The frequency of very young galaxies in the local Universe – II. The view from SDSS spectra

Abstract

Only a handful of galaxies in the local Universe appear to be very young. We estimate the fraction of very young galaxies (VYGs), defined as those with more than half their stellar masses formed within the last Gyr. We fit non-parametric star formation histories (SFHs) to ∼280 000 galaxy spectra from a flux- and volume-limited subsample of the Main Galaxy Sample (MGS) of the SDSS, which is also complete in mass-to-light ratio, thus properly accounting for passive galaxies of a given mass. The VYG fractions decrease with increasing galaxy stellar mass, from ∼50 per cent at m=108M⊙ to ∼0.1 per cent at m=1011.5M⊙⁠, with differences of up to 1 dex between the different spectral models used to estimate the SFH and on how we treat aperture effects.