For refcode 1999MNRAS.306..607J: Retrieve 128 NED objects in this reference. Please click here for ADS abstract
NED Abstract
Copyright by Royal Astronomical Society.
1999MNRAS.306..607J
E and S0 galaxies in the central part of the Coma cluster: ages, metal
abundances and dark matter
Ingor Jorgensen
Accepted 1999 February 9. Received 1998 December 22; in original form 1998
August 24
ABSTRACT
Mean ages and metal abundances are estimated for the stellar populations in
a sample of 115 E and S0 galaxies in the central 64 arcmin x 70 arcmin of
the Coma cluster. The estimates are based on the absorption line indices
Mg_2_, <Fe> and H{beta}_G_, and the masstolight ratios (M/L). Single
stellar population models from Vazdekis et al. were used to transform from
the measured line indices and M/L ratios to mean ages and mean metal
abundances ([Mg/H] and [Fe/H]). The nonsolar abundance ratios [Mg/Fe] were
taken into account by assuming that for a given age and iron abundance, a
[Mg/Fe] different from solar will affect the Mg_2_ index but not the M/L
ratio or the <Fe> and H{beta}_G_ indices. The derived ages and abundances
are the luminosityweighted mean values for the stellar populations in the
galaxies.
By comparing the mean ages derived from the Mg_2_H{beta}_G_ diagram
with those derived from the Mg_2_M/L diagram, we estimate the variations
of the fraction of dark matter. Alternatively, the difference between the
two estimates of the mean age may be caused by variations in the initial
mass function or any nonhomology of the galaxies.
The distributions of the derived mean ages and abundances show that
there are real variations in both the mean ages and the abundances. We find
an intrinsic rms scatter of [Mg/H], [Fe/H] and [Mg/Fe] of 0.2 dex, and an
intrinsic rms scatter of the derived ages of 0.17 dex. The magnesium
abundances [Mg/H] and the abundance ratios [Mg/Fe] are both strongly
correlated with the central velocity dispersions of the galaxies, while the
iron abundances [Fe/H] are uncorrelated with the velocity dispersions.
Further, [Mg/H] and [Fe/H] are strongly anticorrelated with the mean ages
of the galaxies. This is not the case for [Mg/Fe].
We have tested whether the slopes of the scaling relations between the
global parameters for the galaxies (the Mg_2_{sigma} relation, the <Fe>
{sigma} relation, the H{beta}_G_{sigma} relation and the Fundamental
Plane) are consistent with the relation between the ages, the abundances
and the velocity dispersions. We find that all the slopes, except the slope
of the Fundamental Plane, can be explained in a consistent way as resulting
from a combination between variations of the mean ages and the mean
abundances as functions of the velocity dispersions. The slope of the
Fundamental Plane is 'steeper' than predicted from the variations in the
ages and abundances.
Because of the correlation between the mean ages and the mean
abundances, substantial variations in the ages and the abundances are
possible while maintaining a low scatter of all the scaling relations. When
this correlation is taken into account, the observed scatter of the scaling
relations is consistent with the rms scatter in the derived ages and
abundances at a given velocity dispersion.
Keywords: galaxies: clusters: individual: Coma  galaxies: elliptical and
lenticular, cD  galaxies: fundamental parameters  galaxies: stellar
content  dark matter
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