Optical and IR luminosity functions of IRAS galaxies
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The optical and infrared luminosity functions are determined for a 60 micron flux-limited sample of 68 IRAS galaxies covering a total area of 150 deg sq. The IR function is in good agreement with that obtained by other authors. The shape of the optical luminosity function is similar to that of optically selected galaxy samples. The integrated light of most objects in the sample have (NII) to H alpha line flux ratios characteristic of HII-region galaxies. In the absolute magnitude range M sub J = -18, -22 about 14% of late-type galaxies are IRAS galaxies. The apparent companionship frequency is about twice as large as that for a comparable sample of non-IRAS late-type galaxies.Cite
I have applied newly available optical emission line diagnostics to two samples of infrared-luminous galaxies in a program to discriminate between possible energy generation mechanisms, i.e., active nuclei and starbursts. The first sample was composed of very faint (F(60 microns) < 180 mJy, z < 0.3) galaxies drawn from coadded IRAS scans of the North Ecliptic Pole Region (NEPR). The second sample consisted of 37 much brighter sources drawn from the IRAS Bright Galaxy Sample (BGS). Analysis of the redshift distribution of the NEPR sample revealed clustering is present on scales ~10 Mpc. In addition, a very strong cluster was identified at z=0.088 that has a surface density roughly three times greater than the Great Wall. Out of the 76 galaxies observed from the NEPR sample 17 had strong spectra suitable for the analysis, which was based on the relative intensities of forbidden and permitted emission lines. While 3 sources could be classified as AGNs and another 7 as starburst galaxies, the remaining 7 eluded classification. Longslit optical emission-line spectra, which effectively separated nuclear and disk contributions to the emission, indicated the BGS galaxies contained 7 AGNs and 24 starbursts. In a minority of 6 cases, however, the line diagnostics failed to unambiguously classify the luminosity source. Follow-up near-infrared imaging showed that the 'straddlers' have redder near-infrared colors than the other BGS galaxies. The optical spectra and near-infrared colors taken together with morphological peculiarities imply that the straddlers are composite objects harboring low-luminosity active nuclei residing within starburst disks. Finally, the optical spectrum of a high redshift IRAS galaxy was analysed. IRAS 18003+6652 is the third most distant (z=0.088) galaxy known to have been observed by IRAS and has an unusually strong emission line spectrum in combination with low-ionization absorption features.
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We combine Herschel Photodetector Array Camera and Spectrometer and Spectral and Photometric Imaging Receiver maps of the full 2 deg2 Cosmic Evolution Survey (COSMOS) field with existing multi-wavelength data to obtain template and model-independent optical-to-far-infrared spectral energy distributions (SEDs) for 4218 Herschel-selected sources with log(LIR/L☉) = 9.4–13.6 and z = 0.02–3.54. Median SEDs are created by binning the optical to far-infrared (FIR) bands available in COSMOS as a function of infrared luminosity. Herschel probes rest-frame wavelengths where the bulk of the infrared radiation is emitted, allowing us to more accurately determine fundamental dust properties of our sample of infrared luminous galaxies. We find that the SED peak wavelength (λpeak) decreases and the dust mass (Mdust) increases with increasing total infrared luminosity (LIR). In the lowest infrared luminosity galaxies (log(LIR/L☉) = 10.0–11.5), we see evidence of polycyclic aromatic hydrocarbon (PAH) features (λ ∼ 7–9 μm), while in the highest infrared luminosity galaxies (LIR > 1012 L☉) we see an increasing contribution of hot dust and/or power-law emission, consistent with the presence of heating from an active galactic nucleus (AGN). We study the relationship between stellar mass and star formation rate of our sample of infrared luminous galaxies and find no evidence that Herschel-selected galaxies follow the SFR/M* "main sequence" as previously determined from studies of optically selected, star-forming galaxies. Finally, we compare the mid-infrared to FIR properties of our infrared luminous galaxies using the previously defined diagnostic, IR8 ≡ LIR/L8, and find that galaxies with LIR ≳ 1011.3 L☉ tend to systematically lie above (× 3–5) the IR8 "infrared main sequence," suggesting either suppressed PAH emission or an increasing contribution from AGN heating.
