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. But old
stellar populations may hide in our VYGs despite our conservative VYG
sample built with galaxies that are globally bluer than within the
region viewed by the SDSS fibre. The VYG fractions versus mass decrease
more gradually compared to the Tweed et al. predictions using analytical
and semi-analytical models of galaxy formation, but agree better with
the SIMBA hydrodynamical simulation. These discrepancies highlight the
usefulness of VYGs in constraining the strong uncertainties in both
galaxy formation models and spectral modelling of galaxy SFHs. Given the
lognormal cosmic SFH, these mean VYG fractions suggest that galaxies
above 108M⊙ undergo at most four major starbursts on average.
Original language | English |
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Pages (from-to) | 1791-1811 |
Number of pages | 21 |
Journal | Monthly Notices of the Royal Astronomical Society |
Volume | 492 |
Issue number | 2 |
Early online date | 19 Dec 2019 |
DOIs | |
Publication status | Published - 1 Feb 2020 |
Keywords / Materials (for Non-textual outputs)
- astro-ph.GA