Exploring the physical properties of local star-forming ULIRGs from the ultraviolet to the infrared

Abstract

We apply the da Cunha et al. (2008, MNRAS, 388, 1595 model of the spectral energy distribution (SEDs) of galaxies to a small pilot sample of purely star-forming ultra-luminous infrared galaxies (ULIRGs). We interpret the observed SEDs of 16 ULIRGs using this physically-motivated model that accounts for both the emission of stellar populations from the ultraviolet to the near-infrared and for the attenuation by dust in two components: an optically-thick starburst component and the diffuse ISM. The infrared emission is computed by assuming that all the energy absorbed by dust in these components is re-radiated at mid-and far-infrared wavelengths. This model allows us to derive statistically physical properties including star formation rates, stellar masses, the temperatures and masses of different dust components, and plausible star formation histories. We find that, although the ultraviolet-to-near-infrared emission represents only a small fraction of the total power radiated by ULIRGs, observations in this wavelength range are important for understanding the properties of the stellar populations and dust attenuation in the diffuse ISM of these galaxies. Furthermore, our analysis indicates that the use of mid-infrared spectroscopy from the infrared spectrograph on the Spitzer Space Telescope is crucial to obtain realistic estimates of the extinction to the central energy source, mainly via the depth of the 9.7-μm silicate feature, and thus accurately constrain the total energy balance. Our findings are consistent with the notion that, in the local Universe, the physical properties of ULIRGs are fundamentally different from those of galaxies with lower infrared luminosities and that local ULIRGs are the result of merger-induced starbursts. While these are well-established ideas, we demonstrate the usefulness of our SED modelling in deriving relevant physical parameters that provide clues to the star formation mode of galaxies.

Galaxy evolution and star formation efficiency at 0.2 < z < 0.6

“…Stellar masses were found between 10 10 and 10 12 M or somewhat higher in the case of quasars. Figure 10 displays the star formation rate, derived from the infrared luminosity, versus the stellar mass, in comparison to the ULIRG samples of Da Cunha et al (2010) and Fiolet et al (2009). Our sample points follow the general trend, with the bias of strong SFR, due to our selection on L(FIR).…”

CO excitation of normal star-forming galaxies out toz= 1.5 as regulated by the properties of their interstellar medium

“…We use here and in the following only objects for which U could be measured, which limits the sample to six objects in total. For the (U)LIRGs we used the average U value of 35 from Magdis et al (2012) and da Cunha et al (2010) because individual measurements are available for only three galaxies ( U = 32.5, 24.6 and 52.8 for IRAS10565, IRAS17208 and IRAS12112, returning an average that is also very close to the adopted value for this smaller subsample). To estimate typical values for the SFE, we adopted the values reported in Sargent et al (2014).…”

Herschel-ATLAS: the connection between star formation and AGN activity in radio-loud and radio-quiet active galaxies

“…Far-IR luminosity is widely used to measure star formation activity. As discussed by Hardcastle et al (2013) neither the integrated far-IR luminosity nor the 250-µm luminosity is a completely reliable estimator of SFR because of the contribution by cold dust heated by old stellar populations (da Cunha et al 2010;Smith et al 2012). However, we are secure using them as long as the far-IR emission is dominated by warm dust heated by star formation which, gives rise to dust temperatures ∼25 K or more.…”