K. Xu

GOALS: The Great Observatories All-Sky LIRG Survey

ABSTRACT.The Great Observatories All-Sky LIRG Survey (GOALS20) combines data from NASA’s Spitzer Space Telescope, Chandra X-Ray Observatory, Hubble Space Telescope (HST), and Galaxy Evolution Explorer (GALEX) observatories, together with ground-based data, into a comprehensive imaging and spectroscopic survey of over 200 low-redshift (zxa0<xa00.088z<0.088), Luminous Infrared Galaxies (LIRGs). The LIRGs are a complete subset of the IRAS Revised Bright Galaxy Sample (RBGS), which comprises 629 extragalactic objects with 60xa0μm flux densities above 5.24xa0Jy, and Galactic latitudes above five degrees. The LIRGs targeted in GOALS span the full range of nuclear spectral types defined via traditional optical line-ratio diagrams (type-1 and type-2 AGN, LINERs, and starbursts) as well as interaction stages (major mergers, minor mergers, and isolated galaxies). They provide an unbiased picture of the processes responsible for enhanced infrared emission in galaxies in the local Universe. As an example of the analytic powe...

THE BURIED STARBURST IN THE INTERACTING GALAXY II Zw 096 AS REVEALED BY THE SPITZER SPACE TELESCOPE

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_☉) = 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_☉ yr^(-1) and >45 M_☉ 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 10^6 and 10^8 M_☉. 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.

The Great Observatories All-Sky LIRG Survey: Herschel Image Atlas and Aperture Photometry

Far-infrared images and photometry are presented for 201 Luminous and Ultraluminous Infrared Galaxies [LIRGs: log (L_(IR)/L⊙) = 11.00-11.99, ULIRGs: log (L_(IR)/L⊙) = 12.00-12.99], in the Great Observatories All-Sky LIRG Survey (GOALS), based on observations with the Herschel Space Observatory Photodetector Array Camera and Spectrometer (PACS) and the Spectral and Photometric Imaging Receiver (SPIRE) instruments. The image atlas displays each GOALS target in the three PACS bands (70, 100, and 160 μm) and the three SPIRE bands (250, 350, and 500 μm), optimized to reveal structures at both high and low surface brightness levels, with images scaled to simplify comparison of structures in the same physical areas of ~100 × 100 kpc^2. Flux densities of companion galaxies in merging systems are provided where possible, depending on their angular separation and the spatial resolution in each passband, along with integrated system fluxes (sum of components). This data set constitutes the imaging and photometric component of the GOALS Herschel OT1 observing program, and is complementary to atlases presented for the Hubble Space Telescope, Spitzer Space Telescope, and Chandra X-ray Observatory. Collectively, these data will enable a wide range of detailed studies of active galactic nucleus and starburst activity within the most luminous infrared galaxies in the local universe.

MID-INFRARED PROPERTIES OF NEARBY LUMINOUS INFRARED GALAXIES I: SPITZER IRS SPECTRA FOR THE GOALS SAMPLE

The Great Observatories All-Sky LIRG Survey (GOALS) is a comprehensive, multiwavelength study of luminous infrared galaxies (LIRGs) in the local universe. Here we present low resolution Spitzer IRS spectra covering 5-38 µm and provide a basic analysis of the mid-IR spectral properties observed nfor nearby LIRGs. In a companion paper, we discuss detailed fits to the spectra and compare the LIRGs to other classes of galaxies. The GOALS sample of 244 nuclei in 180 luminous (10^(11)≤ L_(IR)=L^☉ 60%) of the GOALS LIRGs have high 6.2 µm PAH equivalent widths (EQW_(6.2µm) > 0.4 µm) and low levels of silicate absorption (s_(9.7µm) > -1.0). There is a general trend among the U/LIRGs for both silicate depth and mid-infrared (MIR) slope to increase with increasing nL_(IR). U/LIRGs in the late to final stages of a merger also have, on average, steeper MIR slopes and higher levels of dust obscuration. Together, these trends suggest that as gas & dust is funneled towards the center of a coalescing merger, the nuclei become more compact and more obscured. As a result, the dust temperature increases leading also to a steeper MIR slope. The sources that depart from nthese correlations have very low PAH equivalent width (EQW_(6.2µm) < 0.1 µm) consistent with their emission being dominated by an AGN in the MIR. These extremely low PAH equivalent width sources separate into two distinct types: relatively unobscured sources with a very hot dust component (and thus very shallow MIR slopes) and heavily dust obscured nuclei with a steep temperature gradient. nThe most heavily dust obscured sources are also the most compact in their MIR emission, suggesting that the obscuring (cool) dust is associated with the outer regions of the starburst and not simply a measure of the dust along the line of sight through a large, dusty disk. A marked decline is seen for the fraction of high EQW (star formation dominated) sources as the merger progresses. The decline is accompanied by an increase in the fraction of composite sources while the fraction of sources where an nAGN dominates the MIR emission remains low. When compared to the MIR spectra of submillimeter galaxies (SMGs) at z~2, both the average GOALS LIRG and ULIRG spectra are more absorbed at 9.7 µm and the average GOALS LIRG has more PAH emission. However, when the AGN contributions to both the local GOALS LIRGs and the high-z SMGs are removed, the average local starbursting LIRG closely resembles the starburst-dominated SMGs.

