[ITAL]K[/ITAL]-Band Spectroscopy of Ultraluminous Infrared Galaxies: The 2 J[CLC]y[/CLC] Sample

Murphy, Thomas W.; Soifer, B. T.; Matthews, K.; Armus, L.; Kiger, James

doi:10.1086/318031

Cited by 47 publications

(46 citation statements)

References 32 publications

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“…The highest extinctions are usually being measured in the nuclear regions, whose values cover a broad range of A V between 0.4 and 7.7 mag, 69% of the nuclei having A V > 2.0 mag. These high extinction values are similar to those measured in the Paα emitting regions of LIRGs, whose average extinctions are found to be A V = 3-6 mag (Alonso-Herrero et al 2006) but lower than the values derived for ULIRGs using the near-IR Paα/Brγ line ratio, where visual extinctions (A V ) in excess of 10 magnitudes are relatively common in ULIRGs (Murphy et al 2001). Both optical and near-IR extinction values are also systematically lower than the Spitzer mid-IR based ones derived for local ULIRGs, which are found to be <20-30 mag for PAHemitting normal starbursts, and 30 mag for centrally concentrated energy sources with no PAH emission (Imanishi et al 2007).…”

Section: Resultssupporting

confidence: 84%

Integral field optical spectroscopy of a representative sample of ULIRGs

García-Marín

Colina²,

Arribas³

2009

A&A

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Context. Ultraluminous infrared galaxies are merging systems characterized for containing large amounts of dust and emitting the bulk of their energy in the infrared. Dust affects several of the observed properties derived from optical and near-IR rest-frame data, such as the stellar morphology and the ionized gas distribution. Systematic analysis of the dust distribution in representative samples of ULIRGs are needed to investigate its two-dimensional structure, and to establish its impact in the derivation of fundamental properties such as star formation rates, effective radii, and dynamical masses. Aims. We investigate the two-dimensional kpc-scale structure of the extinction in a representative sample of local ULIRGs using the Hα/Hβ line ratio. Methods. We use optical integral field spectroscopy obtained with the INTEGRAL instrument at the William Herschel Telescope. Complementary optical and near-IR high angular resolution HST images have also been used. Compared to classical optical long-slit analysis, our data provides information about the entire system, and not only in pre-selected orientations. Results. The extinction exhibits a very complex and patchy structure in ULIRGs on kpc scales, from basically transparent regions to others deeply embedded in dust (A V 0.0 to A V 8.0 mag). Nuclear extinction covers a broad range in A V from 0.4 to 7.7 mag , 69% of the nuclei having A V ≥ 2.0 mag. Extinction in the external regions is substantially lower than in the nuclei with 60% of the ULIRGs in the sample having median A V of less than 2 mag for the entire galaxy. While post-coalescence nuclei tend to cluster around A V values of 2 to 3 mag, pre-coalescence nuclei appear more homogeneously distributed over the entire 0.4 mag ≤A V ≤ 7.7 mag range. For the average extinction (A V 2.0) derived for the ULIRGs of the sample, the ratio of the de-reddened to observed SFR values is 6. The extinction-corrected, Hα-based SFR ranges from 10 to 300 M yr −1 . For only 27% of the cases the de-reddened SFR is <20 M yr −1 , whereas for the observed SFR this percentage increases to 87%. The IR-based SFR is always higher than the opticalbased one, with differences ranging from about 2 to up to 30. The nuclear observed SFR has an average contribution to the total one of 16% for the entire sample. Once corrected for extinction, the average value becomes 31%. Because of mostly extinction effects, the optical (I-band) half-light radius in the sample galaxies is on average a factor 2.3 larger than the corresponding near-IR (H-band) value.

