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| Paper IPM / Astronomy / 14692 |
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| Abstract: | |||||||
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We investigate how the stellar populations of the inner regions of the first and the second
brightest group galaxies (respectively BGGs and SBGGs) vary as a function of magnitude gap,
using an SDSS-based sample of 550 groups with elliptical BGGs. The sample is complete in
redshift, luminosity and for �??M12 up to 2.5 mag, and contains 59 large-gap groups (LGGs,
with �??M12 > 2.0 mag). We determine ages, metallicities, and SFHs of BGGs and SBGGs
using the STARLIGHT code with two different single stellar population models (which lead
to important disagreements in SFHs), and also compute [α/Fe] from spectral indices. After
removing the dependence with galaxy velocity dispersion or with stellar mass, there is no
correlation with magnitude gap of BGG ages, metallicities, [α/Fe], and SFHs. The lack of
trends of BGG SFHs with magnitude gap suggests that BGGs in LGGs have undergone more
mergers than those in small-gap groups, but these mergers are either dry or occurred at very
high redshift, which in either case would leave no detectable imprint in their spectra. We
show that SBGGs in LGGs lie significantly closer to the BGGs (in projection) than galaxies
with similar stellar masses in normal groups, which appears to be a sign of the earlier entry
of the former into their groups. Nevertheless, the stellar population properties of the SBGGs
in LGGs are compatible with those of the general population of galaxies with similar stellar
masses residing in normal groups
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