1,781 research outputs found
Stellar populations of seven early-type dwarf galaxies and their nuclei
Dwarf galaxies are the numerically dominating population in the dense regions
of the universe. Although they seem to be simple systems at first view, the
stellar populations of dwarf elliptical galaxies (dEs) might be fairly complex.
Nucleated dEs are of particular interest, since a number of objects exhibit
different stellar populations in their nuclei and host galaxy. We present
stellar population parameters obtained from integrated optical spectra using a
Lick index analysis of seven nucleated dwarf elliptical galaxies and their
nuclei. After subtracting the scaled galaxy spectra from the nucleus spectra,
we compared them with one another and explore their stellar populations. As a
preliminary result, we find that the luminosity weighted ages of the nuclei
slightly lower than those of galaxies, however, we do not see any significant
difference in metallicity of the host galaxies and their nuclei.Comment: 3 pages, 3 figures, to be published in Astronomische Nachrichten
(proceedings of Symposium 6 of the JENAM 2008, Vienna
Dissecting early-type dwarf galaxies into their multiple components
Early-type dwarf galaxies, once believed to be simple systems, have recently
been shown to exhibit an intriguing diversity in structure and stellar content.
To analyze this further, we started the SMAKCED project, and obtained deep
H-band images for 101 early-type dwarf galaxies in the Virgo cluster in a
brightness range of -19 \leq M_r \leq -16 mag, typically reaching a
signal-to-noise of 1 per pixel of \sim0.25" at surface brightnesses \sim22.5
mag/arcsec^2 in the H-band. Here we present the first results of decomposing
their two-dimensional light distributions. This is the first study dedicated to
early-type dwarf galaxies using the two-dimensional multi-component
decomposition approach, which has been proven to be important for giant
galaxies. Armed with this new technique, we find more structural components
than previous studies: only a quarter of the galaxies fall into the simplest
group, namely those represented by a single S\'ersic function, optionally with
a nucleus. Furthermore, we find a bar fraction of 18%. We detect also a similar
fraction of lenses which appear as shallow structures with sharp outer edges.
Galaxies with bars and lenses are found to be more concentrated towards the
Virgo galaxy center than the other sample galaxies.Comment: Accepted by ApJL, 6 pages, 4 figures, 1 tabl
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
On the Color Magnitude Relation of Early-type Galaxies
In this letter we present a study of the color magnitude relation of 468
early-type galaxies in the Virgo Cluster with Sloan Digital Sky Survey imaging
data. The analysis of our homogeneous, model-independent data set reveals that,
in all colors (u-g, g-r, g-i, i-z) similarly, giant and dwarf early-type
galaxies follow a continuous color magnitude relation (CMR) that is best
described by an S-shape. The magnitude range and quality of our data allows us
to clearly confirm that the CMR in Virgo is not linear. Additionally, we
analyze the scatter about the CMR and find that it increases in the
intermediate-luminosity regime. Nevertheless, despite this observational
distinction, we conclude from the similarly shaped CMR of semi-analytic model
predictions that dwarfs and giants could be of the same origin.Comment: Accepted by ApJL; 5 pages, 3 figures; added missing line to Figure
Universal chiral conductivities for low temperature holographic superfluids
We argue that the chiral conductivities of generic s-wave holographic
superfluids, whose broken U(1) symmetry is anomalous, exhibit universal
behavior at low temperatures. The universal behavior we argue for is
independent of the details of the bulk action and on the emergent geometry deep
in the bulk interior at low temperatures. Our results are contrasted against
general expectations based on an analysis of the entropy current in
superfluids.Comment: 14 pages, 2 figure
A continuum of structure and stellar content from Virgo cluster early-type dwarfs to giants?
Based on the wealth of multiwavelength imaging data from the SDSS, we
investigate whether dwarf and giant early-type galaxies in the Virgo cluster
follow a continuum in their structural parameters and their stellar population
characteristics. More specifically we study the relation between size and
brightness for the galaxies and their color magnitude relation. In both cases,
we find noticeable deviations from a simple joint behavior of dwarfs and
giants. We discuss these findings in the light of the different formation
mechanisms commonly assumed for dwarf and giant early types, thereby taking
into account the existence of several distinct early-type dwarf subclasses. By
comparing our results to a semianalytic model of galaxy formation, we argue
that the analyzed relations might be reproduced by processes that form dwarfs
and giants altogether. The work presented here is based on Janz & Lisker 2008,
2009.Comment: 7 pages, 3 figures, to be published in Astronomische Nachrichten
(proceedings of Symposium 6 of the JENAM 2008, Vienna
Exploring the formation of spheroidal galaxies out to z ∼ 1.5 in GOODS
The formation of massive spheroidal galaxies is studied on a visually classified sample extracted from the Advanced Camera for Surveys/Hubble Space Telescope (ACS/HST) images of the Great Observatories Origins Deep Survey north and south fields, covering a total area of 360 arcmin . The sample size (910 galaxies brighter than i = 24) allows us to explore in detail the evolution over a wide range of redshifts (0.4 10 M galaxies by a factor of 2 between z = 1 and 0, in contrast with a factor of ∼50 for lower mass galaxies (10 <M / M <10 ). One-quarter of the whole sample of early types are photometrically classified as blue galaxies. On a volume-limited sample out to z <0.7, the average stellar mass of the blue ellipticals is 5 × 10 M compared to 4 × 10 M for red ellipticals. On a volume-limited subsample out to z = 1.4 probing the brightest galaxies (M <-21), we find the median redshift of blue and red early types: 1.10 and 0.85, respectively. Blue early types only amount to 4 per cent of this sample (compared to 26 per cent in the full sample). The intrinsic colour distribution correlates overall bluer colours with blue cores (positive radial gradients of colour), suggesting an inside-out process of formation. The redshift evolution of the observed colour gradients is incompatible with a significant variation in stellar age within each galaxy. The slope of the Kormendy relation in the subsample of massive galaxies does not change over 0.4 <z <1.4 and is compatible with z = 0 values. The 'zero-point' of the Kormendy relation (i.e. the surface brightness at a fixed half-light radius) is 1 mag fainter (in the B band) for the subsample of low-mass (M <3.5 × 10 M ) early types.Peer reviewe
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