292 research outputs found
Kinematic Properties and Dark Matter Fraction of Virgo Dwarf Early-Type Galaxies
What happens to dwarf galaxies as they enter the cluster potential well is
one of the main unknowns in studies of galaxy evolution. Several evidence
suggests that late-type galaxies enter the cluster and are transformed to dwarf
early-type galaxies (dEs). We study the Virgo cluster to understand which
mechanisms are involved in this transformation. We find that the dEs in the
outer parts of Virgo have rotation curves with shapes and amplitudes similar to
late-type galaxies of the same luminosity. These dEs are rotationally
supported, have disky isophotes, and younger ages than those dEs in the center
of Virgo, which are pressure supported, often have boxy isophotes and are
older. Ram pressure stripping, thus, explains the properties of the dEs located
in the outskirts of Virgo. However, the dEs in the central cluster regions,
which have lost their angular momentum, must have suffered a more violent
transformation. A combination of ram pressure stripping and harassment is not
enough to remove the rotation and the spiral/disky structures of these
galaxies. We find that on the the Faber-Jackson and the Fundamental Plane
relations dEs deviate from the trends of massive elliptical galaxies towards
the position of dark matter dominated systems such as the dwarf spheroidal
satellites of the Milky Way and M31. Both, rotationally and pressure supported
dEs, however, populate the same region in these diagrams. This indicates that
dEs have a non-negligible dark matter fraction within their half light radius.Comment: Proceeding of the XXVIII IAU General Assembly, Special Session 3:
Galaxy Evolution through Secular Processes. Edts: R. Buta and D. Pfennige
NH and Mg Index Trends in Elliptical Galaxies
We examine the spectrum in the vicinity of the NH3360 index of Davidge &
Clark (1994), which was defined to measure the NH absorption around 3360 \AA
and which shows almost no trend with velocity dispersion (Toloba et al. 2009),
unlike other N- sensitive indices, which show a strong trend (Graves et al.
2007). Computing the effect of individual elements on the integrated spectrum
with synthetic stellar population integrated spectra, we find that, while being
well correlated with nitrogen abundance, NH3360 is almost equally well
anti-correlated with Mg abundance. This prompts the definition of two new
indices, Mg3334, which is mostly sensitive to magnesium, and NH3375, which is
mostly sensitive to nitrogen. Rather surprisingly, we find that the new NH3375
index shows a trend versus optical absorption feature indices that is as
shallow as the NH3360 index. We hypothesize that the lack of a strong index
trend in these near-UV indices is due to the presence of an old metal-poor
component of the galactic population. Comparison of observed index trends and
those predicted by models shows that a modest fraction of an old, metal-poor
stellar population could easily account for the observed flat trend in these
near-UV indices, while still allowing substantial N abundance increase in the
larger galaxies.Comment: 19 pages, 6 figures, 6 table
Formation and evolution of dwarf early-type galaxies in the Virgo cluster II. Kinematic Scaling Relations
We place our sample of 18 Virgo dwarf early-type galaxies (dEs) on the V-K -
velocity dispersion, Faber-Jackson, and Fundamental Plane (FP) scaling
relations for massive early-type galaxies (Es). We use a generalized velocity
dispersion, which includes rotation, to be able to compare the location of both
rotationally and pressure supported dEs with those of early and late-type
galaxies. We find that dEs seem to bend the Faber-Jackson relation of Es to
lower velocity dispersions, being the link between Es and dwarf spheroidal
galaxies (dSphs). Regarding the FP relation, we find that dEs are significantly
offset with respect to massive hot stellar systems, and re-casting the FP into
the so-called kappa-space suggests that this offset is related to dEs having a
total mass-to-light ratio higher than Es but still significantly lower than
dSph galaxies. Given a stellar mass-to-light ratio based on the measured line
indices of dEs, the FP offset allows us to infer that the dark matter fraction
within the half light radii of dEs is on average >~ 42% (uncertainties of 17%
in the K band and 20% in the V band), fully consistent with an independent
estimate in an earlier paper in this series. We also find that dEs in the
size-luminosity relation in the near-infrared, like in the optical, are offset
from early-type galaxies, but seem to be consistent with late-type galaxies. We
thus conclude that the scaling relations show that dEs are different from Es,
and that they further strengthen our previous findings that dEs are closer to
and likely formed from late-type galaxies.Comment: 14 pages, 9 figures, 2 appendixes. Accepted for publication in A&
Color-Magnitude Relations of Early-type Dwarf Galaxies in the Virgo Cluster: An Ultraviolet Perspective
We present ultraviolet (UV) color-magnitude relations (CMRs) of early-type
dwarf galaxies in the Virgo cluster, based on Galaxy Evolution Explorer (GALEX)
UV and Sloan Digital Sky Survey (SDSS) optical imaging data. We find that dwarf
lenticular galaxies (dS0s), including peculiar dwarf elliptical galaxies (dEs)
with disk substructures and blue centers, show a surprisingly distinct and
tight locus separated from that of ordinary dEs, which is not clearly seen in
previous CMRs. The dS0s in UV CMRs follow a steeper sequence than dEs and show
bluer UV-optical color at a given magnitude. We also find that the UV CMRs of
dEs in the outer cluster region are slightly steeper than that of their
counterparts in the inner region, due to the existence of faint, blue dEs in
the outer region. We explore the observed CMRs with population models of a
luminosity-dependent delayed exponential star formation history. We confirm
that the feature of delayed star formation of early-type dwarf galaxies in
Virgo cluster is strongly correlated with their morphology and environment. The
observed CMR of dS0s is well matched by models with relatively long delayed
star formation. Our results suggest that dS0s are most likely transitional
objects at the stage of subsequent transformation of late-type progenitors to
ordinary red dEs in the cluster environment. In any case, UV photometry
provides a powerful tool to disentangle the diverse subpopulations of
early-type dwarf galaxies and uncover their evolutionary histories.Comment: 6 pages, 2 figures, 1 table, accepted for publication in the ApJ
- …