1,144 research outputs found
Constraining the ages of the fireballs in the wake of the dIrr galaxy VCC1217 / IC3418
A complex of Halpha emitting blobs with strong FUV excess is associated to
the dIrr galaxy VCC1217 / IC3418 (Hester et al. 2010), and extends up to 17 Kpc
in the South-East direction. These outstanding features can be morphologically
divided into diffuse filaments and compact knots, where most of the star
formation activity traced by Halpha takes place. We investigate the properties
of the galaxy and the blobs using a multiwavelength approach in order to
constrain their origin. We collect publicly available data in UV and Halpha and
observe the scene in the optical U,g,r,i bands with LBT. The photometric data
allows to evaluate the star formation rate and to perform a SED fitting
separately of the galaxy and the blobs in order to constrain their stellar
population age. Moreover we analyze the color and luminosity profile of the
galaxy and its spectrum to investigate its recent interaction with the Virgo
cluster. Our analysis confirms that the most plausible mechanism for the
formation of the blobs is ram pressure stripping by the Virgo cluster IGM. The
galaxy colors, luminosity profile and SED are consistent with a sudden gas
depletion in the last few hundred Myr. The SED fitting of the blobs constrains
their ages in < 400 Myr.Comment: 10 pages, 11 figures, accepted for publication in Astronomy and
Astrophysic
Radio continuum spectra of galaxies in the Virgo cluster region
New radio continuum observations of galaxies in the Virgo cluster region at
4.85, 8.6, and 10.55 GHz are presented. These observations are combined with
existing measurements at 1.4 and 0.325 GHz. The sample includes 81 galaxies
were spectra with more than two frequencies could be derived. Galaxies that
show a radio-FIR excess exhibit central activity (HII, LINER, AGN). The four
Virgo galaxies with the highest absolute radio excess are found within 2
degrees of the center of the cluster. Galaxies showing flat radio spectra also
host active centers. There is no clear trend between the spectral index and the
galaxy's distance to the cluster center.Comment: 13 pages, 12 figures. Accepted for publication in A&
A radial mass profile analysis of the lensing cluster MS2137-23
We reanalyze the strong lens modeling of the cluster of galaxies MS2137-23
using a new data set obtained with the ESO VLT. We found the photometric
redshifts of the two main arc systems are both at z=1.6. After subtraction of
the central cD star light of the HST image we found that only one object lying
underneath has the expected properties of the fifth image associated to the
tangential arc. We improve the previous lens modelings of the central dark
matter distribution of the cluster, using an isothermal model with a core (IS)
and the NFW-like model with a cusp. Without the fifth image, the arc properties
together with the shear map profile are equally well fit by the and by an IS
and a sub-class of generalized-NFW mass profiles having inner slope power index
in the range 0.7<alpha<1.2. Adding new constrains provided by the fifth image
favors IS profiles that better predict the fifth image properties. A model
including cluster galaxy perturbations or the the stellar mass distribution
does not change our conclusions but imposes the M/L_I of the cD stellar
component is below 10 at a 99% confidence level.
Using our new detailed lensing model together with Chandra X-ray data and the
cD stellar component we finally discuss intrinsic properties of the
gravitational potential. Whereas X-ray and dark matter have a similar shape at
various radius, the cD stellar isophotes are twisted by 13 deg. The sub-
arc-second azimuthal shift we observe between the radial arc position and the
predictions of elliptical models correspond to what is expected from a mass
distribution twist. This shift may result from a projection effect of the cD
and the cluster halos, thus revealing the triaxiality of the system.Comment: Final version accepted in A&
The census of nuclear activity of late-type galaxies in the Virgo cluster
The first spectroscopic census of AGNs associated to late-type galaxies in
the Virgo cluster is carried on by observing 213 out of a complete set of 237
galaxies more massive than M_dyn>10^{8.5} solar masses. Among them, 77 are
classified as AGNs (including 21 transition objects, 47 LINERs and 9 Seyferts),
and comprize 32% of the late-type galaxies in Virgo. Due to spectroscopic
incompleteness at most 21 AGNs are missed in the survey, so that the fraction
would increase up to 41%. Using corollary Near-IR observations, that enable us
to estimate galaxies dynamical masses, it is found that AGNs are hosted
exclusively in massive galaxies, i.e. M_dyn\gsim 10^{10} solar masses. Their
frequency increases steeply with the dynamical mass from zero at
M_dyn\approx10^{9.5} solar masses to virtually 1 at M_dyn>10^{11.5} solar
masses. These frequencies are consistent with the ones of low luminosity AGNs
found in the general field by the SDSS. Massive galaxies that harbor AGNs
commonly show conspicuous r-band star-like nuclear enhancements. Conversely
they often, but not necessarily contain massive bulges. Few well known AGNs
(e.g. M61, M100, NGC4535) are found in massive Sc galaxies with little or no
bulge. The AGN fraction seems to be only marginally sensitive to galaxy
environment. We infer the black hole masses using the known scaling relations
of quiescent black holes. No black holes lighter than \msol are
found active in our sample.Comment: The paper contains 13 figures and 5 tables; accepted for publication
in MNRA
The Dark UNiverse Explorer (DUNE): Proposal to ESA's Cosmic Vision
The Dark UNiverse Explorer (DUNE) is a wide-field space imager whose primary
goal is the study of dark energy and dark matter with unprecedented precision.
