Abstract
We complement our previous analysis of a sample of z~1-2 luminous and ultra-luminous infrared galaxies ((U)LIRGs), by adding deep VLA radio observations at 1.4 GHz to a large data-set from the far-UV to the sub-mm, including Spitzer and Herschel data. Given the relatively small number of (U)LIRGs in our sample with high S/N radio data, and to extend our study to a different family of galaxies, we also include 6 well sampled near IR-selected BzK galaxies at z~1.5. From our analysis based on the radiative transfer spectral synthesis code GRASIL, we find that, while the IR luminosity may be a biased tracer of the star formation rate (SFR) depending on the age of stars dominating the dust heating, the inclusion of the radio flux offers significantly tighter constraints on SFR. Our predicted SFRs are in good agreement with the estimates based on rest-frame radio luminosity and the Bell (2003) calibration. The extensive spectro-photometric coverage of our sample allows us to set important constraints on the SF history of individual objects. For essentially all galaxies we find evidence for a rather continuous SFR and a peak epoch of SF preceding that of the observation by a few Gyrs. This seems to correspond to a formation redshift of z~5-6. We finally show that our physical analysis may affect the interpretation of the SFR-M* diagram, by possibly shifting, with respect to previous works, the position of the most dust obscured objects to higher M* and lower SFRs.
Highlights
In star-forming galaxies, stars, gas and dust are mixed in a very complicated way, and dust obscuration strongly depends on their relative geometrical distribution
In BLF13 we have shown that, due to the significant contribution of cirrus emission to the total LIR whose heating source includes already evolved stellar populations (ages older than the typical timescale for young stars to escape from the parent molecular clouds (MCs), typically ranging between ∼ 3 Myr and ∼ 90 Myr), our inferred SFR10 are systematically lower than those based on the K98 calibration, by a factor ∼ 2-2.5
In this paper we have extended the thorough spectral energy distribution (SED) analysis performed by BLF13, by including the modelling of radio emission for a sample of high-z (U)LIRGs and BzK-selected galaxies for which a full multiwavelength dataset from far-UV to sub-mm was already available
Summary
In star-forming galaxies, stars, gas and dust are mixed in a very complicated way, and dust obscuration strongly depends on their relative geometrical distribution. This work is intended to be complementary to the physical analysis performed in our previous paper (BLF13) and aimed at testing BLF13 estimates, in particular those concerning M and SF R, against observations through the investigation of the radio emission of high-z star forming galaxies For this reason we first apply our analysis to the same sample of 31 high-z (U)LIRGs whose far-UV to sub-mm properties have been deeply investigated in BLF13 and in order to strengthen our conclusions, we extend the analysis by including a small but well representative sample of 6 BzKselected star forming main sequence (MS) galaxies at z∼1.5 for which high S/N radio observations are available. All the objects which were classified by F10 as AGN-dominated, on the basis of several indicators such as broad and high ionization lines in optical spectra, lack of a 1.6 μm stellar bump in the SED, X-ray bright sources, low mid-IR 6.2 μm EW
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