796 research outputs found
A SAURON study of dwarf elliptical galaxies in the Virgo Cluster
Dwarf elliptical galaxies are the most common galaxy type in nearby galaxy
clusters, yet they remain relatively poorly studied objects and many of their
basic properties have yet to be quantified. In this contribution we present the
preliminary results of a study of 4 Virgo and 1 field galaxy obtained with the
SAURON integral field unit on the William Herschel Telescope (La Palma). While
traditional long-slit observations are likely to miss more complicated
kinematic features, with SAURON we are able to study both kinematics and
stellar populations in two dimensions, obtaining a much more detailed view of
the mass distribution and star formation histories.Comment: 2 pages, 1 figure; to appear in the proceedings of the conference "A
Universe of dwarf galaxies" (Lyon, June 14-18, 2010
Spectroscopic characterisation of the stellar content of ultra diffuse galaxies
Understanding the peculiar properties of Ultra Diffuse Galaxies (UDGs) via
spectroscopic analysis is a challenging task requiring very deep observations
and exquisite data reduction. In this work we perform one of the most complete
characterisations of the stellar component of UDGs to date using deep optical
spectroscopic data from OSIRIS at GTC. We measure radial and rotation
velocities, star formation histories (SFH) and mean population parameters, such
as ages and metallicities, for a sample of five UDG candidates in the Coma
cluster. From the radial velocities, we confirm the Coma membership of these
galaxies. We find that their rotation properties, if detected at all, are
compatible with dwarf-like galaxies. The SFHs of the UDG are dominated by old
(~ 7 Gyr), metal-poor ([M/H] ~ -1.1) and alpha-enhanced ([Mg/Fe] ~ 0.4)
populations followed by a smooth or episodic decline which halted ~ 2 Gyr ago,
possibly a sign of cluster-induced quenching. We find no obvious correlation
between individual SFH shapes and any UDG morphological properties. The
recovered stellar properties for UDGs are similar to those found for DDO44, a
local UDG analogue resolved into stars. We conclude that the UDGs in our sample
are extended dwarfs whose properties are likely the outcome of both internal
processes, such as bursty SFHs and/or high-spin haloes, as well as
environmental effects within the Coma cluster.Comment: Accepted for publication in MNRA
The Fornax Deep Survey with VST. VIII. Connecting the accretion history with the cluster density
This work is based on deep multi-band (g, r, i) data from the Fornax Deep
Survey with VST. We analyse the surface brightness profiles of the 19 bright
ETGs inside the virial radius of the Fornax cluster. The main aim of this work
is to identify signatures of accretion onto galaxies by studying the presence
of outer stellar halos, and understand their nature and occurrence. Our
analysis also provides a new and accurate estimate of the intra-cluster light
inside the virial radius of Fornax. We performed multi-component fits to the
azimuthally averaged surface brightness profiles available for all sample
galaxies. This allows to quantify the relative weight of all components in the
galaxy structure that contribute to the total light. In addition, we derived
the average g-i colours in each component identified by the fit, as well as the
azimuthally averaged g-i colour profiles, to correlate them with the stellar
mass of each galaxy and the location inside the cluster. We find that in the
most massive and reddest ETGs the fraction of light in, probably accreted,
halos is much larger than in the other galaxies. Less-massive galaxies have an
accreted mass fraction lower than 30%, bluer colours and reside in the
low-density regions of the cluster. Inside the virial radius of the cluster,
the total luminosity of the intra-cluster light, compared with the total
luminosity of all cluster members, is about 34%. Inside the Fornax cluster
there is a clear correlation between the amount of accreted material in the
stellar halos of galaxies and the density of the environment in which those
galaxies reside. By comparing this quantity with theoretical predictions and
previous observational estimates, there is a clear indication that the driving
factor for the accretion process is the total stellar mass of the galaxy, in
agreement with the hierarchical accretion scenario.Comment: 18 pages, 10 figures. Accepted for publication in A&
Carbon stars in the X-shooter Spectral Library
We provide a new collection of spectra of 35 carbon stars obtained with the
ESO/VLT X-shooter instrument as part of the X-shooter Spectral Library project.
