2,356 research outputs found
The Different Environmental Dependencies of Star-formation for Giant and Dwarf Galaxies
We examine the origins of the bimodality observed in the global properties of
galaxies around a stellar mass of 3x10^10 M_sun by comparing the environmental
dependencies of star-formation for the giant and dwarf galaxy populations. The
Sloan Digital Sky Survey DR4 spectroscopic dataset is used to produce a sample
of galaxies in the vicinity of the supercluster centered on the cluster A2199
at z=0.03 that is ~90% complete to a magnitude limit of M*+3.3. From these we
measure global trends with environment for both giant (M_r<-20 mag) and dwarf
(-19<M_r<-17.8 mag) subsamples using the luminosity-weighted mean stellar age
and H_alpha emission as independent measures of star-formation history. The
fraction of giant galaxies classed as old (t>7 Gyr) or passive (EW[H_alpha]<4
A) falls gradually from ~80% in the cluster cores to ~40% in field regions
beyond 3-4 R_virial, as found in previous studies. In contrast, we find that
the dwarf galaxy population shows a sharp transition at ~1 R_virial, from being
predominantly old/passive within the cluster, to outside where virtually all
galaxies are forming stars and old/passive galaxies are only found as
satellites to more massive galaxies. These results imply fundamental
differences in the evolution of giant and dwarf galaxies: whereas the
star-formation histories of giant galaxies are determined primarily by their
merger history, star-formation in dwarf galaxies is much more resilient to the
effects of major mergers. Instead dwarf galaxies become passive only once they
become satellites within a more massive halo, by losing their halo gas
reservoir to the host halo, or through other environment-related processes such
as galaxy harassment and/or ram-pressure stripping.Comment: 4 pages, 4 figures, accepted for publication in ApJ
Structure and Evolution of Galaxy Clusters: Internal Dynamics of ABCG 209 at z~0.21
We study the internal dynamics of the rich galaxy cluster ABGC 209 on the
basis of new spectroscopic and photometric data. The distribution in redshift
shows that ABCG 209 is a well isolated peak of 112 detected member galaxies at
z=0.209, characterised by a high value of the line-of-sight velocity
dispersion, sigma_v=1250-1400 Km/s, on the whole observed area (1 Mpc/h from
the cluster center), that leads to a virial mass of M=1.6-2.2x10^15 M_sun
within the virial radius, assuming the dynamical equilibrium. The presence of a
velocity gradient in the velocity field, the elongation in the spatial
distribution of the colour-selected likely cluster members, the elongation of
the X-ray contour levels in the Chandra image, and the elongation of cD galaxy
show that ABCG 209 is characterised by a preferential NW-SE direction. We also
find a significant deviation of the velocity distribution from a Gaussian, and
relevant evidence of substructure and dynamical segregation. All these facts
show that ABCG 209 is a strongly evolving cluster, possibly in an advanced
phase of merging.Comment: 26 pages, 14 figures. A&A in pres
Towards a Convergence of Trade and Investment Law: A Right to Take Prudential Measures for the Preservation of Financial Stability
Weak Lensing Mass Reconstruction of the Galaxy Cluster Abell 209
Weak lensing applied to deep optical images of clusters of galaxies provides
a powerful tool to reconstruct the distribution of the gravitating mass
associated to these structures. We use the shear signal extracted by an
analysis of deep exposures of a region centered around the galaxy cluster Abell
209, at redshift z=0.2, to derive both a map of the projected mass distribution
and an estimate of the total mass within a characteristic radius. We use a
series of deep archival R-band images from CFHT-12k, covering an area of 0.3
deg^2. We determine the shear of background galaxy images using a new
implementation of the modified Kaiser-Squires-Broadhurst pipeline for shear
determination, which we has been tested against the ``Shear TEsting Program 1
and 2'' simulations. We use mass aperture statistics to produce maps of the 2
dimensional density distribution, and parametric fits using both
Navarro-Frenk-White (NFW) and singular-isothermal-sphere profiles to constrain
the total mass. The projected mass distribution shows a pronounced asymmetry,
with an elongated structure extending from the SE to the NW. This is in general
agreement with the optical distribution previously found by other authors. A
similar elongation was previously detected in the X-ray emission map, and in
the distribution of galaxy colours. The circular NFW mass profile fit gives a
total mass of M_{200} = 7.7^{+4.3}_{-2.7} 10^{14} solar masses inside the
virial radius r_{200} = 1.8\pm 0.3 Mpc. The weak lensing profile reinforces the
evidence for an elongated structure of Abell 209, as previously suggested by
studies of the galaxy distribution and velocities.Comment: accepted by A&A, 15 pages, 11 figure
ACCESS - V. Dissecting ram-pressure stripping through integral-field spectroscopy and multi-band imaging
We study the case of a bright (L>L*) barred spiral galaxy from the rich
cluster A3558 in the Shapley supercluster core (z=0.05) undergoing ram-pressure
stripping. Integral-field spectroscopy, complemented by multi-band imaging,
allows us to reveal the impact of ram pressure on the interstellar medium. We
study in detail the kinematics and the physical conditions of the ionized gas
and the properties of the stellar populations. We observe one-sided extraplanar
ionized gas along the full extent of the galaxy disc. Narrow-band Halpha
imaging resolves this outflow into a complex of knots and filaments. The gas
velocity field is complex with the extraplanar gas showing signature of
rotation. In all parts of the galaxy, we find a significant contribution from
shock excitation, as well as emission powered by star formation. Shock-ionized
gas is associated with the turbulent gas outflow and highly attenuated by dust.
