GALEX-SDSS-WISE Legacy Catalog (GSWLC): Star Formation Rates, Stellar Masses and Dust Attenuations of 700,000 Low-redshift Galaxies (1610.00712v1)

Abstract: In this paper, we present GALEX-SDSS-WISE Legacy Catalog (GSWLC), a catalog of physical properties (stellar masses, dust attenuations and star formation rates (SFRs)) of ~700,000 galaxies with SDSS redshifts below 0.3. GSWLC contains galaxies within the GALEX footprint, regardless of a UV detection, covering 90% of SDSS. The physical properties were obtained from UV/optical SED fitting following Bayesian methodology of Salim et al. (2007), with improvements such as blending corrections for low-resolution UV photometry, flexible dust attenuation laws, and emission line corrections. GSWLC includes mid-IR SFRs derived from IR templates based upon 22 micron WISE observations. These estimates are independent of UV/optical SED fitting, in order to separate possible systematics. The paper argues that the comparison of specific SFRs (SSFRs) is more informative and physically motivated than the comparison of SFRs. SSFRs resulting from the UV/optical SED fitting are compared to the mid-IR SSFRs, and to SSFRs from three published catalogs. For "main sequence" galaxies with no AGN contribution all SSFRs are in very good agreement (within 0.1 dex on average). In particular, the widely-used aperture-corrected SFRs from MPA/JHU catalog show no systematic offsets, in contrast to some integral-field spectroscopy results. For galaxies below the main sequence (log SSFR<-11), mid-IR (S)SFRs based on fixed luminosity-SFR conversion are severely biased (up to 2 dex) because the dust is primarily heated by old stars. Furthermore, mid-IR (S)SFRs are overestimated by up to 0.6 dex for galaxies with AGN, presumably due to non-stellar dust heating. UV/optical (S)SFRs are thus preferred to IR-based (S)SFRs for quenched galaxies and those which host AGN.

• The paper introduces a refined Bayesian UV/optical SED fitting method to analyze star formation, stellar mass, and dust attenuation in 700,000 low-redshift galaxies.
• It validates SFR estimates by comparing UV/optical and independent mid-IR measurements, achieving a typical alignment within 0.1 dex for main sequence galaxies.
• The catalog minimizes systematic biases and provides a robust dataset for exploring galaxy evolution and the interplay between star formation and stellar mass.

Overview of the GALEX--SDSS--WISE Legacy Catalog (GSWLC)

The GALEX--SDSS--WISE Legacy Catalog (GSWLC) offers a comprehensive dataset that quantifies physical properties, including star formation rates (SFRs), stellar masses, and dust attenuations, for approximately 700,000 low-redshift galaxies. These galaxies are selected based on redshifts from the Sloan Digital Sky Survey (SDSS) below 0.3 and are further analyzed using data from the GALEX and WISE missions. This catalog covers a substantial 90% of the SDSS footprint, ensuring a representative survey of the local universe.

Methodology and Improvements

The GSWLC employs UV/optical Spectral Energy Distribution (SED) fitting using a Bayesian framework, significantly improving earlier methodologies. The process integrates various corrective measures such as accounting for blending in low-resolution UV photometry and incorporating flexible dust attenuation laws. An essential enhancement is the comparison of SED-based SFRs with those derived from mid-infrared data based on WISE 22 μm observations. These IR-based SFRs are calculated independently to mitigate systematic biases.

Examining SFRs in terms of specific star formation rates (SSFRs), which normalize star formation by stellar mass, provides more physically meaningful insights into galaxy evolution. This approach highlights the agreement between SED and mid-IR SSFRs, especially for "main sequence" galaxies absent Active Galactic Nucleus (AGN) activity, with a typical deviation of only 0.1 dex. Notably, the catalog identifies that mid-IR SSFRs can be severely distorted for passive galaxies or those with AGN due to non-stellar contributions to dust heating, encouraging the preference for UV/optical SED-based measures in such cases.

Systematics, Comparisons, and Implications

The paper's rigorous methodology ensures minimal internal and external systematics, validated by comparisons against alternative SFR estimates from emission lines and integral-field spectroscopy. The GSWLC's robust dataset allows detailed exploration of star formation across a large galaxy sample and serves as a critical tool for studying galaxy evolution in the low-redshift universe.

Stellar masses derived from the optical data show slight but consistent deviations in specific scenarios, particularly in galaxies hosting significant recent star formation. These masses tend to be moderately higher than those reported in earlier catalogs, attributed to the flexibility of assumed SF histories in the modeling.

Future Directions and Utility

The GSWLC is expected to facilitate substantial advances in understanding galaxy formation and the interplay between stellar mass growth and star-forming activities within different galactic environments. Its large scale and diverse datasets enable both detailed individual galaxy studies and the exploration of broader statistical properties, supporting further theoretical developments in astrophysical models.

In essence, the GSWLC catalog provides a significant resource for the astrophysics community, offering enhanced insights into the star formation processes and galactic evolution at low redshifts through refined data interpretation and robust cross-comparisons with independent methodologies.