For this purpose, DUNE is optimised for the measurement of weak gravitational
lensing but will also provide complementary measurements of baryonic accoustic
oscillations, cluster counts and the Integrated Sachs Wolfe effect. Immediate
auxiliary goals concern the evolution of galaxies, to be studied with
unequalled statistical power, the detailed structure of the Milky Way and
nearby galaxies, and the demographics of Earth-mass planets. DUNE is an
Medium-class mission which makes use of readily available components, heritage
from other missions, and synergy with ground based facilities to minimise cost
and risks. The payload consists of a 1.2m telescope with a combined visible/NIR
field-of-view of 1 deg^2. DUNE will carry out an all-sky survey, ranging from
550 to 1600nm, in one visible and three NIR bands which will form a unique
legacy for astronomy. DUNE will yield major advances in a broad range of fields
in astrophysics including fundamental cosmology, galaxy evolution, and
extrasolar planet search. DUNE was recently selected by ESA as one of the
mission concepts to be studied in its Cosmic Vision programme.Comment: Accepted in Experimental Astronom
The Arecibo Galaxy Environment Survey V : The Virgo Cluster (I)
We present 21 cm observations of a 10 2 degree region in the Virgo
cluster, obtained as part of the Arecibo Galaxy Environment Survey. 289 sources
are detected over the full redshift range (-2,000 + 20,000
km/s) with 95 belonging to the cluster ( 3,000 km/s). We combine
our observations with data from the optically selected Virgo Cluster Catalogue
(VCC) and the Sloan Digital Sky Survey (SDSS). Most of our detections can be
clearly associated with a unique optical counterpart, and 30% of the cluster
detections are new objects fainter than the VCC optical completeness limit. 7
detections may have no optical counterpart and we discuss the possible origins
of these objects. 7 detections appear associated with early-type galaxies. We
perform HI stacking on the HI-undetected galaxies listed in the VCC in this
region and show that they must have significantly less gas than those actually
detected in HI. Galaxies undetected in HI in the cluster appear to be really
devoid of gas, in contrast to a sample of field galaxies from ALFALFA.Comment: 23 pages, 22 figures, 4 table
SARCS strong lensing galaxy groups: I - optical, weak lensing, and scaling laws
We present the weak lensing and optical analysis of the SL2S-ARCS (SARCS)
sample of strong lens candidates. The sample is based on the Strong Lensing
Legacy Survey (SL2S), a systematic search of strong lensing systems in the
photometric Canada-France-Hawaii Telescope Legacy Survey (CFHTLS). The SARCS
sample focuses on arc-like features and is designed to contain mostly galaxy
groups. We briefly present the weak lensing methodology that we use to estimate
the mass of the SARCS objects. Among 126 candidates, we obtain a weak lensing
detection for 89 objects with velocity dispersions of the Singular Isothermal
Sphere mass model ranging from 350 to 1000 km/s with an average value of
600km/s, corresponding to a rich galaxy group (or poor cluster). From the
galaxies belonging to the bright end of the group's red sequence (M_i<-21), we
derive the optical properties of the SARCS candidates. We obtain typical
richnesses of N=5-15 galaxies and optical luminosities of L=0.5-1.5e+12 Lsol
(within a radius of 0.5 Mpc). We use these galaxies to compute luminosity
density maps, from which a morphological classification reveals that a large
fraction of the sample are groups with a complex light distribution, either
elliptical or multimodal, suggesting that these objects are dynamically young
structures. We finally combine the lensing and optical analyses to draw a
sample of 80 most secure group candidates, i.e. weak lensing detection and
over-density at the lens position in the luminosity map, to remove false
detections and galaxy-scale systems from the initial sample. We use this
