Stellar Masses and SFRs for 1M Galaxies from SDSS and WISE

TL;DR

This study combines SDSS and WISE data for over 850,000 galaxies to model their spectral energy distributions, deriving new mid-infrared star formation rate calibrations and revealing the bi-modality of galaxy star formation activity.

Contribution

It provides the first comprehensive mid-IR-based analysis of galaxy star formation rates and the bi-modality in star formation activity using a large, combined photometric dataset.

Findings

New mid-IR SFR calibrations for galaxies.

Confirmation of the star formation bi-modality with a main sequence slope of 0.80.

Most stars in the universe form in luminous galaxies around the green valley.

Abstract

We combine SDSS and WISE photometry for the full SDSS spectroscopic galaxy sample, creating SEDs that cover lambda=0.4-22 micron for an unprecedented large and comprehensive sample of 858,365 present-epoch galaxies. Using MAGPHYS we then model simultaneously and consistently both the attenuated stellar SED and the dust emission at 12 micron and 22 micron, producing robust new calibrations for monochromatic mid-IR star formation rate proxies. These modeling results provide the first mid-IR-based view of the bi-modality in star formation activity among galaxies, exhibiting the sequence of star-forming galaxies (main sequence) with a slope of dlogSFR/dlogM*=0.80 and a scatter of 0.39 dex. We find that these new star-formation rates along the SF main sequence are systematically lower by a factor of 1.4 than those derived from optical spectroscopy. We show that for most present-day galaxies the 0.4-22 micron SED fits can exquisitely predict the fluxes measured by Herschel at much longer wavelengths. Our analysis also illustrates that the majorities of stars in the present-day universe is formed in luminous galaxies (~L*) in and around the green valley of the color-luminosity plane. We make the matched photometry catalog and SED modeling results publicly available.