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Section: Resultssupporting

confidence: 84%

Integral field optical spectroscopy of a representative sample of ULIRGs

García-Marín

Colina²,

Arribas³

2009

A&A

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“…At redshift z = 1, the IRAC 3.6 and 4.5 μm limits are a factor of 2-3 below the 3C273 SED, which implies an extinction of 0.8-1.1 mag would be required for this source to be undetected in the IRAC channels. This level of extinction is seen in some extreme ULIRGs (e.g., Genzel et al 1998;Murphy et al 2001), but this source is not luminous in the infrared. This source therefore lies at redshift z 1.…”

Section: S415mentioning

confidence: 81%

EVIDENCE FOR INFRARED-FAINT RADIO SOURCES ASz> 1 RADIO-LOUD ACTIVE GALACTIC NUCLEI

Huynh¹,

Norris²,

Siana³

et al. 2010

ApJ

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Infrared-Faint Radio Sources (IFRSs) are a class of radio objects found in the Australia Telescope Large Area Survey which have no observable mid-infrared counterpart in the Spitzer Wide-area Infrared Extragalactic (SWIRE) survey. The extended Chandra Deep Field South now has even deeper Spitzer imaging (3.6-70 μm) from a number of Legacy surveys. We report the detections of two IFRS sources in IRAC images. The nondetection of two other IFRSs allows us to constrain the source type. Detailed modeling of the spectral energy distribution of these objects shows that they are consistent with high-redshift (z 1) active galactic nuclei.

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“…Many studies have been devoted to the quantification of the relative contributions of AGN and starburst (SB), but they are hindered by the large and uncertain extinction that, usually, is not negligible even at NIR wavelengths (Goldader et al 1995;Silva et al 1998;Murphy et al 2001;Valdés et al 2005).…”

Section: Introductionmentioning

confidence: 99%

Modelling the spectral energy distribution of ULIRGs

Vega

Clemens²,

Bressan

et al. 2008

A&A

103

131

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Aims. By using the spectral energy distribution (SED) from the near-infrared to the radio of a statistically significant number of luminous infrared galaxies we determine important physical parameters for this population of objects. In particular we constrain the optical depth towards the luminosity source, the star formation rate, the star formation efficiency and the AGN fraction. Methods. We fit the near-infrared to radio spectral energy distributions of a sample of 30 luminous and ultra-luminous infrared galaxies with pure starburst models or models that include both starburst and AGN components. Results. We find that although about half of our sample have best-fit models that include an AGN component, only 30% (9/30) have an AGN that accounts for more than 10% of the infrared luminosity from 8 to 1000 μm, whereas all have an energetically dominant starburst. Our derived AGN fractions are generally in good agreement with measurements of the mid-infrared line ratios, Ne[V]/Ne [II] and O[IV]/Ne[II] by Spitzer IRS, but much lower than those derived from PAH equivalent widths or the mid-infrared spectral slope. Our models determine the mass of dense molecular gas within which active star formation takes place via the extinction required to reproduce the infrared part of the SED. Assuming that this mass is that traced by the HCN molecule, we reproduce the observed linear relation between HCN flux and infrared luminosity found previously. We also find that the star formation efficiency, as defined by the current star formation rate per unit molecular gas mass, falls as the starburst ages. Conclusions. If the evolution of ULIRGs includes a phase in which an AGN contributes an important fraction to the infrared luminosity, this phase should last an order of magnitude less time than the starburst phase. However, we find no convincing evidence that an energetically important AGN is associated with a particular phase of the starburst. Because the mass of dense molecular gas that we derive is consistent with observations of the HCN molecule, it should be possible to estimate the mass of dense, star-forming molecular gas in such objects when molecular line data are not available.

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[ITAL]K[/ITAL]-Band Spectroscopy of Ultraluminous Infrared Galaxies: The 2 J[CLC]y[/CLC] Sample

Cited by 47 publications

References 32 publications

Integral field optical spectroscopy of a representative sample of ULIRGs

Integral field optical spectroscopy of a representative sample of ULIRGs

EVIDENCE FOR INFRARED-FAINT RADIO SOURCES ASz> 1 RADIO-LOUD ACTIVE GALACTIC NUCLEI

Modelling the spectral energy distribution of ULIRGs

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