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 ...Infrared Spectrograph spectra covering 5-38 mu m and provide a basic analysis of the mid-IR spectral properties observed for nearby LIRGs. In a companion paper, we discuss detailed fits to the spectra and compare the LIRGs to other classes of galaxies. 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 mu m 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.
ABSTRACT We present luminosity functions derived from a spectroscopic survey of active galactic nuclei (AGNs) selected from Spitzer Space Telescope imaging surveys. Selection in the mid-infrared is ...significantly less affected by dust obscuration. We can thus compare the luminosity functions of obscured and unobscured AGNs in a more reliable fashion than by using optical or X-ray data alone. We find that the AGN luminosity function can be well described by a broken power-law model in which the break luminosity decreases with redshift. At high redshifts ( ), we find significantly more AGNs at a given bolometric luminosity than found by either optical quasar surveys or hard X-ray surveys. The fraction of obscured AGNs decreases rapidly with increasing AGN luminosity, but, at least at high redshifts, appears to remain at % even at bolometric luminosities . The data support a picture in which the obscured and unobscured populations evolve differently, with some evidence that high luminosity obscured quasars peak in space density at a higher redshift than their unobscured counterparts. The amount of accretion energy in the universe estimated from this work suggests that AGNs contribute about 12% to the total radiation intensity of the universe, and a high radiative accretion efficiency is required to match current estimates of the local mass density in black holes.
We present our initial results on the CO rotational spectral line energy distribution (SLED) of the J to J-1 transitions from J = 4 up to 13 from Herschel SPIRE spectroscopic observations of 65 ...luminous infrared galaxies (LIRGs) in the Great Observatories All-Sky LIRG Survey. The observed SLEDs change on average from one peaking at J < or =, slant 4 to a broad distribution peaking around J ~ 6 to 7 as the IRAS 60-to-100 mu m color, C(60/100), increases. However, the ratios of a CO line luminosity to the total infrared luminosity, L sub(IR), show the smallest variation for J around 6 or 7. This suggests that, for most LIRGs, ongoing star formation (SF) is also responsible for a warm gas component that emits CO lines primarily in the mid-J regime (5 <, ~ J <, ~ 10). As a result, the logarithmic ratios of the CO line luminosity summed over CO (5-4), (6-5), (7-6), (8-7) and (10-9) transitions to L sub(IR), log R sub(midCO), remain largely independent of C(60/100), and show a mean value of -4.13 (= log (ProQuest: Formulae and/or non-USASCII text omitted)) and a sample standard deviation of only 0.10 for the SF-dominated galaxies. Including additional galaxies from the literature, we show, albeit with a small number of cases, the possibility that galaxies, which bear powerful interstellar shocks unrelated to the current SF, and galaxies, in which an energetic active galactic nucleus contributes significantly to the bolometric luminosity, have their R sub(midCO) higher and lower than (ProQuest: Formulae and/or non-USASCII text omitted) respectively.
We present the results of a program of optical and near-infrared spectroscopic follow-up of candidate active galactic nuclei (AGNs) selected in the mid-infrared. This survey selects both normal and ...obscured AGNs closely matched in luminosity across a wide range, from Seyfert galaxies with bolometric luminosities L sub(bol) ~ 10 super(10) L sub(middot in circle) to highly luminous quasars (L sub(bol) ~ 10 super(14) L sub(middot in circle)), all with redshifts ranging from 0 to 4.3. Samples of candidate AGNs were selected with mid-infrared color cuts at several different 24 mu m flux density limits to ensure a range of luminosities at a given redshift. The survey consists of 786 candidate AGNs and quasars, of which 672 have spectroscopic redshifts and classifications. Of these, 137 (20%) are type 1 AGNs with blue continua, 294 (44%) are type 2 objects with extinctions A sub(v) > ~ 5 toward their AGNs, 96 (14%) are AGNs with lower extinctions (A sub(v) ~ 1), and 145 (22%) have redshifts, but no clear signs of AGN activity in their spectra. Of the survey objects 50% have L sub(bol) > 10 super(12) L sub(middot in circle), in the quasar regime. We present composite spectra for type 2 quasars and objects with no signs of AGN activity in their spectra. We also discuss the mid-infrared-emission-line luminosity correlation and present the results of cross correlations with serendipitous X-ray and radio sources. The results show that: (1) obscured objects dominate the overall AGN population, (2) mid-infrared selected AGN candidates exist which lack AGN signatures in their optical spectra but have AGN-like X-ray or radio counterparts, and (3) X-ray and optical classifications of obscured and unobscured AGNs often differ.
