2,513 research outputs found
The VIMOS VLT Deep Survey. The different assembly history of passive and star-forming L_B >= L*_B galaxies in the group environment at z < 1
We use the VIMOS VLT Deep Survey to study the close environment of galaxies
in groups at 0.2 = L*_B galaxies (Me_B =
M_B + 1.1z <= -20) are identified with Me_B <= -18.25 and within a relative
distance 5h^-1 kpc <= rp <= 100h^-1 kpc and relative velocity Delta v <= 500
km/s . The richness N of a group is defined as the number of Me_B <= -18.25
galaxies belonging to that group. We split our principal sample into red,
passive galaxies with NUV - r >= 4.25 and blue, star-forming galaxies with NUV
- r < 4.25. We find that blue galaxies with a close companion are primarily
located in poor groups, while the red ones are in rich groups. The number of
close neighbours per red galaxy increases with N, with n_red being proportional
to 0.11N, while that of blue galaxies does not depend on N and is roughly
constant. In addition, these trends are found to be independent of redshift,
and only the average n_blue evolves, decreasing with cosmic time. Our results
support the following assembly history of L_B >= L*_B galaxies in the group
environment: red, massive galaxies were formed in or accreted by the dark
matter halo of the group at early times (z >= 1), therefore their number of
neighbours provides a fossil record of the stellar mass assembly of groups,
traced by their richness N. On the other hand, blue, less massive galaxies have
recently been accreted by the group potential and are still in their parent
dark matter halo, having the same number of neighbours irrespective of N. As
time goes by, these blue galaxies settle in the group potential and turn red
and/or fainter, thus becoming satellite galaxies in the group. With a toy
quenching model, we estimate an infall rate of field galaxies into the group
environment of R_infall = 0.9 - 1.5 x 10^-4 Mpc^-3 Gyr^-1 at z ~ 0.7.Comment: Astronomy and Astrophysics, in press. 11 pages, 11 figures, 4 tables.
Minor changes with respect to the first versio
Influence of curing thermal history on cross-linking degree of a polydimethylsiloxane: Swelling and mechanical analyses
In this work, the change of the elastic properties induced by a change in cross-linking conditions of polydimethylsiloxane is investigated by measuring its shear modulus by dynamic mechanical analysis and correlating it to that predicted
from swelling measurements. Polymer cross-linking is performed at different curing temperatures reached with ramps at different heating rates. From both mechanical and swelling measurements, the molecular weight between cross-links, MC, is determined, and its dependency on the applied thermal history is analyzed. The main results are: (i) the elastic modulus of the cured material is not significantly affected by the heating rate adopted, while (ii) the curing temperature has a significant influence on the polydimethylsiloxane mechanical properties. In addition, (iii) MC evaluation from swelling measurements is in good agreement with that estimated from mechanical measurements when appropriate theories are considered. This last result suggests that swelling experiments can be considered as a reliable tool to predict the elastic modulus of the polydimethylsiloxane studied. The quantitative information reported in this paper, also obtainable by the suggested method if other thermal curing histories are applied, is extremely useful for the proper design of devices based on polydimethylsiloxane
Excavation at Aguas Buenas, Robinson Crusoe Island, Chile, of a gunpowder magazine and the supposed campsite of Alexander Selkirk, together with an account of early navigational dividers
Excavations were undertaken of a ruined building at Aguas Buenas, identified as an 18th-century Spanish gunpowder magazine. Evidence was also found for the campsite of an early European occupant of the island. A case is made that this was Alexander Selkirk, a castaway here from 1704 to 1709. Selkirk was the model for Defoe’s Robinson Crusoe. A detailed discussion is given of a fragment of copper alloy identifi ed as being from a pair of navigational dividers
Evidence of Substructure in the Cluster of Galaxies A3558
We investigate the dynamical properties of the cluster of galaxies A3558
(Shapley 8). Studying a region of one square degree ( 3 Mpc) centered
on the cluster cD galaxy, we have obtained a statistically complete photometric
catalog with positions and magnitudes of 1421 galaxies (down to a limiting
magnitude of ). This catalog has been matched to the recent velocity
data obtained by Mazure et al. (1997) and from the literature, yielding a
radial velocity catalog containing 322 galaxies. Our analysis shows that the
position/velocity space distribution of galaxies shows significant
substructure. A central bimodal core detected previously in preliminary studies
is confirmed by using the Adaptive Kernel Technique and Wavelet Analysis. We
show that this central bimodal subtructure is nevertheless composed of a
projected feature, kinematically unrelated to the cluster, plus a group of
galaxies probably in its initial merging phase into a relaxed core. The cD
velocity offset with respect to the average cluster redshift, reported earlier
by several authors, is completely eliminated as a result of our dynamical
analysis. The untangling of the relaxed core component also allows a better,
more reliable determination of the central velocity dispersion, which in turn
eliminates the ``-problem'' for A3558. The cluster also shows a
``preferential'' distribution of subclumps coinciding with the direction of the
major axis position angle of the cD galaxy and of the central X-ray emission
ellipsoidal distribution, in agreement with an anisotropic merger scenario.Comment: 35 pages in latex, 17 figures in Postscript, accepted for publication
in the Astrophysical Journa
The VIMOS Ultra Deep Survey. Luminosity and stellar mass dependence of galaxy clustering at z~3
We present the study of the dependence of galaxy clustering on luminosity and
stellar mass in the redshift range 2z3.5 using 3236 galaxies with robust
spectroscopic redshifts from the VIMOS Ultra Deep Survey (VUDS). We measure the
two-point real-space correlation function for four volume-limited
stellar mass and four luminosity, M absolute magnitude selected,
sub-samples. We find that the scale dependent clustering amplitude
significantly increases with increasing luminosity and stellar mass indicating
a strong galaxy clustering dependence on these properties. This corresponds to
a strong relative bias between these two sub-samples of b/b=0.43.
