Star-formation histories of local luminous infrared galaxies

Abstract

We present analysis of the integrated spectral energy distribution (SED) from the ultraviolet (UV) to the far-infrared and H alpha of a sample of 29 local systems and individual galaxies with infrared (IR) luminosities between 10^11 L_⨀and 10^11.8 L_⨀. We combined new narrow-band Hα + [NII] and broad-band g, r optical imaging taken with the Nordic Optical Telescope (NOT), with archival GALEX, 2MASS, Spitzer, and Herschel data. Their SEDs (photometry and integrated Hα flux) were fitted simultaneously with a modified version of the MAGPHYS code using stellar population synthesis models for the UV-near-IR range and thermal emission models for the IR emission taking the energy balance between the absorbed and re-emitted radiation into account. From the SED fits, we derive the star-formation histories (SFH) of these galaxies. For nearly half of them, the star-formation rate appears to be approximately constant during the last few Gyr. In the other half, the current star-formation rate seems to be enhanced by a factor of 3-20 with respect to what occurred ∼1 Gyr ago. Objects with constant SFH tend to be more massive than starbursts, and they are compatible with the expected properties of a main-sequence (M-S) galaxy. Likewise, the derived SFHs show that all our objects were M-S galaxies ∼1 Gyr ago with stellar masses between 10^10.1 and 10^11.5 M_⨀. We also derived the average extinction (A_v = 0.6-3 mag) and the polycyclic aromatic hydrocarbon luminosity to L_IR ratio (0.03-0.16) from our fits. We combined the A_v with the total IR and Hα luminosities into a diagram that can be used to identify objects with rapidly changing (increasing or decreasing) SFR during the past 100 Myr.