All these findings cover the whole phenomenology of early-stage ram-pressure
stripping. Intense, highly obscured star formation is taking place in the
nucleus, probably related to the bar, and in a region 12 kpc South-West from
the centre. In the SW region we identify a starburst characterized by a 5x
increase in the star-formation rate over the last ~100 Myr, possibly related to
the compression of the interstellar gas by the ram pressure. The scenario
suggested by the observations is supported and refined by ad hoc
N-body/hydrodynamical simulations which identify a rather narrow temporal range
for the onset of ram-pressure stripping around t~60 Myr ago, and an angle
between the galaxy rotation axis and the intra-cluster medium wind of ~45 deg.
Taking into account that the galaxy is found ~1 Mpc from the cluster centre in
a relatively low-density region, this study shows that ram-pressure stripping
still acts efficiently on massive galaxies well outside the cluster cores.Comment: 46 pages, 21 figures, accepted for publication; MNRAS 201
Numerical simulations challenged on the prediction of massive subhalo abundance in galaxy clusters: the case of Abell 2142
In this Letter we compare the abundance of member galaxies of a rich, nearby
() galaxy cluster, Abell 2142, with that of halos of comparable virial
mass extracted from sets of state-of-the-art numerical simulations, both
collisionless at different resolutions and with the inclusion of baryonic
physics in the form of cooling, star formation, and feedback by active galactic
nuclei. We also use two semi-analytical models to account for the presence of
orphan galaxies. The photometric and spectroscopic information, taken from the
Sloan Digital Sky Survey Data Release 12 (SDSS DR12) database, allows us to
estimate the stellar velocity dispersion of member galaxies of Abell 2142. This
quantity is used as proxy for the total mass of secure cluster members and is
properly compared with that of subhalos in simulations. We find that simulated
halos have a statistically significant ( sigma confidence level)
smaller amount of massive (circular velocity above )
subhalos, even before accounting for the possible incompleteness of
observations. These results corroborate the findings from a recent strong
lensing study of the Hubble Frontier Fields galaxy cluster MACS J0416
\citep{grillo2015} and suggest that the observed difference is already present
at the level of dark matter (DM) subhalos and is not solved by introducing
baryonic physics. A deeper understanding of this discrepancy between
observations and simulations will provide valuable insights into the impact of
the physical properties of DM particles and the effect of baryons on the
formation and evolution of cosmological structures.Comment: 8 pages, 2 figures. Modified to match the version published in ApJ
Shapley Supercluster Survey (ShaSS): Galaxy Evolution from Filaments to Cluster Cores
We present an overview of a multi-wavelength survey of the Shapley
supercluster (SSC; z~0.05) covering a contiguous area of 260 h^-2_70 Mpc^2
including the supercluster core. The project main aim is to quantify the
influence of cluster-scale mass assembly on galaxy evolution in one of the most
massive structures in the local Universe. The Shapley supercluster survey
(ShaSS) includes nine Abell clusters (A3552, A3554, A3556, A3558, A3559, A3560,
A3562, AS0724, AS0726) and two poor clusters (SC1327- 312, SC1329-313) showing
evidence of cluster-cluster interactions. Optical (ugri) and near-infrared (K)
imaging acquired with VST and VISTA allow us to study the galaxy population
down to m*+6 at the supercluster redshift. A dedicated spectroscopic survey
with AAOmega on the Anglo-Australian Telescope provides a magnitude-limited
sample of supercluster members with 80% completeness at ~m*+3.
We derive the galaxy density across the whole area, demonstrating that all
structures within this area are embedded in a single network of clusters,
groups and filaments. The stellar mass density in the core of the SSC is always
higher than 9E09 M_sun Mpc^-3, which is ~40x the cosmic stellar mass density
for galaxies in the local Universe. We find a new filamentary structure (~7 Mpc
long in projection) connecting the SSC core to the cluster A3559, as well as
previously unidentified density peaks. We perform a weak-lensing analysis of
the central 1 sqdeg field of the survey obtaining for the central cluster A3558
a mass of M_500=7.63E14 M_sun, in agreement with X-ray based estimates.Comment: 22 pages, 11 figures. Accepted for publication on MNRA
Discovery of a faint, star-forming, multiply lensed, Lyman-alpha blob
We report the discovery of a multiply lensed Lyman- blob (LAB) behind
the galaxy cluster AS1063 using the Multi Unit Spectroscopic Explorer (MUSE) on
the Very Large Telescope (VLT). The background source is at 3.117 and is
intrinsically faint compared to almost all previously reported LABs. We used
our highly precise strong lensing model to reconstruct the source properties,
and we find an intrinsic luminosity of =
erg s, extending to 33 kpc. We find that the LAB is associated with a
group of galaxies, and possibly a protocluster, in agreement with previous
studies that find LABs in overdensities. In addition to Lyman-
(Ly) emission, we find \ion{C}{IV}, \ion{He}{II}, and \ion{O}{III}]
ultraviolet (UV) emission lines arising from the centre of the nebula. We used
the compactness of these lines in combination with the line ratios to conclude
that the \Lya nebula is likely powered by embedded star formation. Resonant
scattering of the \Lya photons then produces the extended shape of the
emission. Thanks to the combined power of MUSE and strong gravitational
lensing, we are now able to probe the circumgalatic medium of sub-
galaxies at .Comment: 7 pages, 7 figures; moderate changes to match the accepted A&A
versoi
- …