Fitting a 5-parameter HOD model we find that the most luminous and massive
galaxies occupy the most massive dark matter haloes with
M = 10 h M. Similar to the
trends observed at lower redshift, the minimum halo mass M depends on
the luminosity and stellar mass of galaxies and grows from M
=10 hM to M=10 hM
from the faintest to the brightest among our galaxy sample, respectively. We
find the difference between these halo masses to be much more pronounced than
is observed for local galaxies of similar properties. Moreover, at z~3, we
observe that the masses at which a halo hosts, on average, one satellite and
one central galaxy is M4M over all luminosity ranges,
significantly lower than observed at z~0 indicating that the halo satellite
occupation increases with redshift. The luminosity and stellar mass dependence
is also reflected in the measurements of the large scale galaxy bias, which we
model as b(L)=1.92+25.36(L/L). We conclude our study
with measurements of the stellar-to-halo mass ratio (SHMR).Comment: 20 pages, 11 figures, A&A in press, v2. revised discussion in sec.
5.5, changed Fig. 4 and Fig. 11, added reference
Next Generation Cosmology: Constraints from the Euclid Galaxy Cluster Survey
We study the characteristics of the galaxy cluster samples expected from the
European Space Agency's Euclid satellite and forecast constraints on
cosmological parameters describing a variety of cosmological models. The method
used in this paper, based on the Fisher Matrix approach, is the same one used
to provide the constraints presented in the Euclid Red Book (Laureijs et
al.2011). We describe the analytical approach to compute the selection function
of the photometric and spectroscopic cluster surveys. Based on the photometric
selection function, we forecast the constraints on a number of cosmological
parameter sets corresponding to different extensions of the standard LambdaCDM
model. The dynamical evolution of dark energy will be constrained to Delta
w_0=0.03 and Delta w_a=0.2 with free curvature Omega_k, resulting in a
(w_0,w_a) Figure of Merit (FoM) of 291. Including the Planck CMB covariance
matrix improves the constraints to Delta w_0=0.02, Delta w_a=0.07 and a
FoM=802. The amplitude of primordial non-Gaussianity, parametrised by f_NL,
will be constrained to \Delta f_NL ~ 6.6 for the local shape scenario, from
Euclid clusters alone. Using only Euclid clusters, the growth factor parameter
\gamma, which signals deviations from GR, will be constrained to Delta
\gamma=0.02, and the neutrino density parameter to Delta Omega_\nu=0.0013 (or
Delta \sum m_\nu=0.01). We emphasise that knowledge of the observable--mass
scaling relation will be crucial to constrain cosmological parameters from a
cluster catalogue. The Euclid mission will have a clear advantage in this
respect, thanks to its imaging and spectroscopic capabilities that will enable
internal mass calibration from weak lensing and the dynamics of cluster
galaxies. This information will be further complemented by wide-area
multi-wavelength external cluster surveys that will already be available when
Euclid flies. [Abridged]Comment: submitted to MNRA
Spectroscopic confirmation of clusters from the ESO imaging survey
We measure redshifts for 67 galaxies in the field of six cluster candidates
from the ESO Imaging Survey (EIS). The cluster candidates are selected in the
EIS patches C and D among those with estimated mean redshifts between 0.5 and
0.7. The observations were made with EFOSC2 at the 3.6m ESO telescope.
In the six candidate cluster fields, we identify 19 possible sets of 2 to 7
galaxies in redshift space. In order to establish which of the 19 sets are
likely to correspond to real dense systems we compare our counts with those
expected from a uniform distribution of galaxies with given luminosity
function. In order to take into account the effect of the Large Scale
Structure, we modulate the probability computed from the luminosity function
with random samplings of the Canada-France Redshift Survey.
We find that four out of six candidate EIS clusters are likely to correspond
to real systems in redshift space (> 95 % confidence level). Two of these
systems have mean redshift in agreement with the redshift estimate given by the
matched filter algorithm. The other two systems have significantly lower
redshifts.
