Lyman break and ultraviolet-selected galaxies at z ˜ 1 - I. Stellar populations from the ALHAMBRA survey

We take advantage of the exceptional photometric coverage provided by
the combination of GALEX data in the ultraviolet (UV) and the ALHAMBRA
survey in the optical and near-infrared to analyse the physical
properties of a sample of 1225 GALEX-selected Lyman break galaxies
(LBGs) at 0.8 ≲ z ≲ 1.2 that are located in the COSMOS field.
This is the largest sample of LBGs studied in this redshift range to
date. According to a spectral energy distribution (SED) fitting with
synthetic stellar population templates, we find that LBGs at z ˜ 1
are mostly young galaxies with a median age of 341 Myr and have
intermediate dust attenuation, <E<SUB>s</SUB>(B – V)> ˜
0.20. Owing to the selection criterion, LBGs at z ˜ 1 are
UV-bright galaxies and have a high dust-corrected total star formation
rate (SFR), with a median value of 16.9 M<SUB>⊙</SUB>
yr<SUP>-1</SUP>. Their median stellar mass is log
(M<SUB>*</SUB>/M<SUB>⊙</SUB>) = 9.74. We find that the
dust-corrected total SFR of LBGs increases with stellar mass and that
the specific SFR is lower for more massive galaxies (downsizing
scenario). Only 2 per cent of the galaxies selected through the Lyman
break criterion have an active galactic nucleus nature. LBGs at z
˜ 1 are located mostly over the blue cloud of the colour-magnitude
diagram of galaxies at their redshift, with only the oldest and/or the
dustiest deviating towards the green valley and red sequence.
Morphologically, 69 per cent of LBGs are disc-like galaxies, with the
fractions of interacting, compact, or irregular systems being much
lower, below 12 per cent. LBGs have a median effective radius of 2.5
kpc, and larger galaxies have a higher total SFR and stellar mass.
Compared with their high-redshift analogues, we find evidence that LBGs
at lower redshifts are larger, redder in the UV continuum, and have a
major presence of older stellar populations in their SEDs. However, we
do not find significant differences in the distributions of stellar mass
or dust attenuation.