An IRAS High Resolution Image Restoration (HIRES) Atlas of All Interacting Galaxies in the IRAS Revised Bright Galaxy Sample

We present high-resolution (30"-1') 12, 25, 60, and 100 micron images of 106 interacting galaxy systems contained in the IRAS Revised Bright Galaxy Sample (RBGS, Sanders et al. 2003), a complete sample of all galaxies having a 60 micron flux density greater than 5.24 Jy. These systems were selected to have at least two distinguishable galaxies separated by less than three average galactic diameters, and thus we have excluded very widely separated systems and very advanced mergers. The new complete survey has the same properties as the prototype survey of Surace et al. 1993. We find no increased tendency for infrared-bright galaxies to be associated with other infrared bright galaxies among the widely separated pairs studied here. We find small enhancements in far-infrared activity in multiple galaxy systems relative to RBGS non-interacting galaxies with the same blue luminosity distribution. We also find no differences in infrared activity (as measured by infrared color and luminosity) between late and early-type spiral galaxies.Comment: 49 pages, 13 figures. To appear in the Astronomical Journal. Figures have been degraded due to space considerations. A PDF version with higher quality figures is available at http://humu.ipac.caltech.edu/~jason/pubs/surace_hires.pd

Resolved CO(1-0) Nuclei in IRAS 14348-1447: Evidence for Massive Bulge Progenitors to Ultraluminous Infrared Galaxies

High-resolution, CO(1-0) interferometry of the ultraluminous infrared galaxy IRAS 14348-1447 is presented. The merger system has a molecular gas mass of \~3x10^10 solar masses and a projected nuclear separation of 4.8 kpc (3.5"), making it one of the most molecular gas-rich galaxies known and an ideal candidate for studying the intermediate stages of an ultraluminous merger event. The CO morphology shows two molecular gas components associated with the stellar nuclei of the progenitors, consistent with the idea that the molecular disks are gravitationally bound by the dense bulges of the progenitor galaxies as the interaction proceeds. In contrast, less luminous infrared galaxies observed to date with projected nuclear separations of ~<5 kpc show a dominant CO component between the stellar nuclei. This discrepancy may be an indication that the progenitors of mergers with lower infrared luminosity do not possess massive bulges, and that the gas is stripped during the initial encounter of their progenitors. A comparison of the CO and radio luminosities of the NE and SW component show them to have comparable radio and CO flux ratios of f(NE)/f(SW) ~0.6, possibly indicating that the amount of star-forming molecular gas in the progenitors is correlated with the supernovae rate. The estimate of molecular gas masses of the nuclei and the extent of the radio emission are used to infer that the nuclei of IR 14348-1447 have gas densities comparable to the cores of elliptical galaxies.Comment: LaTex, 5 pages with 1 postscript and 1 jpg figure, ApJ Letters, in pres

High Spatial Resolution Near-Ir Tip/Tilt Imaging Of "Warm" Ultraluminous Infrared Galaxies

We present results from high spatial resolution (FWHM ≈ 0.3–0.5 ″) near-IR (1.6 and 2.1μm) imaging of a complete sample of ultraluminous infrared galaxies (ULIGs) chosen to have “warm” mid-IR colors (f_(25)/f_(60) > 0.2) characteristic of AGN. In conjunction with our WFPC2 imaging program (Surace et al. 1998), we have found that nearly all of these systems are advanced mergers with complex nuclear morphologies. The extended underlying galaxies are detected in each system at H and K′, and are found to have luminosities of a few L*, similar to quasars (McLeod & Rieke 1994). Many of the circumnuclear star-forming knots seen at optical wavelengths have been detected. Based on model SEDs, their bolometric luminosities appear similar to those of the extended nuclear starbursts seen in other, less-luminous interacting systems (i.e. NGC 4038/9). Each ULIG is increasingly dominated at long wavelengths by a compact source which we identify as a putative active nucleus. The optical/near-IR colors of these putative nuclei are more extreme than the most infrared-active starburst galaxies, yet are identical to “far-IR loud” quasars which are in turn similar to optical quasars with significant hot (800 K) dust emission. Half of the ULIGs have dereddened nuclear near-IR luminosities comparable to those of QSOs, while the others resemble Seyferts; this may be an effect of patchy extinction and scattering. Similarities between the putative ULIG nuclei and QSO nuclei, the underlying host galaxies, and the apparent young age of the ULIGs (as evidenced by their compact star-forming knots) support the evolution of “warm” ULIGs into optical QSOs

Spitzer Mid-Infrared Imaging of Nearby Ultraluminous Infrared Galaxies

We have observed 14 nearby (z<0.16) Ultraluminous Infrared Galaxies (ULIRGs) with Spitzer at 3.6-24 microns. The underlying host galaxies are well-detected, in addition to the luminous nuclear cores. While the spatial resolution of Spitzer is poor, the great sensitivity of the data reveals the underlying galaxy merger remnant, and provides the first look at off-nuclear mid-infrared activity.Comment: To appear in the conference proceedings for Spitzer New Views of the Universe, held Nov. 2004 in Pasadena, C

