39 research outputs found
The Grism lens-amplified survey from space (GLASS). VIII. The influence of the cluster properties on Halpha emitter galaxies at 0.3<z<0.7
Exploiting the data of the Grism Lens-Amplified Survey from Space (GLASS), we
characterize the spatial distribution of star formation in 76 high star forming
galaxies in 10 clusters at 0.3< z <0.7. All these galaxies are likely
restricted to first infall. In a companion paper we contrast the properties of
field and cluster galaxies, whereas here we correlate the properties of
H{\alpha} emitters to a number of tracers of the cluster environment to
investigate its role in driving galaxy transformations. H{\alpha} emitters are
found in the clusters out to 0.5 virial radii, the maximum radius covered by
GLASS. The peak of the H{\alpha} emission is offset with respect to the peak of
the UV-continuum. We decompose this offsets into a radial and tangential
component. The radial compo- nent points away from the cluster center in 60% of
the cases, with 95% confidence. The decompositions agree with cosmological
simulations, i.e. the H{\alpha} emission offset correlates with galaxy velocity
and ram-pressure stripping signatures. Trends between H{\alpha} emitter
properties and surface mass density distributions and X-ray emissions emerge
only for unrelaxed clusters. The lack of strong correlations with the global
environment does not allow us to identify a unique environmental effect
originating from the cluster center. In contrast, correla- tions between
H{\alpha} morphology and local number density emerge. We conclude that local
effects, uncorrelated to the cluster-centric radius, play a more important role
in shaping galaxy properties.Comment: ApJ in press (16 pages, 8 figures
The Grism Lens-Amplified Survey from Space (GLASS). V. Extent and spatial distribution of star formation in z~0.5 cluster galaxies
We present the first study of the spatial distribution of star formation in
z~0.5 cluster galaxies. The analysis is based on data taken with the Wide Field
Camera 3 as part of the Grism Lens-Amplified Survey from Space (GLASS). We
illustrate the methodology by focusing on two clusters (MACS0717.5+3745 and
MACS1423.8+2404) with different morphologies (one relaxed and one merging) and
use foreground and background galaxies as field control sample. The
cluster+field sample consists of 42 galaxies with stellar masses in the range
10^8-10^11 M_sun, and star formation rates in the range 1-20 M_sun/yr. Both in
clusters and in the field, H{\alpha} is more extended than the rest-frame UV
continuum in 60% of the cases, consistent with diffuse star formation and
inside out growth. In ~20% of the cases, the H{\alpha} emission appears more
extended in cluster galaxies than in the field, pointing perhaps to ionized gas
being stripped and/or star formation being enhanced at large radii. The peak of
the H{\alpha} emission and that of the continuum are offset by less than 1 kpc.
We investigate trends with the hot gas density as traced by the X-ray emission,
and with the surface mass density as inferred from gravitational lens models
and find no conclusive results. The diversity of morphologies and sizes
observed in H_alpha illustrates the complexity of the environmental process
that regulate star formation. Upcoming analysis of the full GLASS dataset will
increase our sample size by almost an order of magnitude, verifying and
strengthening the inference from this initial dataset.Comment: 18 pages, 15 figures, accepted for publication in Ap
The evolution of the density of galaxy clusters and groups: denser environments at higher redshifts
We show that, observationally, the projected local density distribution in
high-z clusters is shifted towards higher values compared to clusters at lower
redshift. To search for the origin of this evolution, we analyze a sample of
haloes selected from the Millennium Simulation and populated using
semi-analytic models, investigating the relation between observed projected
density and physical 3D density, using densities computed from the 10 and 3
closest neighbours. Both observationally and in the simulations, we study the
relation between number of cluster members and cluster mass, and number of
members per unit of cluster mass. We find that the observed evolution of
projected densities reflects a shift to higher values of the physical 3D
density distribution. In turn, this must be related with the globally higher
number of galaxies per unit of cluster volume N/V in the past. We show that the
evolution of N/V is due to a combination of two effects: a) distant clusters
were denser in dark matter (DM) simply because the DM density within R_{200}
(~the cluster virial radius) is defined to be a fixed multiple of the critical
density of the Universe, and b) the number of galaxies per unit of cluster DM
mass is remarkably constant both with redshift and cluster mass if counting
galaxies brighter than a passively evolving magnitude limit. Our results
highlight that distant clusters were much denser environments than today's
clusters, both in galaxy number and mass, and that the density conditions felt
by galaxies in virialized systems do not depend on the system mass.Comment: accepted for publication in MNRA
Cluster Galaxies Die Hard
We investigate how the specific star formation rates of galaxies of different
masses depend on cluster-centric radius and on the central/satellite dichotomy
in both field and cluster environments. Recent data from a variety of sources,
including the cluster catalogue of von der Linden et al. are compared to the
semi-analytic models of De Lucia & Blaizot. We find that these models predict
too many passive satellite galaxies in clusters, too few passive central
galaxies with low stellar masses, and too many passive central galaxies with
