The Great Observatories All-sky LIRG Survey (GOALS) consists of a complete sample of 202 luminous infrared galaxies (LIRGs) selected from the IRAS Revised Bright Galaxy Sample (RBGS). The galaxies ...span the full range of interaction stages, from isolated galaxies to interacting pairs to late stage mergers. We present a comparison of the UV and infrared properties of 135 galaxies in GOALS observed by GALEX and Spitzer. For interacting galaxies with separations greater than the resolution of GALEX and Spitzer (~2''-6''), we assess the UV and IR properties of each galaxy individually. The contribution of the FUV to the measured star formation rate (SFR) ranges from 0.2% to 17.9%, with a median of 2.8% and a mean of 4.0% ± 0.4%. The specific star formation rate (SSFR) of the GOALS sample is extremely high, with a median value (3.9 × 10-10 yr-1) that is comparable to the highest SSFRs seen in the Spitzer Infrared Nearby Galaxies Survey sample. We examine the position of each galaxy on the IR excess-UV slope (IRX-beta) diagram as a function of galaxy properties, including IR luminosity and interaction stage. The LIRGs on average have greater IR excesses than would be expected based on their UV colors if they obeyed the same relations as starbursts with L IR < 1011 L sun or normal late-type galaxies. The ratio of L IR to the value one would estimate from the IRX-beta relation published for lower luminosity starburst galaxies ranges from 0.2 to 68, with a median value of 2.7. A minimum of 19% of the total IR luminosity in the RBGS is produced in LIRGs and ultraluminous infrared galaxies with red UV colors (beta>0). Among resolved interacting systems, 32% contain one galaxy which dominates the IR emission while the companion dominates the UV emission. Only 21% of the resolved systems contain a single galaxy which dominates both wavelengths.
The properties of galaxies that are lower in surface brightness than the
dark night sky are reviewed. There are substantial selection effects against
the discovery of galaxies that are unevolved or ...diffuse; these systems are
missing from most wide field catalogs. Low surface brightness galaxies make up
a significant amount of the luminosity density of the local universe. They
contribute substantial but poorly determined amounts to the census of baryons
and dark matter. Low surface brightness galaxies are also relevant to the
interpretation of quasar absorption lines and to the understanding of rapidly
evolving galaxy populations in the more distant universe. Theories of galaxy
formation and evolution must accomodate the properties of these diffuse stellar
systems.
We present a study of the nearby Seyfert galaxy NGC 1068 using mid- and far-infrared data acquired with the IRAC, IRS, and MIPS instruments aboard the Spitzer Space Telescope. The images show ...extensive 8 and 24 mm emission coinciding with star formation in the inner spiral approximately 15'' (1 kpc) from the nucleus and a bright complex of star formation ~47'' (3 kpc) southwest of the nucleus. The brightest 8 mm polycyclic aromatic hydrocarbon (PAH) emission regions coincide remarkably well with knots observed in an Ha image. Strong PAH features at 6.2, 7.7, 8.6, and 11.3 mm are detected in IRS spectra measured at numerous locations inside, within, and outside the inner spiral. The IRAC colors and IRS spectra of these regions rule out dust heated by the active galactic nucleus (AGN) as the primary emission source; the spectral energy distributions are dominated by starlight and PAH emission. The equivalent widths and flux ratios of the PAH features in the inner spiral are generally consistent with conditions in a typical spiral galaxy interstellar medium (ISM). Interior to the inner spiral, the influence of the AGN on the ISM is evident via PAH flux ratios indicative of a higher ionization parameter and a significantly smaller mean equivalent width than observed in the inner spiral. The brightest 8 and 24 mm emission peaks in the disk of the galaxy, even at distances beyond the inner spiral, are located within the ionization cones traced by O III/Hb, and they are also remarkably well aligned with the axis of the radio jets. Although it is possible that radiation from the AGN may directly enhance PAH excitation or trigger the formation of OB stars that subsequently excite PAH emission at these locations in the inner spiral, the orientation of collimated radiation from the AGN and star formation knots in the inner spiral could be coincidental. The brightest PAH- and 24 mm-emitting regions are also located precisely where two spiral arms of molecular gas emerge from the ends of the inner stellar bar; this is consistent with kinematic models that predict maxima in the accumulation and compression of the ISM, where gas gets trapped within the inner Lindblad resonance of a large stellar bar that contains a smaller, weaker bar.