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Spitzer Space Telescope
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We present Spitzer IRS mid-infrared spectra for 15 gravitationally lensed, 24 μm-selected galaxies, and combine the results with four additional very faint galaxies with IRS spectra in the literature. The median intrinsic 24 μm flux density of the sample is 130 μJy, enabling a systematic survey of the spectral properties of the very faint 24 μm sources that dominate the number counts of Spitzer cosmological surveys. Six of the 19 galaxy spectra (32%) show the strong mid-IR continuua expected of AGNs; X-ray detections confirm the presence of AGNs in three of these cases, and reveal AGNs in two other galaxies. These results suggest that nuclear accretion may contribute more flux to faint 24 μm-selected samples than previously assumed. Almost all the spectra show some aromatic (PAH) emission features; the measured aromatic flux ratios do not show evolution from z = 0. In particular, the high signal-to-noise mid-IR spectrum of SMM J163554.2+661225 agrees remarkably well with low-redshift, lower luminosity templates. We compare the rest-frame 8 μm and total infrared luminosities of star-forming galaxies, and find that the behavior of this ratio with total IR luminosity has evolved modestly from z = 2 to z = 0. Since the high aromatic-to-continuum flux ratios in these galaxies rule out a dominant contribution by AGNs, this finding implies systematic evolution in the structure and/or metallicity of infrared sources with redshift. It also has implications for the estimates of star-forming rates inferred from 24 μm measurements, in the sense that at z ∼ 2, a given observed frame 24 μm luminosity corresponds to a lower bolometric luminosity than would be inferred from low-redshift templates of similar luminosity at the corresponding rest wavelength.
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view Abstract Citations (84) References (27) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The IRAS Bright Galaxy Sample. III. 1-10 micrometer Observations and Coadded IRAS Data for Galaxies LIR>=10E11 Lsun Carico, David P. ; Sanders, D. B. ; Soifer, B. T. ; Elias, J. H. ; Matthews, K. ; Neugebauer, G. Abstract Galaxies from the IRAS Bright Galaxy Sample with infrared luminosities L_IR_>=10^11^ L_sun_ have been measured at 1.3, 1.6, 2.2, 3.7, and 10 microns. In addition, coadded IRAS measurements at all four IRAS bands have been obtained. It is found that an increase in the total infrared luminosity above L_IR_>=10^11^ L_sun_ is correlated with increased emission from hot dust with characteristic temperatures ~800 K contributing a substantial fraction of the 2.2 and 3.7 micron emission. This hot dust emission appears to "turn on" at luminosities of roughly 10^11^ L_sun_. The far-infrared emission cannot be modeled with a single dust temperature, but requires a cold (T ~ 30-50 K) component coupled with a warmer (T >~ 70 K) component. Although the relative contribution from the cold component decreases with increasing luminosity, the temperature of the warmer component is independent of luminosity. The fnu_ (12 micron)/fnu_ (25 micron) ratios for the galaxies in this sample are small compared with other extragalactic objects, indicating that the radiation at 12 and 25 microns is dominated by emission from large dust grains radiating at high temperatures, rather than PAHs. The spatial distribution of the 10 micron emission indicates a substantial extended component for most of the galaxies in this sample, implying that star formation processes contribute significantly to the luminosities. However, one-third of the galaxies have exponential scale sizes characteristic of compact sources, and half of the galaxies have 10 micron emission consistent with a contribution of 50% or more from a central point source. Publication: The Astronomical Journal Pub Date: February 1988 DOI: 10.1086/114640 Bibcode: 1988AJ.....95..356C Keywords: Astronomical Spectroscopy; Brightness Distribution; Galactic Structure; Infrared Spectra; Radiant Flux Density; Cosmic Dust; Far Infrared Radiation; Star Formation; Temperature Distribution; Astrophysics; INFRARED: SOURCES; GALAXIES: GENERAL; RADIO SOURCES: GALAXIES full text sources ADS | data products SIMBAD (81) NED (69) Related Materials (4) Part 1: 1986BAAS...18.1035S Part 2: 1987ApJ...320..238S Part 4: 1989AJ.....98..766S Part 5: 1990AJ....100...70C
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view Abstract Citations (142) References (36) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Spectroscopy of Luminous Infrared Galaxies at 2 Microns. I. The Ultraluminous Galaxies (L IR 2pt>-11.5pt-3pt approximately 10 12 Lsun ) Goldader, Jeffrey D. ; Joseph, R. D. ; Doyon, Rene ; Sanders, D. B. Abstract We present high-quality spectra covering the K window at a resolving power of 340 for a sample of 13 ultraluminous (L_IR_ ~> 10^12^ L_sun_) infrared-selected galaxies, and line fluxes for a comparison sample of 24 lower luminosity galaxies. The 2 micron spectra of 10 of the ultraluminous galaxies are characterized by emission and absorption features commonly associated with stars and star formation; two others have the red power-law spectra and Brγ line widths of Seyfert 1 galaxies; the final galaxy has strong emission from hot dust. We have found no broad-line active nuclei not already known from optical observations, despite the fact that the extinction at 2 microns is 1/10 that at optical wavelengths; any putative Seyfert 1 nuclei must be deeply buried. Powerful continua and emission lines from H_2_ and Brγ are detected in all the ultraluminous