high masses. We then outline a series of modifications to the model necessary
to solve these problems: a) Instead of instantaneous stripping of the external
gas reservoir after a galaxy becomes a satellite, the gas supply is assumed to
decrease at the same rate that the surrounding halo loses mass due to tidal
stripping, b) The AGN feedback efficiency is lowered to bring the fraction of
massive passive centrals in better agreement with the data. We also allow for
radio mode AGN feedback in satellite galaxies. c) We assume that satellite
galaxies residing in host haloes with masses below 10^12 M_sun do not undergo
any stripping. We highlight the fact that in low mass galaxies, the external
reservoir is composed primarily of gas that has been expelled from the galactic
disk by supernovae driven winds. This gas must remain available as a future
reservoir for star formation, even in satellite galaxies. Finally, we present a
simple recipe for the stripping of gas and dark matter in satellites that can
be used in models where subhalo evolution is not followed in detail.Comment: Models of ram-pressure stripping and some extra discussion added,
references added. Conclusions unchanged. 20 pages, 15 figures. Accepted for
publication in MNRAS
Multiple Images of a Highly Magnified Supernova Formed by an Early-Type Cluster Galaxy Lens
In 1964, Refsdal hypothesized that a supernova whose light traversed multiple
paths around a strong gravitational lens could be used to measure the rate of
cosmic expansion. We report the discovery of such a system. In Hubble Space
Telescope imaging, we have found four images of a single supernova forming an
Einstein cross configuration around a redshift z=0.54 elliptical galaxy in the
MACS J1149.6+2223 cluster. The cluster's gravitational potential also creates
multiple images of the z=1.49 spiral supernova host galaxy, and a future
appearance of the supernova elsewhere in the cluster field is expected. The
magnifications and staggered arrivals of the supernova images probe the cosmic
expansion rate, as well as the distribution of matter in the galaxy and cluster
lenses.Comment: Published in the 6 March 2015 issue of Science; 17 pages, 7 figures,
and 3 tables including Supplementary Material
PAX2 Regulates ADAM10 Expression and Mediates Anchorage-Independent Cell Growth of Melanoma Cells
PAX transcription factors play an important role during development and carcinogenesis. In this study, we investigated PAX2 protein levels in melanocytes and melanoma cells by Western Blot and immunofluorescence analysis and characterized the role of PAX2 in the pathogenesis of melanoma. In vitro we found weak PAX2 protein expression in keratinocytes and melanocytes. Compared to melanocytes increased PAX2 protein levels were detectable in melanoma cell lines. Interestingly, in tissue sections of melanoma patients nuclear PAX2 expression strongly correlated with nuclear atypia and the degree of prominent nucleoli, indicating an association of PAX2 with a more atypical cellular phenotype. In addition, with chromatin immunoprecipitation assay, PAX2 overexpression and PAX2 siRNA we present compelling evidence that PAX2 can regulate ADAM10 expression, a metalloproteinase known to play important roles in melanoma metastasis. In human tissue samples we found co-expression of PAX2 and ADAM10 in melanocytes of benign nevi and in melanoma cells of patients with malignant melanoma. Importantly, the downregulation of PAX2 by specific siRNA inhibited the anchorage independent cell growth and decreased the migratory and invasive capacity of melanoma cells. Furthermore, the downregulation of PAX2 abrogated the chemoresistance of melanoma cells against cisplatin, indicating that PAX2 expression mediates cell survival and plays important roles during melanoma progression
The Rest-Frame Optical Luminosity Function of Cluster Galaxies at z<0.8 and the Assembly of the Cluster Red Sequence
We present the rest-frame optical luminosity function (LF) of red sequence
galaxies in 16 clusters at 0.4<z<0.8 drawn from the ESO Distant Cluster Survey
(EDisCS). We compare our clusters to an analogous sample from the Sloan Digital
Sky Survey (SDSS) and match the EDisCS clusters to their most likely
descendants. We measure all LFs down to M M* + (2.5 - 3.5). At z<0.8, the
bright end of the LF is consistent with passive evolution but there is a
significant build-up of the faint end of the red sequence towards lower
redshift. There is a weak dependence of the LF on cluster velocity dispersion
for EDisCS but no such dependence for the SDSS clusters. We find tentative
evidence that red sequence galaxies brighter than a threshold magnitude are
already in place, and that this threshold evolves to fainter magnitudes toward
lower redshifts. We compare the EDisCS LFs with the LF of co-eval red sequence
galaxies in the field and find that the bright end of the LFs agree. However,
relative to the number of bright red galaxies, the field has more faint red
galaxies than clusters at 0.6<z<0.8 but fewer at 0.4<z<0.6, implying
differential evolution. We compare the total light in the EDisCS cluster red
sequences to the total red sequence light in our SDSS cluster sample. Clusters
at 0.4<z<0.8 must increase their luminosity on the red sequence (and therefore
stellar mass in red galaxies) by a factor of 1-3 by z=0. The necessary
processes that add mass to the red sequence in clusters predict local clusters
that are over-luminous as compared to those observed in the SDSS. The predicted
cluster luminosities can be reconciled with observed local cluster luminosities
by combining multiple previously known effects.Comment: Accepted for publication in the Astrophysical Journal. 36 pages, 16
figures, 10 table