We derive a variety of physical parameters including star formation rates (SFRs), dust attenuation, and burst mass fractions for 6472 galaxies observed by the Galaxy Evolution Explorer (GALEX) and present in the Sloan Digital Sky Survey Data Release 1 (SDSS DR1) main spectroscopic sample. Parameters are estimated in a statistical way by comparing each observed broadband spectral energy distribution (SED) (two GALEX and five SDSS bands) with an extensive library of model galaxy SEDs, which cover a wide range of star formation histories and include stochastic starbursts. We compare the constraints derived using SDSS bands only with those derived using the combination of SDSS and GALEX photometry. We find that the addition of the GALEX bands leads to significant improvement in the estimation of both the dust optical depth and the star formation rate over timescales of 100 Myr to 1 Gyr in a galaxy. We attain sensitivity to SFRs as low as 10-3 M⊙ yr -1, and we find that low levels of star formation (SF) are mostly associated with early-type, red galaxies. The least massive galaxies have ratios of current to past-averaged SF rates (b-parameter) consistent with constant SF over a Hubble time. For late-type galaxies, this ratio on average decreases with mass. We find that b correlates tightly with NUV - r color, implying that the SF history of a galaxy can be constrained on the basis of the NUV - r color alone. The fraction of galaxies that have undergone a significant starburst episode within the last 1 Gyr steeply declines with mass, from ∼20% for galaxies with ∼108 M⊙ to ∼5% for ∼1011 M⊙ galaxies.
Bibliographical noteFunding Information:
We thank Sukyoung Yi for comments. S. S. thanks Andrew Gould. S. C. thanks the Alexander von Humboldt Foundation. GALEX is a NASA Small Explorer, launched in 2003 April. We gratefully acknowledge NASA’s support for construction, operation, and science analysis for the GALEX mission, developed in cooperation with the CNES of France and the Korean Ministry of Science and Technology. Funding for the creation and distribution of the SDSS Archive has been provided by the Alfred P. Sloan Foundation, the participating institutions, NASA, the NSF, DoE, Monbukagakusho, and the Max Planck Society.
All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Space and Planetary Science