increases significantly along the merger sequence (primarily due to a decrease of the bulge radius), while the bulge luminosity shows a small increase toward late merger stages. No significant increase of the bulge Sersic index is found. LIRGs that show no interaction features have on average a significantly larger bulge luminosity, suggesting that non-merging LIRGs have larger bulge masses than merging LIRGs. This may be related to the flux-limited nature of the sample and the fact that mergers can significantly boost the IR luminosity of otherwise low luminosity galaxies. We find that the projected nuclear separation is significantly smaller for ULIRGs (median value of 1.2 kpc) than for LIRGs (median value of 6.7 kpc), suggesting that the LIRG phase appears earlier in mergers than the ULIRG phase.

[en] The detection of CO(1→0) emission in the massive (i.e., M _H ∼ -26.13 mag), z ∼ 0.3 host-galaxy system of the broad absorption line quasi-stellar object (QSO) PG1700+518 is reported. The host system has a CO luminosity of L'_CO ∼ 1.4 x 10¹⁰ K km s^-1 pc², and thus a star-forming molecular gas mass of M(H₂) ∼ 6 x 10¹⁰ M _sun (adopting an α = 4 M _sun [K km s^-1 pc²]^-1), making it one of the most molecular gas-rich Palomar-Green QSO hosts observed to date. New Hubble Space Telescope WFPC2 direct and NICMOS coronagraphic images show the highest resolution view yet of the host and companion. The new NICMOS image reveals the underlying, apparently tidally disrupted structure seen previously from high-resolution ground-based optical imaging. Light from the host galaxy is overwhelmed by the central point source in the WFPC2 images. The companion galaxy is well resolved in both data sets, and the WFPC2 provides for the first time a clear picture of the optically visible ring structure. The CO redshift is within the range of redshifts derived from optical QSO emission lines, thus the observed CO is associated with the QSO host. However, it cannot be ruled out that the companion has at least ∼10¹⁰ M _sun of molecular gas. Finally, if the far-infrared luminosity, which is 1/5 of the bolometric luminosity, is the luminosity of the starburst population, the star formation rate is estimated to be ∼210 M _sun yr^-1. There is thus sufficient molecular gas in the QSO host galaxy to fuel both star formation and QSO activity for another ∼10⁸ yr. We speculate that we may be witnessing the fueling event in progress that resulted from a collision between the QSO host and the companion galaxy, and that there is an accompanying expulsion of material along our line of sight in the form of broad absorption line gas.

[en] An analysis of data from the Spitzer Space Telescope, Hubble Space Telescope, Chandra X-ray Observatory, and AKARI Infrared Astronomy Satellite is presented for the z = 0.036 merging galaxy system II Zw 096 (CGCG 448-020). Because II Zw 096 has an infrared luminosity of log(L_IR/L_sun) = 11.94, it is classified as a Luminous Infrared Galaxy (LIRG), and was observed as part of the Great Observatories All-sky LIRG Survey (GOALS). The Spitzer data suggest that 80% of the total infrared luminosity comes from an extremely compact, red source not associated with the nuclei of the merging galaxies. The Spitzer mid-infrared spectra indicate no high-ionization lines from a buried active galactic nucleus in this source. The strong detection of the 3.3 μm and 6.2 μm polycyclic aromatic hydrocarbon emission features in the AKARI and Spitzer spectra also implies that the energy source of II Zw 096 is a starburst. Based on Spitzer infrared imaging and AKARI near-infrared spectroscopy, the star formation rate is estimated to be 120 M_sun yr^-1 and >45 M_sun yr^-1, respectively. Finally, the high-resolution B-, I-, and H-band images show many star clusters in the interacting system. The colors of these clusters suggest at least two populations-one with an age of 1-5 Myr and one with an age of 20-500 Myr, reddened by 0-2 mag of visual extinction. The masses of these clusters span a range between 10⁶ and 10⁸ M_sun. This starburst source is reminiscent of the extranuclear starburst seen in NGC 4038/9 (the Antennae Galaxies) and Arp 299 but approximately an order of magnitude more luminous than the Antennae. The source is remarkable in that the off-nuclear infrared luminosity dominates the entire system.

[en] Luminous (LIRGs; log (L_IR/L_☉) = 11.00-11.99) and ultraluminous infrared galaxies (ULIRGs; log (L_IR/L_☉) = 12.00-12.99) are the most extreme star-forming galaxies in the universe. The local (U)LIRGs provide a unique opportunity to study their multi-wavelength properties in detail for comparison with their more numerous counterparts at high redshifts. We present common large aperture photometry at radio through X-ray wavelengths and spectral energy distributions (SEDs) for a sample of 53 nearby (z < 0.083) LIRGs and 11 ULIRGs spanning log (L_IR/L_☉) = 11.14-12.57 from the flux-limited (f_60μm > 5.24 Jy) Great Observatories All-sky LIRG Survey. The SEDs for all objects are similar in that they show a broad, thermal stellar peak (∼0.3-2 μm), and a dominant FIR (∼40-200 μm) thermal dust peak, where νL_ν(60 μm)/νL_ν(V) increases from ∼2 to 30 with increasing L_IR. When normalized at IRAS 60 μm, the largest range in the luminosity ratio, R(λ) ≡ log[νL_ν(λ)/νL_ν(60 μm)], observed over the full sample is seen in the hard X-rays (HX = 2-10 keV), where ΔR_HX = 3.73 (R-bar_HX= -3.10). A small range is found in the radio (1.4 GHz), ΔR_1.4GHz = 1.75, where the mean ratio is largest, (R-bar_1.4GHz= -5.81). Total infrared luminosities, L_IR(8-1000 μm), dust temperatures, and dust masses were computed from fitting thermal dust emission modified blackbodies to the mid-infrared (MIR) through submillimeter SEDs. The new results reflect an overall ∼0.02 dex lower luminosity than the original IRAS values. Total stellar masses were computed by fitting stellar population synthesis models to the observed near-infrared (NIR) through ultraviolet (UV) SEDs. Mean stellar masses are found to be log (M_*/M_☉) = 10.79 ± 0.40. Star formation rates have been determined from the infrared (SFR_IR ∼ 45 M_☉ yr^–1) and from the monochromatic UV luminosities (SFR_UV ∼ 1.3 M_☉ yr^–1), respectively. Multi-wavelength active galactic nucleus (AGN) indicators have be used to select putative AGNs: About 60% of the ULIRGs would have been classified as an AGN by at least one of the selection criteria.

[en] 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 and Charlot simple stellar population model and Salpeter initial mass function, the age distribution of the clusters declines as $dN/d\mathrm{\tau <!--\; ??\; -->}={\mathrm{\tau <!--\; ??\; -->}}^{-<!--\; ???\; -->0.9+/-<!--\; ???\; -->0.3}$, consistent with the age distribution derived for the Antennae Galaxies, and interpreted as evidence for rapid cluster disruption occurring in the strong tidal fields of merging galaxies. The large number of ${10}^6{M}_{\odot <!--\; ???\; -->}$ 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.