Low-Redshift Ly-alpha Selected Galaxies from GALEX Spectroscopy: A
  Comparison with Both UV-Continuum Selected Galaxies and High-Redshift
  Ly-alpha Emitters
  We construct a sample of low-redshift Ly-alpha emission-line selected sources
from GALEX grism spectroscopy of nine deep fields to study the role of Ly-alpha
emission in galaxy populations with cosmic time. Our final sample consists of
119 (141) sources selected in the redshift interval z=0.195-0.44 (z=0.65-1.25)
from the FUV (NUV) channel. We classify the Ly-alpha sources as AGNs if
high-ionization emission lines are present in their UV spectra and as possible
star-forming galaxies otherwise. We classify additional sources as AGNs using
line widths for our Ly-alpha emitter (LAE) analysis. These classifications are
broadly supported by comparisons with X-ray and optical spectroscopic
observations. Defining the GALEX LAE sample in the same way as high-redshift
LAE samples, we show that LAEs constitute only about 5% of NUV-continuum
selected galaxies at z~0.3. We also show that they are less common at z~0.3
than they are at z~3. We find that the z~0.3 optically-confirmed Ly-alpha
galaxies lie below the metallicity-luminosity relation of the z~0.3
NUV-continuum selected galaxies but have similar H-alpha velocity widths at
similar luminosities, suggesting that they also lie below the metallicity-mass
relation of the NUV-continuum selected galaxies. We show that, on average, the
Ly-alpha galaxies have bluer colors, lower extinctions as measured from the
Balmer line ratios, and more compact morphologies than the NUV-continuum
selected galaxies. Finally, we confirm that the z~2 Lyman break galaxies (LBGs)
have relatively low metallicities for their luminosities, and we find that they
lie in the same metallicity range as the z~0.3 Ly-alpha galaxies.
