Bibcode
Koleva, M.; Prugniel, Philippe; de Rijcke, Sven; Zeilinger, Werner W.
Referencia bibliográfica
Monthly Notices of the Royal Astronomical Society, Volume 417, Issue 3, pp. 1643-1671.
Advertised on:
11
2011
Número de citas
118
Número de citas referidas
110
Descripción
We studied the stellar populations of 40 early-type galaxies using
medium-resolution long-slit spectroscopy along their major axes (and
along the minor axis for two of them). The sample, including elliptical
and lenticular galaxies as well as dwarf galaxies, is combined with
other previously published data in order to discuss the systematics of
the radial gradients of age and metallicity over a large mass range,
from 107 M&sun; to 1012
M&sun; (-9.2 > MB > -22.4 mag). The
well-known mass-metallicity relation is continuous throughout the whole
mass range, in the sense that more massive galaxies are more metal-rich.
The age-mass relation is consistent with the idea of downsizing: smaller
galaxies have more extended star formation histories than more massive
ones. The transition-type dwarfs (intermediate between dwarf irregular
and dwarf elliptical galaxies) deviate from this relation having younger
mean age, and the low-mass dwarf spheroidals have older ages, marking a
discontinuity in the relation, possibly due to selection effects.
In all mass regimes, the mean metallicity gradients are approximately
-0.2 and the mean age gradients +0.1 dex per decade of radius. The
individual gradients are widely spread: -0.1 < ∇Age
< 0.4 and -0.54 < ∇[Fe/H] < +0.2. We do not
find evidence for a correlation between the metallicity gradient and
luminosity, velocity dispersion, central age or age gradient. Likewise,
we do not find a correlation between the age gradient and any other
parameter in bright early-type galaxies. In faint early-types with
MB≳-17 mag, on the other hand, we find a strong
correlation between the age gradient and luminosity: the age gradient
becomes more positive for fainter galaxies. Together with the observed
downsizing phenomenon this indicates that, as time passes, star
formation persists in dwarf galaxies and becomes more centrally
concentrated. However, this prolonged central star formation is not
reflected in the metallicity profiles of the dwarfs in our sample.
We conclude that various physical mechanisms can lead to similar
gradients and that these gradients are robust against the environmental
effects. In particular, the gradients observed in dwarf galaxies
certainly survived the transformation of the progenitors through tidal
harassment or/and ram-pressure stripping. The diversity of metallicity
gradients amongst dwarf elliptical galaxies may reflect a plurality of
progenitors' morphologies. The dwarfs with steep metallicity gradients
could have originated from blue compact dwarfs and those with flat
profiles from dwarf irregulars and late-type spirals.
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