reduced sample to probe the optical scaling relations in combination with a
sample of massive galaxy clusters. We detect the expected correlations over the
probed range in mass with a typical scatter of 25% in the SIS velocity
dispersion at a given richness or luminosity, making these scaling laws
interesting mass proxie
Enhanced lensing rate by clustering of massive galaxies: newly discovered systems in the SLACS fields
[Abridged] We exploit the clustering of massive galaxies to perform a high
efficiency imaging search for gravitational lenses. Our dataset comprises 44
fields imaged by the Hubble Space Telescope (HST) Advanced Camera for Surveys
(ACS), each of which is centered on a lens discovered by the Strong Lens ACS
Survey (SLACS). We compare four different search methods: 1) automated
detection with the HST Archive Galaxy-scale Gravitational Lens Survey (HAGGLeS)
robot, 2) examining cutout images of bright galaxies (BGs) after subtraction of
a smooth galaxy light distribution, 3) examining the unsubtracted BG cutouts,
and 4) performing a full-frame visual inspection of the ACS images. We compute
purity and completeness and consider investigator time for the four algorithms,
using the main SLACS lenses as a testbed. The first and second algorithms
perform the best. We present the four new lens systems discovered during this
comprehensive search, as well as one other likely candidate. For each new lens
we use the fundamental plane to estimate the lens velocity dispersion and
predict, from the resulting lens geometry, the redshifts of the lensed sources.
Two of these new systems are found in galaxy clusters, which include the SLACS
lenses in the two respective fields. Overall we find that the enhanced lens
abundance (30^{+24}_{-8} lenses/degree^2) is higher than expected for random
fields (12^{+4}_{-2} lenses/degree^2 for the COSMOS survey). Additionally, we
find that the gravitational lenses we detect are qualitatively different from
those in the parent SLACS sample: this imaging survey is largely probing
higher-redshift, and lower-mass, early-type galaxies.Comment: submitted to ApJ; 19 pages, 12 figure
UV properties of early-type galaxies in the Virgo cluster
We study the UV properties of a volume limited sample of early-type galaxies
in the Virgo cluster combining new GALEX far- (1530 A) and near-ultraviolet
(2310 A) data with spectro-photometric data available at other wavelengths. The
sample includes 264 ellipticals, lenticulars and dwarfs spanning a large range
in luminosity (M(B)<-15). While the NUV to optical or near-IR color magnitude
relations (CMR) are similar to those observed at optical wavelengths, with a
monotonic reddening of the color index with increasing luminosity, the (FUV-V)
and (FUV-H) CMRs show a discontinuity between massive and dwarf objects. An
even more pronounced dichotomy is observed in the (FUV-NUV) CMR. For
ellipticals the (FUV-NUV) color becomes bluer with increasing luminosity and
with increasing reddening of the optical or near-IR color indices. For the
dwarfs the opposite trend is observed. These observational evidences are
consistent with the idea that the UV emission is dominated by hot, evolved
stars in giant systems, while in dwarf ellipticals residual star formation
activity is more common.Comment: 5 pages, 2 figures, 1 table. Accepted for publication in
Astrophysical Journal Letter
Deepest Near-IR Surface Photometry of Galaxies in the Local Sphere of Influence
We present near-IR, deep (4 mag deeper than 2MASS) imaging of 56 Local Volume
galaxies. Global parameters such as total magnitudes and stellar masses have
been derived and the new near-IR data combined with existing 21cm and optical
B-band data. We present multiwavelength relations such as the HI mass-to-light
ratio and investigate the maximum total baryonic mass a galaxy can have.Comment: 4 pages, 3 figures, To be published in the proceedings of "Galaxies
in the Local Volume", ed. B. Koribalski, H. Jerje
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