Browsing by Author "Hurley, P."
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- The Complex Physics of Dusty Star-Forming Galaxies at High Redshifts as Revealed by Herschel and SpitzerLo Faro, B.; Franceschini, A.; Vaccari, M.; Silva, L.; Rodighiero, G.; Berta, S.; Bock, J.; Burgarella, D.; Buat, V.; Cava, A.; Clements, D. L.; Cooray, A.; Farrah, D.; Feltre, A.; Solares, E. A. G.; Hurley, P.; Lutz, D.; Magdis, G. E.; Magnelli, B.; Marchetti, L.; Oliver, S. J.; Page, M. J.; Popesso, P.; Pozzi, F.; Rigopoulou, D.; Rowan-Robinson, M.; Roseboom, I. G.; Scott, D.; Smith, A. J.; Symeonidis, M.; Wang, L.; Wuyts, S. (IOP Publishing Ltd., 2013-01)We combine far-infrared photometry from Herschel (PEP/HerMES) with deep mid-infrared spectroscopy from Spitzer to investigate the nature and the mass assembly history of a sample of 31 luminous and ultraluminous infrared galaxies ((U)LIRGs) at z similar to 1 and 2 selected in GOODS-S with 24 mu m fluxes between 0.2 and 0.5 mJy. We model the data with a self-consistent physical model (GRASIL) which includes a state-of-the-art treatment of dust extinction and reprocessing. We find that all of our galaxies appear to require massive populations of old (>1 Gyr) stars and, at the same time, to host a moderate ongoing activity of star formation (SFR <= 100 M-circle dot yr(-1)). The bulk of the stars appear to have been formed a few Gyr before the observation in essentially all cases. Only five galaxies of the sample require a recent starburst superimposed on a quiescent star formation history. We also find discrepancies between our results and those based on optical-only spectral energy distribution (SED) fitting for the same objects; by fitting their observed SEDs with our physical model we find higher extinctions (by Delta A(V) similar to 0.81 and 1.14) and higher stellar masses (by Delta log(M-*) similar to 0.16 and 0.36 dex) for z similar to 1 and z similar to 2 (U)LIRGs, respectively. The stellar mass difference is larger for the most dust-obscured objects. We also find lower SFRs than those computed from LIR using the Kennicutt relation due to the significant contribution to the dust heating by intermediate-age stellar populations through "cirrus" emission (similar to 73% and similar to 66% of the total L-IR for z similar to 1 and z similar to 2 (U)LIRGs, respectively).
- Far-infrared fine-structure line diagnostics of ultraluminous infrared galaxiesFarrah, D.; Lebouteiller, V.; Spoon, H. W. W.; Bernard-Salas, J.; Pearson, C.; Rigopoulou, D.; Smith, H. A.; Gonzalez-Alfonso, E.; Clements, D. L.; Efstathiou, A.; Cormier, D.; Afonso, J.; Petty, S. M.; Harris, K.; Hurley, P.; Borys, C.; Verma, A.; Cooray, A.; Salvatelli, V. (IOP Publishing Ltd., 2013-10)We present Herschel observations of 6 fine-structure lines in 25 ultraluminous infrared galaxies at z < 0.27. The lines, [O III]52 mu m, [N III] 57 mu m, [O I]63 mu m, [N II]122 mu m, [O I]145 mu m, and [C II]158 mu m, are mostly single Gaussians with widths < 600 km s(-1) and luminosities of 10(7)-10(9) L-circle dot. There are deficits in the [O I] 63/L-IR, [N II]/L-IR, [O I]145/L-IR, and [C II]/L-IR ratios compared to lower luminosity systems. The majority of the line deficits are consistent with dustier H II regions, but part of the [C II] deficit may arise from an additional mechanism, plausibly charged dust grains. This is consistent with some of the [C II] originating from photodissociation regions or the interstellar medium (ISM). We derive relations between far-IR line luminosities and both the IR luminosity and star formation rate. We find that [N II] and both [O I] lines are good tracers of the IR luminosity and star formation rate. In contrast, [C II] is a poor tracer of the IR luminosity and star formation rate, and does not improve as a tracer of either quantity if the [C II] deficit is accounted for. The continuum luminosity densities also correlate with the IR luminosity and star formation rate. We derive ranges for the gas density and ultraviolet radiation intensity of 10(1) < n < 10(2.5) and 10(2.2) < G(0) < 10(3.6), respectively. These ranges depend on optical type, the importance of star formation, and merger stage. We do not find relationships between far-IR line properties and several other parameters: active galactic nucleus (AGN) activity, merger stage, mid-IR excitation, and SMBH mass. We conclude that these far-IR lines arise from gas heated by starlight, and that they are not strongly influenced by AGN activity.
- Mid- to far-infrared properties of star-forming galaxies and active galactic nucleiMagdis, G. E.; Rigopoulou, D.; Helou, G.; Farrah, D.; Hurley, P.; Alonso-Herrero, A.; Bock, J.; Burgarella, D.; Chapman, S.; Charmandaris, V.; Cooray, A.; Dai, Y. S.; Dale, D.; Elbaz, D.; Feltre, A.; Hatziminaoglou, E.; Huang, J. S.; Morrison, G.; Oliver, S.; Page, M.; Scott, D.; Shi, Y. (EDP SCIENCES, 2013-10)We study the mid- to far-IR properties of a 24 mu m-selected flux-limited sample (S-24 > 5mJy) of 154 intermediate redshift (< z > similar to 0.15), infrared luminous galaxies, drawn from the 5 Milli-Jansky Unbiased Spitzer Extragalactic Survey. By combining existing mid-IR spectroscopy and new Herschel SPIRE submm photometry from the Herschel Multi-tiered Extragalactic Survey, we derived robust total infrared luminosity (L-IR) and dust mass (M-dust) estimates and infered the relative contribution of the AGN to the infrared energy budget of the sources. We found that the total (8-1000 mu m) infrared emission of galaxies with weak 6.2 mu m PAH emission (EW6.2 <= 0.2 mu m) is dominated by AGN activity, while for galaxies with EW6.2 > 0.2 mu m more than 50% of the L-IR arises from star formation. We also found that for galaxies detected in the 250-500 mu m Herschel bands an AGN has a statistically insignificant effect on the temperature of the cold dust and the far-IR colours of the host galaxy, which are primarily shaped by star formation activity. For star-forming galaxies we reveal an anti-correlation between the L-IR-to-rest-frame 8 mu m luminosity ratio, IR8 = L-IR/L-8 and the strength of PAH features. We found that this anti-correlation is primarily driven by variations in the PAHs emission, and not by variations in the 5-15 mu m mid-IR continuum emission. Using the [NeIII]/[NeII] line ratio as a tracer of the hardness of the radiation field, we confirm that galaxies with harder radiation fields tend to exhibit weaker PAH features, and found that they have higher IR8 values and higher dust-mass-weighted luminosities (L-IR/M-dust), the latter being a proxy for the dust temperature (T-d). We argue that these trends originate either from variations in the environment of the star-forming regions or are caused by variations in the age of the starburst. Finally, we provide scaling relations that will allow estimating L-IR, based on single-band observations with the mid-infrared instrument, on board the upcoming James Webb Space Telescope.