The IRAS Revised Bright Galaxy Sample (RBGS)

IRAS flux densities, redshifts, and infrared luminosities are reported for all sources identified in the IRAS Revised Bright Galaxy Sample (RBGS), a complete flux-limited survey of all extragalactic objects with total 60 micron flux density greater than 5.24 Jy, covering the entire sky surveyed by IRAS at Galactic latitude |b| > 5 degrees. The RBGS includes 629 objects, with a median (mean) sample redshift of 0.0082 (0.0126) and a maximum redshift of 0.0876. The RBGS supersedes the previous two-part IRAS Bright Galaxy Samples, which were compiled before the final ("Pass 3") calibration of the IRAS Level 1 Archive in May 1990. The RBGS also makes use of more accurate and consistent automated methods to measure the flux of objects with extended emission. Basic properties of the RBGS sources are summarized, including estimated total infrared luminosities, as well as updates to cross-identifications with sources from optical galaxy catalogs established using the NASA/IPAC Extragalactic Database (NED). In addition, an atlas of images from the Digitized Sky Survey with overlays of the IRAS position uncertainty ellipse and annotated scale bars is provided for ease in visualizing the optical morphology in context with the angular and metric size of each object. The revised bolometric infrared luminosity function, phi(L_ir), for infrared bright galaxies in the local Universe remains best fit by a double power law, phi(L_ir) ~ L_ir^alpha, with alpha = -0.6 (+/- 0.1), and alpha = -2.2 (+/- 0.1) below and above the "characteristic" infrared luminosity L_ir ~ 10^{10.5} L_solar, respectively. (Abridged)Comment: Accepted for publication in the Astronomical Journal. Contains 50 pages, 7 tables, 16 figures. Due to astro-ph space limits, only 1 of 26 pages of Figure 1, and 1 of 11 pages of Table 7, are included; full resolution Postscript files are available at http://nedwww.ipac.caltech.edu/level5/March03/IRAS_RBGS/Figures/ . Replacement: Corrected insertion of Fig. 15 (MethodCodes.ps) in LaTe

High Resolution Optical/Near-Infrared Imaging of Cool Ultraluminous Infrared Galaxies

We present high spatial resolution (FWHM 0.3-0.8") BIHK'-band imaging of a sample of ultraluminous infrared galaxies with "cool" mid-infrared colors (f25/f60 < 0.2) which select against AGN-like systems and which form a complementary sample to the "warm" ULIGs of Surace et al. (1998). We find that all of the cool ULIGs are either advanced mergers or are pre-mergers with evidence for still-separate nuclei with separations greater than 600 pc. Extended tidal features such as tails and loops as well as clustered star formation are observed in most systems. This extended tidal structure suggests a common progenitor geometry for most of the ULIGs: a plunging disk collision where the disks are highly inclined with respect to each other. The underlying host galaxies have H-band luminosities of 1-2.5 L*, very similar to that found in the "warm" ULIGs. The nuclear regions of these galaxies have morphologies and colors characteristic of a recent burst of star formation mixed with hot dust and mildly extinguished by A_v=2-5 magnitudes; only in o ne case (IRAS 22491-1808) is there evidence for a compact emission region with colors similar to an extinguished QSO. Most of the observed star-forming knots appear to have very young (10 Myr) ages based on their optical/near-infrared colors. These star-forming knots are insufficiently luminous to typically provide more than 10% of the high bolometric luminosity of the systems

Molecular Gas and Nuclear Activity in Ultraluminous Infrared Galaxies with Double Nuclei

High-resolution CO(1-0) observations of five ultraluminous infrared galaxies (ULIGs: L_IR [8-1000um] >~ 10^12 L_sun) with double nuclei are analyzed. These sources constitute a complete subset of local ULIGs expected to be in an intermediate stage of merging and selected with projected nuclear separations of 2.0-5.4 (3-5 kpc) so they could be resolved with the Owens Valley Radio Observatory Millimeter Array. The observed pairs include two mergers with cool far-infrared colors (25um to 60um flux density ratio f_25um/f_60um ~ 0.2) selected from the IRAS Warm Galaxy Sample (IRAS 08572+3915, IRAS 13451+1232 = PKS 1345+12, and IRAS 13536+1836 = Mrk 463). These ULIGs are further distinguished by the presence of pairs of active nuclei; among the ten nuclei, nine have Seyfert or LINER classifications and one is unclassified. Molecular gas is detected only on the redder, more radio-luminous nucleus of the warm objects, whereas both nuclei of the cool ULIGs are detected in CO. The inferred molecular gas masses for the detected nuclei are 0.1-1.2x10^10 M_sun, and the undetected nuclei have molecular gas masses at least 1.2--2.8 times less than that of their CO-luminous companions. Upper limits on the extent of the CO emitting regions of each detected nucleus range from 2--4 kpc, which is about 3-6 times smaller than the average effective CO diameter of nearby spiral galaxies..