1,021 research outputs found
Multiple merging in the Abell cluster 1367
We present a dynamical analysis of the central ~1.3 square degrees of the
cluster of galaxies Abell 1367, based on 273 redshift measurements (of which
119 are news). From the analysis of the 146 confirmed cluster members we derive
a significantly non-Gaussian velocity distribution, with a mean location C_{BI}
= 6484+/-81 km/s and a scale S_{BI} = 891+/-58 km/s. The cluster appears
elongated from the North-West to the South-East with two main density peaks
associated with two substructures. The North-West subcluster is probably in the
early phase of merging into the South-East substructure (~ 0.2 Gyr before core
crossing). A dynamical study of the two subclouds points out the existence of a
group of star-forming galaxies infalling into the core of the South-East
subcloud and suggests that two other groups are infalling into the NW and SE
subclusters respectively. These three subgroups contain a higher fraction of
star-forming galaxies than the cluster core, as expected during merging events.
Abell 1367 appears as a young cluster currently forming at the intersection of
two filaments.Comment: 15 pages, 13 figures, 7 tables. Accepted for publication on A&A. High
resolution figures at http://goldmine.mib.infn.it/papers/a1367.htm
An extragalactic HII region in the Virgo cluster
We present spectroscopic observations for six emission-line objects projected
onto the Virgo cluster. These sources have been selected from narrow band
(H\alpha+[NII]) images showing faint detectable continuum emission and EW>100
Angstrom. Five of these sources result [OIII]\lambda 5007 emitters at z ~ 0.31,
while one 122603+130724 is confirmed to be an HII region belonging to the Virgo
cluster. This point-like source has a recessional velocity of ~ 200 km/s, and
is associated with the giant galaxy VCC873 (NGC 4402). It has a higher
luminosity, star formation rate and metallicity than the extragalactic HII
region recently discovered near the Virgo galaxy VCC836 by Gerhard et al.
(2002).Comment: 7 pages, 2 figures, 4 tables. Accepted for publication on A&A. High
resolution figures and FITS images available at
http://goldmine.mib.infn.it/papers/vcc873.htm
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 origin of the mu_e - M_B and Kormendy relations in dwarf elliptical galaxies
The present work is aimed at studying the distribution of galaxies of
different types and luminosities along different structural scaling relations
to see whether massive and dwarf ellipticals have been shaped by the same
formation process. This exercise is here done by comparing the distribution of
Virgo cluster massive and dwarf ellipticals and star forming galaxies along the
B band effective surface brightness and effective radius vs. absolute magnitude
relations and the Kormendy relation to the predictions of models tracing the
effects of ram-pressure stripping on disc galaxies entering the cluster
environment and galaxy harassment. Dwarf ellipticals might have been formed
from low luminosity, late-type spirals that recently entered into the cluster
and lost their gas because of a ram-pressure stripping event, stopping their
activity of star formation. The perturbations induced by the abrupt decrease of
the star formation activity are sufficient to modify the structural properties
of disc galaxies into those of dwarf ellipticals. Galaxy harassment induce a
truncation of the disc and generally an increase of the effective surface
brightness of the perturbed galaxies. The lack of dynamical simulations of
perturbed galaxies spanning a wide range in luminosity prevents us to drive any
firm conclusion on a possible harassment-induced origin of the low surface
brightness dwarf elliptical galaxy population inhabiting the Virgo cluster.
Although the observed scaling relations are consistent with the idea that the
distribution of elliptical galaxies along the mentioned scaling relation is
just due to a gradual variation with luminosity of the Sersic index n, the
comparison with models indicates that dwarf ellipticals might have been formed
by a totally different process than giant ellipticalsComment: Accepted for publication on A&
The effect of the environment on the HI scaling relations
We use a volume-, magnitude-limited sample of nearby galaxies to investigate
the effect of the environment on the HI scaling relations. We confirm that the
HI-to-stellar mass ratio anti correlates with stellar mass, stellar mass
surface density and NUV-r colour across the whole range of parameters covered
by our sample (10^9 <M*<10^11 Msol, 7.5 <mu*<9.5 Msol kpc^-2, 2<NUV-r<6 mag).
These scaling relations are also followed by galaxies in the Virgo cluster,
although they are significantly offset towards lower gas content.
Interestingly, the difference between field and cluster galaxies gradually
decreases moving towards massive, bulge-dominated systems. By comparing our
data with the predictions of chemo-spectrophotometric models of galaxy
evolution, we show that starvation alone cannot explain the low gas content of
Virgo spirals and that only ram-pressure stripping is able to reproduce our
findings. Finally, motivated by previous studies, we investigate the use of a
plane obtained from the relations between the HI-to-stellar mass ratio, stellar
mass surface density and NUV-r colour as a proxy for the HI deficiency
parameter. We show that the distance from the `HI gas fraction plane' can be
used as an alternative estimate for the HI deficiency, but only if carefully
calibrated on pre-defined samples of `unperturbed' systems.Comment: Accepted for publication on MNRAS main journal. 11 pages, 6 figures,
1 tabl
The Sloan Lens ACS Survey. IX. Colors, Lensing and Stellar Masses of Early-type Galaxies
We present the current photometric dataset for the Sloan Lens ACS (SLACS)
Survey, including HST photometry from ACS, WFPC2, and NICMOS. These data have
enabled the confirmation of an additional 15 grade `A' (certain) lens systems,
bringing the number of SLACS grade `A' lenses to 85; including 13 grade `B'
(likely) systems, SLACS has identified nearly 100 lenses and lens candidates.
