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We examine the metallicity and age of a large set of SDSS/DR6 galaxies that may be Blue Compact Dwarf (BCD) galaxies during quiescence (QBCDs).The individual spectra are first classified and then averaged to reduce noise. The metallicity inferred from emission lines (tracing ionized gas) exceeds by ~0.35 dex the metallicity inferred from absorption lines (tracing stars). Such a small difference is significant according to our error budget estimate. The same procedure was applied to a reference sample of BCDs, and in this case the two metallicities agree, being also consistent with the stellar metallicity in QBCDs. Chemical evolution models indicate that the gas metallicity of QBCDs is too high to be representative of the galaxy as a whole, but it can represent a small fraction of the galactic gas, self enriched by previous starbursts. The luminosity weighted stellar age of QBCDs spans the whole range between 1 and 10 Gyr, whereas it is always smaller than 1 Gyr for BCDs. Our stellar ages and metallicities rely on a single stellar population spectrum fitting procedure, which we have specifically developed for this work using the stellar library MILES.
This is the fourth paper in a series studying star formation rates, stellar components, metallicities, and star formation histories of a blue compact galaxy (BCG) sample. Using Ha, [OII]3727, IR, radio (1.4GHz) luminosities and neutral hydrogen gas m
Dwarf galaxies are generally faint. To derive their age and metallicity distributions, it is critical to optimize the use of any collected photon. Koleva et al., using full spectrum fitting, have found strong population gradients in some dwarf ellipt
We study dwarf galaxy formation at high redshift ($zge5$) using a suite of high- resolution, cosmological hydrodynamic simulations and a semi-analytic model (SAM). We focus on gas accretion, cooling and star formation in this work by isolating the re
We present Spitzer IRS spectra and MIPS photometry of 12 radio-loud QSOs with FR II morphologies at z ~ 0.3. Six of the sources are surrounded by luminous extended emission-line regions (EELRs), while the other six do not have such extended nebulae.
We present optical VLT spectroscopy of 16 dwarf elliptical galaxies (or dEs) comparable in mass to NGC 205, and belonging to the Fornax cluster and to nearby groups of galaxies. Using ULySS and STECKMAP, we derive radial profiles of the SSP-equivalen