We present results from the second part of our analysis of the extended mid-infrared (MIR) emission of the GOALS sample based on 5-14 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 all galaxies in the sample, FEE Delta *l, defined as the fraction of the emission that originates outside of the unresolved central component of a source, and spatially separate the MIR spectrum of a galaxy into its nuclear and extended components. We find that the Ne II12.81 Delta *mm emission line is as compact as the hot dust MIR continuum, while the polycyclic aromatic hydrocarbon (PAH) emission is more extended. In addition, the 6.2 and 7.7 Delta *mm PAH emission is more compact than that of the 11.3 Delta *mm PAH, which is consistent with the formers being enhanced in a more ionized medium. The presence of an active galactic nucleus (AGN) or a powerful nuclear starburst increases the compactness and the luminosity surface density of the hot dust MIR continuum, but has a negligible effect on the spatial extent of the PAH emission on kpc-scales. Furthermore, it appears that both processes, AGN and/or nuclear starburst, are indistinguishable in terms of how they modify the integrated PAH-to-continuum ratio of the FEE in (ultra)luminous infrared galaxies ((U)LIRGs). Globally, the 5-14 Delta *mm spectra of the extended emission component are homogeneous for all galaxies in the GOALS sample. This suggests that, independently of the spatial distribution of the various MIR features, the physical properties of star formation occurring at distances farther than 1.5 kpc from the nuclei of (U)LIRGs are very similar, resembling local star-forming galaxies with L IR < 1011 L , as well as star-formation-dominated ULIRGs at z ~ 2. In contrast, the MIR spectra of the nuclear component of local ULIRGs and LIRGs are very diverse. These results imply that the observed variety of the integrated MIR properties of local (U)LIRGs arise, on average, only from the processes that are taking place in their cores.
We present Hubble Space Telescope images and spectral energy distributions from optical to infrared wavelengths for a sample of six 0.3 < z < 0.8 type 2 quasars selected in the mid-infrared using ...data from the Spitzer Space Telescope. All the host galaxies show some signs of disturbance. Most seem to possess dusty, star-forming disks. The disk inclination, estimated from the axial ratio of the hosts, correlates with the depth of the silicate feature in the mid-infrared spectra, implying that at least some of the reddening toward the AGN arises in the host galaxy. The star formation rates in these objects, as inferred from the strengths of the PAH features and far-infrared continuum, range from 3 to 90 M unk yr super(-1), but are mostly much larger than those inferred from the 0 II A3727 emission-line luminosity, due to obscuration. Taken together with studies of type 2 quasar hosts from samples selected in the optical and X-ray, this is consistent with previous suggestions that two types of extinction processes operate within the type 2 quasar population, namely, a component due to the dusty torus in the immediate environment of the AGN, and a more extended component due to a dusty, star-forming disk.
We present excellent-resolution and high-sensitivity Very Large Array observations of the 21 cm H I line emission from the face-on galaxy NGC 1058, providing the first reliable study of the H I ...profile shapes throughout the entire disk of an external galaxy. Our observations show an intriguing picture of the interstellar medium; throughout this galaxy velocity dispersions range between 4 and 15 km s-1 but are not correlated with star formation, stars, or the gaseous spiral arms. The velocity dispersions decrease with radius, but this global trend has a large scatter as there are several isolated, resolved regions of high dispersion. The decline of starlight with radius is much steeper than that of the velocity dispersions or that of the energy in the gas motions.
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.
We present a statistical analysis of the mid-infrared (MIR) spectra of 248 luminous infrared (IR) galaxies (LIRGs) which comprise the Great Observatories All-sky LIRG Survey (GOALS) observed with the ...Infrared Spectrograph (IRS) on board the Spitzer Space Telescope. The GOALS sample enables a direct measurement of the relative contributions of star formation and active galactic nuclei (AGNs) to the total IR emission from a large sample of local LIRGs. The AGN contribution to the MIR emission (f AGN) is estimated by employing several diagnostics based on the properties of the Ne V, O IV, and Ne II fine-structure gas emission lines, the 6.2 Delta *mm polycyclic aromatic hydrocarbon (PAH), and the shape of the MIR continuum. We find that 18% of all LIRGs contain an AGN and that in 10% of all sources the AGN contributes more than 50% of the total IR luminosity. Summing up the total IR luminosity contributed by AGNs in all our sources suggests that AGNs supply ~12% of the total energy emitted by LIRGs. The average spectrum of sources with an AGN looks similar to the average spectrum of sources without an AGN, but it has lower PAH emission and a flatter MIR continuum. AGN-dominated LIRGs have higher IR luminosities, warmer MIR colors, and are found in interacting systems more often than pure starburst LIRGs. However, we find no linear correlations between these properties and f AGN. We used the IRAC colors of LIRGs to confirm that finding AGNs on the basis of their MIR colors may miss ~40% of AGN-dominated (U)LIRGs.
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