Compact Galaxies with Active Star Formation from the SDSS DR14: Star-Formation Rates Derived from Combinations of Luminosities in Different Wavelength Ranges

Abstract

Physical characteristics of a large sample of compact galaxies with active star formation from the SDSS DR14 are derived. The sample includes approximately 30 000 compact isolated galaxies with angular diameters <6″. The emission lines Hβ with equivalent widths EW(Hβ) ≥ 1 nm are observed in the spectra of selected galaxies. The stellar masses of compact galaxies are distributed in a wide range from 105M⊙ to 1011M⊙ with a maximum at ~109M⊙. The oxygen abundances for the bulk of compact galaxies are distributed in the range 7.8…8.2 with a maximum at ~8.05. Compact galaxies are characterized with high specific star-formation rates of 10…100 Gyr–1. The SDSS spectroscopic data were supplemented by photometric data in the far- and near-ultraviolet ranges from the GALEX and in the mid-infrared range at 22 μm from the WISE all-sky surveys. The star-formation rate, concisely named “composite” one, was determined using combinations of two out of five observed luminosities: luminosity L(Hα) in the emission line Hα, monochromatic luminosities in the ultraviolet continuum L(FUV), and L(NUV) and in the mid-infrared continuum L(22 μm) as well as the total luminosities in the infrared range L(TIR). “Composite” star formation rates in compact galaxies with active star formation are compared with those determined from the extinction- and spectral aperture-corrected luminosities of galaxies in the hydrogen emission line Hβ. Relations for “composite” star formation rates with different combinations of indicators were obtained, which are mutually consistent and correspond to star-formation rates SFR(Hβ) derived from the luminosities of galaxies in the hydrogen emission line Hβ, corrected for extinction and spectral aperture.