The star formation history and metal content of the "Green Peas". New
  detailed GTC-OSIRIS spectrophotometry of three galaxies
  We present deep broad-band imaging and long-slit spectroscopy of three
compact, low-mass starburst galaxies at redshift z\sim0.2-0.3, also referred to
as Green Peas (GP). We measure physical properties of the ionized gas and
derive abundances for several species with high precision. We find that the
three GPs display relatively low extinction, low oxygen abundances, and
remarkably high N/O ratios We also report on the detection of clear signatures
of Wolf-Rayet (WR) stars in these galaxies. We carry out a pilot spectral
synthesis study using a combination of both population and evolutionary
synthesis models. Their outputs are in qualitative agreement, strongly
suggesting a formation history dominated by starbursts. In agreement with the
presence of WR stars, these models show that these GPs currently undergo a
major starburst producing between ~4% and ~20% of their stellar mass. However,
as models imply, they are old galaxies having had formed most of their stellar
mass several Gyr ago. The presence of old stars has been spectroscopically
verified in one of the galaxies by the detection of Mg I 5167, 5173 absorption
line. Additionally, we perform a surface photometry study based on HST data,
that indicates that the three galaxies posses an exponential low-surface
brightness envelope. If due to stellar emission, the latter is structurally
compatible to the evolved hosts of luminous BCD/HII galaxies, suggesting that
GPs are identifiable with major episodes in the assembly history of local BCDs.
These conclusions highlight the importance of these objects as laboratories for
studying galaxy evolution at late cosmic epochs.