galaxies. Comparing the H_2_ 1-0 S(1), Brγ, and 2 microns and far-infrared luminosities to those of the lower luminosity galaxies yields several major results. First, the dereddened Brγ emission, relative to the far-infrared luminosity, Is significantly depressed in the ultraluminous sample, when compared to the lower luminosity galaxies. Five of the ultraluminous galaxies have L_Brγ_/L_IR_ ratios lower than for any of the comparison objects. Second, the H_2_ 1-0 S(1) luminosity is proportional to the far-infrared luminosity, This suggests that the process producing the far-infrared luminosity is also responsible, directly or indirectly, for producing the excited H_2_, and that the H_2_ apparently comes from optically thin regions in both classes of objects. Third, eight of the 13 ultraluminous systems have lower 2 micron/far-infrared luminosity ratios than any of the lower luminosity galaxies, and five of these are the galaxies also deficient in Brγ. These three findings may be understood if the H_2_, Brγ, and 2 micron continua in the ultraluminous galaxies arise from spatially distinct regions, with the continuum and Brγ largely coming from volumes optically thick even at 2 microns, and obscured in such a fashion that the extinctions measured using optical spectroscopy do not properly measure the true optical depths. If this is the case, then even near-infrared spectroscopy may be unable to exclude the presence of undetected powerful active galactic nuclei in the ultraluminous galaxies. Publication: The Astrophysical Journal Pub Date: May 1995 DOI: 10.1086/175585 Bibcode: 1995ApJ...444...97G Keywords: Astronomical Spectroscopy; Extremely High Frequencies; Galaxies; Infrared Astronomy; Infrared Spectroscopy; Stellar Luminosity; Active Galactic Nuclei; Emission Spectra; Far Infrared Radiation; Hydrogen; Star Formation; Starburst Galaxies; Astronomy; GALAXIES: ACTIVE; GALAXIES: STARBURST; INFRARED: GALAXIES full text sources ADS | data products SIMBAD (37) NED (37) Related Materials (2) Part 2: 1997ApJS..108..449G Part 3: 1997ApJ...474..104G
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The far-infrared (10–100 μm) spectra of galaxies detected in all four wavelength bands by IRAS are modelled in terms of three components: a cool 'disc' component; a warmer 'starburst' component, and a 'Seyfert' component peaking at 25 μm. The luminosity in the 'disc' component is well-correlated with the optical luminosity of the galaxy and this component is interpreted as emission from interstellar dust illuminated by the galaxy's starlight. The 'starburst' component is interpreted as being due to a burst of star formation in the galaxy nucleus and its spectrum is fitted well by a model consisting of hot stars embedded in an optically thick dust cloud. The 'Seyfert' component is interpreted as being due to a power-law continuum source within a dust cloud presumably associated with the narrow-line region of the compact source. The density distribution in this dust cloud behaves as |$n(r)\propto r^{-1}$|. The luminosity in the 'starburst' component is correlated with Hubble type and whether or not the galaxy has a bar. The luminosity in the 'Seyfert' component is correlated with the X-ray luminosity of the galaxy, supporting the hypothesis that the central compact power-law continuum source is responsible for illuminating the dust seen emitting in the far-infrared. Detailed ultraviolet to submillimetre spectra of several galaxies are compared with the predictions of the models. For the non-Seyfert and many of the Seyferts the proposed models are a good fit, but for NGC 1068 and several other Seyfert galaxies a more complex geometry for the dust distribution is indicated. The observed 1–10 μm spectra can be fitted in several cases with a higher-optical-depth 'Seyfert' component, but since a power-law continuum is seen in the ultraviolet for many of these Seyferts, we infer that the dust in the narrow-line region has a non-spherically symmetric geometry, for example being concentrated into clouds. For Arp 220 and NGC 4418, 'starburst' models with additional internal or interstellar extinction give a good fit, though a deeply dust-embedded quasar is also a possibility for Arp 220.
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We present 7–180 μm photometry of a sample of hyperluminous infrared galaxies (HyLIGs) obtained with the photometer and camera mounted on the Infrared Space Observatory. We have used radiative transfer models of obscured starbursts and dusty torii to model their spectral energy distributions (SEDs). We find that IRAS F00235+1024, IRAS F14218+3845 and IRAS F15307+3252 require a combination of starburst and active galactic nuclei (AGN) components to explain their mid- to far-infrared (FIR) emission, while for TXS 0052+471 a dust torus AGN model alone is sufficient. For IRAS F00235+1024 and IRAS F14218+3845 the starburst component is the predominant contributor, whereas for IRAS F15307+3252 the dust torus component dominates. The implied star formation rates (SFRs) for these three sources estimated from their infrared luminosities are yr−1h50−2 and are amongst the highest SFRs estimated to date. We also demonstrate that the well-known radio–FIR correlation extends into both higher radio and infrared power than previously investigated. The relation for HyLIGs has a mean q value of 1.94. The results of this study imply that better sampling of the infrared spectral energy distributions of HyLIGs may reveal that both AGN and starburst components are required to explain all the emission from the near-infrared to the submillimetre.
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