Star-forming galaxies at low-redshift in the SHARDS survey
  The physical processes driving the evolution of star formation (SF) in
galaxies over cosmic time still present many open questions. Recent galaxy
surveys allow now to study these processes in great detail at intermediate
redshift. In this work, we build a complete sample of star-forming galaxies and
analyze their properties, reaching systems with low stellar masses and low star
formation rates (SFRs) at intermediate-to-low redshift. We use data from the
SHARDS multiband survey in the GOODS-North field. Its depth (up to magnitude
$\langle m_{3\sigma}\rangle\sim26.5$) and its spectro-photometric resolution
($R\sim50$) provides us with an ideal dataset to search for emission line
galaxies (ELGs). We develop a new algorithm to identify low-redshift ($z$<0.36)
ELGs by detecting the [OIII]5007 and $H\alpha$ emission lines simultaneously.
We fit the spectral energy distribution (SED) of the selected sample, using a
model with two single stellar populations. We find 160 star-forming galaxies
with equivalent widths (EWs) as low as 12 {\AA}, with median values for the
sample of $\sim$ 35 {\AA} in [OIII]5007 and $\sim$ 56 {\AA} in $H\alpha$,
respectively. Results from the SED fitting show a young stellar population with
low median metallicity (36% of the solar value) and extinction ($A_V \sim$
0.37), with median galaxy stellar mass $\sim$ 10$^{8.5}$ M$_{\odot}$. Gas-phase
metallicities measured from available spectra are also low. ELGs in our sample
present bluer colors in the UVJ plane than the median color-selected
star-forming galaxy in SHARDS. We suggest a new (V-J) color criterion to
separate ELGs from non-ELGs in blue galaxy samples. In addition, several
galaxies present high densities of O-type stars. Robust fits to the full SEDs
can only be obtained including an old stellar population, suggesting the young
component is built up by a recent burst of SF in an otherwise old galaxy.