The spectra extend from 0.3m to 2.4m with a resolving power above
8000. The sample contains stars with a broad range of (J-K) color and
pulsation properties located in the Milky Way and the Magellanic Clouds. We
show that the distribution of spectral properties of carbon stars at a given
(J-K) color becomes bimodal (in our sample) when (J-K) is larger than about
1.5. We describe the two families of spectra that emerge, characterized by the
presence or absence of the absorption feature at 1.53m, generally
associated with HCN and CH. This feature appears essentially only in
large-amplitude variables, though not in all observations. Associated spectral
signatures that we interpret as the result of veiling by circumstellar matter,
indicate that the 1.53m feature might point to episodes of dust production
in carbon-rich Miras.Comment: 29 pages, 21 figures, 9 tables, Accepted for publication in A&
Minor axis kinematics of 19 S0-Sbc bulges
We present minor axis kinematic profiles for a well-studied sample of 19
early- to intermediate-type disk galaxies. We introduce, for the first time,
the use of single-burst stellar population (SSP) models to obtain stellar
velocities, velocity dispersions and higher order Gauss-Hermite moments (h3,h4)
from galaxy spectra in the near-infrared Ca II triplet region. SSP models,
which employs the synthetic spectra of Vazdekis et al. 2003, provide a means to
address the template-mismatch problem, and are shown to provide as good or
better fits as traditional stellar templates. We anticipate the technique to be
of particular use for high-redshift galaxy kinematics. We give the measurement
of a recently defined CaT* index Cenarro et al. 2001a, and describe the global
properties of the bulge kinematics as derived from the kinematic profiles. We
detect small-amplitude minor-axis rotation, generally due to inner isophotal
twists as a result of slightly triaxial bulges or misaligned inner disks; such
inner features do not show peculiar colors or distinct CaT* index values.
Velocity dispersion profiles, which extend well into the disk region, show a
wide range of slopes. Flattened bulges tend to have shallower velocity
dispersion profiles. The inferred similarity of bulge and disk radial velocity
dispersions supports the interpretation of these bulges as thickened disks.Comment: 18 pages, 28 figures (9 images in main body, 19 low resolution images
in appendix A), the preprint with high resolution images can be downloaded
from http://astro.nottingham.ac.uk/~jfalcon/galaxies.php (2.6MB). Accepted
for publication in A&
Quantifying Resonant Structure in NGC 6946 from Two-dimensional Kinematics
We study the two-dimensional kinematics of the H-alpha-emitting gas in the
nearby barred Scd galaxy, NGC 6946, in order to determine the pattern speed of
the primary m=2 perturbation mode. The pattern speed is a crucial parameter for
constraining the internal dynamics, estimating the impact velocities of the
gravitational perturbation at the resonance radii, and to set up an
evolutionary scenario for NGC 6946. Our data allows us to derive the best
fitting kinematic position angle and the geometry of the underlying gaseous
disk, which we use to derive the pattern speed using the Tremaine-Weinberg
method. We find a main pattern speed Omega_p=22 km/s/kpc, but our data clearly
reveal the presence of an additional pattern speed Omega_p=47 km/s/kpc in a
zone within 1.25 kpc of the nucleus. Using the epicyclic approximation, we
deduce the location of the resonance radii and confirm that inside the outer
Inner Lindblad Resonance radius of the main oval, a primary bar has formed
rotating at more than twice the outer pattern speed. We further confirm that a
nuclear bar has formed inside the Inner Lindblad Resonance radius of the
primary bar, coinciding with the inner Inner Lindblad Resonance radius of the
large-scale m=2 mode oval.Comment: Accepted for publication in ApJ Letter
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