We present an analysis of the extended mid-infrared (MIR) emission of the Great Observatories All-Sky LIRG Survey sample based on 5-15 Delta *mm low-resolution spectra obtained with the Infrared ...Spectrograph on Spitzer. We calculate the fraction of extended emission (FEE) as a function of wavelength for the galaxies in the sample, FEE Delta *l, defined as the fraction of the emission which originates outside of the unresolved component of a source at a given distance. We find that the FEE Delta *l varies from one galaxy to another, but we can identify three general types of FEE Delta *l: one where FEE Delta *l is constant, one where features due to emission lines and polycyclic aromatic hydrocarbons appear more extended than the continuum, and a third which is characteristic of sources with deep silicate absorption at 9.7 Delta *mm. More than 30% of the galaxies have a median FEE Delta *l larger than 0.5, implying that at least half of their MIR emission is extended. Luminous Infrared Galaxies (LIRGs) display a wide range of FEE in their warm dust continuum (0 FEE13.2 Delta *mm 0.85). The large values of FEE13.2 Delta *mm that we find in many LIRGs suggest that the extended component of their MIR continuum emission originates in scales up to 10 kpc and may contribute as much as the nuclear region to their total MIR luminosity. The mean size of the LIRG cores at 13.2 Delta *mm is 2.6 kpc. However, once the IR luminosity of the systems reaches the threshold of L IR ~ 1011.8 L , slightly below the regime of Ultra-luminous Infrared Galaxies (ULIRGs), all sources become clearly more compact, with FEE13.2 Delta *mm 0.2, and their cores are unresolved. Our estimated upper limit for the core size of ULIRGs is less than 1.5 kpc. Furthermore, our analysis indicates that the compactness of systems with L IR 1011.25 L strongly increases in those classified as mergers in their final stage of interaction. The FEE13.2 Delta *mm is also related to the contribution of an active galactic nucleus (AGN) to the MIR emission. Galaxies which are more AGN dominated are less extended, independently of their L IR. We finally find that the extent of the MIR continuum emission is correlated with the far-IR IRAS log(f 60 Delta *mm/f 100 Delta *mm) color. This enables us to place a lower limit to the area in a galaxy from where the cold dust emission may originate, a prediction which can be tested soon with the Herschel 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 Delta *mm and 6.2 Delta *mm 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 106 and 108 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.
In 20 years, low-surface-brightness (LSB) galaxies have evolved from being an idiosyncratic notion to being one of the major baryonic repositories in the Universe. The story of their discovery and ...the characterization of their properties is told here. Their recovery from the noise of the night-sky background is a strong testament to the severity of surface-brightness selection effects. LSB galaxies have a number of remarkable properties which distinguish them from the more familiar Hubble sequence of spirals. The two most important are (1) they evolve at a significantly slower rate and may well experience star formation outside of the molecular-cloud environment, (2) they are embedded in dark-matter halos which are of lower density and more extended than the halos around high-surface-brightness (HSB) disk galaxies. Compared to HSB disks, LSB disks are strongly dark-matter dominated at all radii and show a systematic increase in M/L with decreasing central surface brightness. In addition, the recognition that large numbers of LSB galaxies actually exist has changed the form of the galaxy luminosity function and has clearly increased the space density of galaxies at z = 0. Recent CCD surveys have uncovered a population of red LSB disks that may be related to the excess of faint blue galaxies detected at moderate redshifts. LSB galaxies offer us a new window into galaxy evolution and formation which is every bit as important as those processes which have produced easy-to-detect galaxies. Indeed, the apparent youth of some LSB galaxies suggest that galaxy formation is a greatly extended process. While the discovery of LSB galaxies has led to new insights, it remains unwise to presume that we now have a representative sample which encompasses all galaxy types and forms.
The Arecibo Galaxy Environment Survey (AGES) is one of several H i surveys utilizing the new Arecibo L-band Feed Array (ALFA) fitted to the 305-m radio telescope at Arecibo. The survey is ...specifically designed to investigate various galactic environments to higher sensitivity, higher velocity resolution and higher spatial resolution than previous fully sampled, 21-cm multibeam surveys. The emphasis is on making detailed observations of nearby objects although the large system bandwidth (100 MHz) will allow us to quantify the H i properties over a large instantaneous velocity range. In this paper, we describe the survey and its goals and present the results from the precursor observations of a 5 × 1-deg2 region containing the nearby (∼10 Mpc) NGC 628 group. We have detected all the group galaxies in the region including the low-mass (MH I∼107 M⊙) dwarf, dw0137+1541. The fluxes and velocities for these galaxies compare well with previously published data. There is no intragroup neutral gas detected down to a limiting column density of 2 × 1018 cm−2. In addition to the group galaxies we have detected 22 galaxies beyond the NGC 628 group, nine of which are previously uncatalogued. We present the H i data for these objects and also SuperCOSMOS images for possible optical galaxies that might be associated with the H i signal. We have used V/Vmax analysis to model how many galaxies beyond 1000 km s−1 should be detected and compare this with our results. The predicted number of detectable galaxies varies depending on the H i mass function (HIMF) used in the analysis. Unfortunately the precursor survey area is too small to determine whether this is saying anything fundamental about the HIMF or simply highlighting the effect of low number statistics. This is just one of many questions that will be addressed by the complete AGES survey.
Using recent precision measurements of cosmological parameters, we re-examine whether these observations alone, independent of type Ia supernova surveys, are sufficient to imply the existence of dark ...energy. We find that best measurements of the age of the Universe t0, the Hubble parameter H0 and the matter fraction Ωm strongly favor an equation of state defined by (w<−1/3). This result is consistent with the existence of a repulsive, acceleration-causing component of energy if the Universe is nearly flat.
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