Approximately 80% of the grade `A' systems have elliptical morphologies while
~10% show spiral structure; the remaining lenses have lenticular morphologies.
Spectroscopic redshifts for the lens and source are available for every system,
making SLACS the largest homogeneous dataset of galaxy-scale lenses to date. We
have developed a novel Bayesian stellar population analysis code to determine
robust stellar masses with accurate error estimates. We apply this code to
deep, high-resolution HST imaging and determine stellar masses with typical
statistical errors of 0.1 dex; we find that these stellar masses are unbiased
compared to estimates obtained using SDSS photometry, provided that informative
priors are used. The stellar masses range from 10^10.5 to 10^11.8 M and
the typical stellar mass fraction within the Einstein radius is 0.4, assuming a
Chabrier IMF. The ensemble properties of the SLACS lens galaxies, e.g. stellar
masses and projected ellipticities, appear to be indistinguishable from other
SDSS galaxies with similar stellar velocity dispersions. This further supports
that SLACS lenses are representative of the overall population of massive
early-type galaxies with M* >~ 10^11 M, and are therefore an ideal
dataset to investigate the kpc-scale distribution of luminous and dark matter
in galaxies out to z ~ 0.5.Comment: 20 pages, 18 figures, 5 tables, published in Ap
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
Resolved stellar mass maps of galaxies. I: method and implications for global mass estimates
(Abridged) We introduce a novel technique to construct spatially resolved
maps of stellar mass surface density in galaxies based on optical and near IR
imaging. We use optical/NIR colour(s) to infer effective stellar mass-to-light
ratios (M/L) at each pixel, which are then multiplied by the surface brightness
to obtain the local stellar surface mass density. We build look-up tables to
express M/L as a function of colour(s) by marginalizing over a Monte Carlo
library of 50,000 stellar population synthesis (SPS) models by Charlot &
Bruzual (2007), which include a revised prescription for the TP-AGB stellar
evolutionary phase, with a wide range of dust exinctions. In order to extract
reliable flux and colour information at any position in the galaxy, we perform
a median adaptive smoothing of the images that preserves the highest possible
spatial resolution. As the most practical and robust, and hence fiducial
method, we express the M/L in the H band as a function of (g-i) and (i-H).
Stellar mass maps computed in this way have a typical accuracy of 30 per cent
or less at any given pixel, determined from the scatter in the models. We
compare maps obtained with our fiducial method with those derived using other
combinations of bandpasses and the old BC03 TP-AGB prescription. Finally, we
compare total stellar mass estimates obtained by integrating resolved mass maps
with those obtained with unresolved photometry. In galaxies with evident dust
lanes, unresolved estimates may miss up to 40 per cent of the total stellar
mass because dusty regions are strongly under-represented in the luminous
fluxes.Comment: Accepted for publication on MNRAS on Aug 10th 2009. 21 pages, 14
figures (see http://www.mpia.de/homes/zibetti/mass_maps_I.pdf for full
resolution). One appendix added and minor changes done wrt to original
submissio
1.65 micrometers (H-band) surface photometry of galaxies. III: observations of 558 galaxies with the TIRGO 1.5m telescope
We present near-infrared H-band (1.65 micron) surface photometry of 558
galaxies in the Coma Supercluster and in the Virgo cluster. This data set,
obtained with the Arcetri NICMOS3 camera ARNICA mounted on the Gornergrat
Infrared Telescope, is aimed at complementing, with observations of mostly
early-type objects, our NIR survey of spiral galaxies in these regions,
presented in previous papers of this series. Magnitudes at the optical radius,
total magnitudes, isophotal radii and light concentration indices are derived.
We confirm the existence of a positive correlation between the near-infrared
concentration index and the galaxy H-band luminosity. (Tables 1 and 2 are only
available in electronic form upon request to [email protected])Comment: 12 pages, 6 figures. Accepted for publication in A&A
The detection and photometric redshift determination of distant galaxies using SIRTF's Infrared Array Camera
We investigate the ability of the Space Infrared Telescope Facility's
Infrared Array Camera to detect distant (z ~ 3)galaxies and measure their
photometric redshifts. Our analysis shows that changing the original long
wavelength filter specifications provides significant improvements in
performance in this and other areas.Comment: 28 pages incl 12 figures; to appear in June 1999 PASP. Fig.12
replaced with corrected versio
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