We discuss the implications of our results in the context of our ongoing
research projects aimed at defining high-redshift optically-selected cluster
samples.Comment: To appear in A&A, main journal -- 12 pages, 9 figure
Novel strategies for the treatment of myelofibrosis driven by recent advances in understanding the role of the microenvironment in its etiology
Myelofibrosis is the advanced stage of the Philadelphia chromosome-negative myeloproliferative neoplasms (MPNs), characterized by systemic inflammation, hematopoietic failure in the bone marrow, and development of extramedullary hematopoiesis, mainly in the spleen. The only potentially curative therapy for this disease is hematopoietic stem cell transplantation, an option that may be offered only to those patients with a compatible donor and with an age and functional status that may face its toxicity. By contrast, with the Philadelphia-positive MPNs that can be dramatically modified by inhibitors of the novel BCR-ABL fusion-protein generated by its genetic lesion, the identification of the molecular lesions that lead to the development of myelofibrosis has not yet translated into a treatment that can modify the natural history of the disease. Therefore, the cure of myelofibrosis remains an unmet clinical need. However, the excitement raised by the discovery of the genetic lesions has inspired additional studies aimed at elucidating the mechanisms driving these neoplasms towards their final stage. These studies have generated the feeling that the cure of myelofibrosis will require targeting both the malignant stem cell clone and its supportive microenvironment. We will summarize here some of the biochemical alterations recently identified in MPNs and the novel therapeutic approaches currently under investigation inspired by these discoveries
Suppressed radio emission in supercluster galaxies: enhanced ram pressure in merging clusters?
The environmental influence on the 1.4 GHz continuum radio emission of
galaxies is analyzed in a 600 deg2 region of the local Universe containing the
Shapley Supercluster (SSC). Galaxies in the FLASH and 6dFGS redshift surveys
are cross-identified with NVSS radio sources, selected in a subsample doubly
complete in volume and luminosity. Environmental effects are studied through a
smoothed density field (normalized with random catalogs with the same survey
edges and redshift selection function) and the distance to the nearest cluster
(R/r200, where r200 is the virial radius, whose relation to the aperture
velocity dispersion is quantified). The fraction of high radio loudness
(R_K=L_radio/L_K) galaxies in the 10 Mpc Abell 3558 cluster complex at the core
of the SSC (SSC-CR) is half as large than elsewhere. In the SSC-CR, R_K is
anti-correlated with the density of the large-scale environment and correlated
with R/r200: central brightest cluster galaxies (BCGs) in the SSC-CR are 10x
less radio-loud than BCGs elsewhere, with signs of suppressed radio loudness in
the SSC-CR also present beyond the BCGs, out to at least 0.3 r200. This
correlation is nearly as strong as the tight correlation of L_K with R/r200
(K-luminosity segregation), inside the SSC-CR. The suppression of radio
loudness in SSC-CR BCGs can be attributed to cluster-cluster mergers that
destroy the cool core and thus the supply of gas to the central AGN. We
analytically demonstrate that the low radio loudness of non-BCG galaxies within
SSC-CR clusters cannot be explained by direct major galaxy mergers or rapid
galaxy flyby collisions, but by the loss of gas supply through the enhanced ram
pressure felt when these galaxies cross the shock front between the 2 merging
clusters and are later subjected to the stronger wind from the 2nd cluster.Comment: Version consolidated with Erratum A&A 499, 4
Cosmic dance in the Shapley Concentration Core - I. A study of the radio emission of the BCGs and tailed radio galaxies
The Shapley Concentration () covers several degrees in the
Southern Hemisphere, and includes galaxy clusters in advanced evolutionary
stage, groups of clusters in the early stages of merger, fairly massive
clusters with ongoing accretion activity, and smaller groups located in
filaments in the regions between the main clusters. With the goal to
investigate the role of cluster mergers and accretion on the radio galaxy
population, we performed a multi-wavelength study of the BCGs and of the
galaxies showing extended radio emission in the cluster complexes of Abell 3528
and Abell 3558. Our study is based on a sample of 12 galaxies. We observed the
clusters with the GMRT at 235, 325 and 610 MHz, and with the VLA at 8.46 GHz.
We complemented our study with the TGSS at 150 MHz, the SUMSS at 843 MHz and
ATCA at 1380, 1400, 2380, and 4790 MHz data. Optical imaging with ESO-VST and
mid-IR coverage with WISE are also available for the host galaxies. We found
deep differences in the properties of the radio emission of the BCGs in the two
cluster complexes. The BCGs in the A3528 complex and in A3556, which are
relaxed cool-core objects, are powerful active radio galaxies. They also
present hints of restarted activity. On the contrary, the BCGs in A3558 and
A3562, which are well known merging systems, are very faint, or quiet, in the
radio band. The optical and IR properties of the galaxies are fairly similar in
the two complexes, showing all passive red galaxies. Our study shows remarkable
differences in the radio properties of the BGCs, which we relate to the
different dynamical state of the host cluster. On the contrary, the lack of
changes between such different environments in the optical band suggests that
the dynamical state of galaxy clusters does not affect the optical counterparts
of the radio galaxies, at least over the life-time of the radio emission.Comment: 24 pages, 11 figures, accepted for publication in Astronomy &
Astrophysic
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