Mid-infrared Properties of Nearby Luminous Infrared Galaxies. I. Spitzer Infrared Spectrograph Spectra for the GOALS Sample

The Great Observatories All-Sky LIRG Survey (GOALS) is a comprehensive, multiwavelength study of luminous infrared galaxies (LIRGs) in the local universe. Here we present low resolution Spitzer IRS spectra covering 5-38 µm and provide a basic analysis of the mid-IR spectral properties observed nfor nearby LIRGs. In a companion paper, we discuss detailed fits to the spectra and compare the LIRGs to other classes of galaxies. The GOALS sample of 244 nuclei in 180 luminous (10^(11)≤ L_(IR)=L^☉ 60%) of the GOALS LIRGs have high 6.2 µm PAH equivalent widths (EQW_(6.2µm) > 0.4 µm) and low levels of silicate absorption (s_(9.7µm) > -1.0). There is a general trend among the U/LIRGs for both silicate depth and mid-infrared (MIR) slope to increase with increasing nL_(IR). U/LIRGs in the late to final stages of a merger also have, on average, steeper MIR slopes and higher levels of dust obscuration. Together, these trends suggest that as gas & dust is funneled towards the center of a coalescing merger, the nuclei become more compact and more obscured. As a result, the dust temperature increases leading also to a steeper MIR slope. The sources that depart from nthese correlations have very low PAH equivalent width (EQW_(6.2µm) < 0.1 µm) consistent with their emission being dominated by an AGN in the MIR. These extremely low PAH equivalent width sources separate into two distinct types: relatively unobscured sources with a very hot dust component (and thus very shallow MIR slopes) and heavily dust obscured nuclei with a steep temperature gradient. nThe most heavily dust obscured sources are also the most compact in their MIR emission, suggesting that the obscuring (cool) dust is associated with the outer regions of the starburst and not simply a measure of the dust along the line of sight through a large, dusty disk. A marked decline is seen for the fraction of high EQW (star formation dominated) sources as the merger progresses. The decline is accompanied by an increase in the fraction of composite sources while the fraction of sources where an nAGN dominates the MIR emission remains low. When compared to the MIR spectra of submillimeter galaxies (SMGs) at z~2, both the average GOALS LIRG and ULIRG spectra are more absorbed at 9.7 µm and the average GOALS LIRG has more PAH emission. However, when the AGN contributions to both the local GOALS LIRGs and the high-z SMGs are removed, the average local starbursting LIRG closely resembles the starburst-dominated SMGs.

MID-INFRARED PROPERTIES OF NEARBY LUMINOUS INFRARED GALAXIES. I.SPITZERINFRARED SPECTROGRAPH SPECTRA FOR THE GOALS SAMPLE

The Great Observatories All-Sky LIRG Survey (GOALS) is a comprehensive, multiwavelength study of luminous infrared galaxies (LIRGs) in the local universe. Here we present low resolution Spitzer IRS spectra covering 5-38 µm and provide a basic analysis of the mid-IR spectral properties observed nfor nearby LIRGs. In a companion paper, we discuss detailed fits to the spectra and compare the LIRGs to other classes of galaxies. The GOALS sample of 244 nuclei in 180 luminous (10^(11)≤ L_(IR)=L^☉ 60%) of the GOALS LIRGs have high 6.2 µm PAH equivalent widths (EQW_(6.2µm) > 0.4 µm) and low levels of silicate absorption (s_(9.7µm) > -1.0). There is a general trend among the U/LIRGs for both silicate depth and mid-infrared (MIR) slope to increase with increasing nL_(IR). U/LIRGs in the late to final stages of a merger also have, on average, steeper MIR slopes and higher levels of dust obscuration. Together, these trends suggest that as gas & dust is funneled towards the center of a coalescing merger, the nuclei become more compact and more obscured. As a result, the dust temperature increases leading also to a steeper MIR slope. The sources that depart from nthese correlations have very low PAH equivalent width (EQW_(6.2µm) < 0.1 µm) consistent with their emission being dominated by an AGN in the MIR. These extremely low PAH equivalent width sources separate into two distinct types: relatively unobscured sources with a very hot dust component (and thus very shallow MIR slopes) and heavily dust obscured nuclei with a steep temperature gradient. nThe most heavily dust obscured sources are also the most compact in their MIR emission, suggesting that the obscuring (cool) dust is associated with the outer regions of the starburst and not simply a measure of the dust along the line of sight through a large, dusty disk. A marked decline is seen for the fraction of high EQW (star formation dominated) sources as the merger progresses. The decline is accompanied by an increase in the fraction of composite sources while the fraction of sources where an nAGN dominates the MIR emission remains low. When compared to the MIR spectra of submillimeter galaxies (SMGs) at z~2, both the average GOALS LIRG and ULIRG spectra are more absorbed at 9.7 µm and the average GOALS LIRG has more PAH emission. However, when the AGN contributions to both the local GOALS LIRGs and the high-z SMGs are removed, the average local starbursting LIRG closely resembles the starburst-dominated SMGs.