134 research outputs found
LoCuSS: Exploring the selection of faint blue background galaxies for cluster weak-lensing
Cosmological constraints from galaxy clusters rely on accurate measurements
of the mass and internal structure of clusters. An important source of
systematic uncertainty in cluster mass and structure measurements is the secure
selection of background galaxies that are gravitationally lensed by clusters.
This issue has been shown to be particular severe for faint blue galaxies. We
therefore explore the selection of faint blue background galaxies, by reference
to photometric redshift catalogs derived from the COSMOS survey and our own
observations of massive galaxy clusters at z~0.2. We show that methods relying
on photometric redshifts of galaxies in/behind clusters based on observations
through five filters, and on deep 30-band COSMOS photometric redshifts are both
inadequate to identify safely faint blue background galaxies. This is due to
the small number of filters used by the former, and absence of massive galaxy
clusters at redshifts of interest in the latter. We therefore develop a
pragmatic method to combine both sets of photometric redshifts to select a
population of blue galaxies based purely on photometric analysis. This sample
yields stacked weak-lensing results consistent with our previously published
results based on red galaxies. We also show that the stacked clustercentric
number density profile of these faint blue galaxies is consistent with
expectations from consideration of the lens magnification signal of the
clusters. Indeed, the observed number density of blue background galaxies
changes by ~10-30 per cent across the radial range over which other surveys
assume it to be flat.Comment: submitted to MNRA
LoCuSS: The Near-Infrared Luminosity and Weak-Lensing Mass Scaling Relation of Galaxy Clusters
We present the first scaling relation between weak-lensing galaxy cluster
mass, , and near-infrared luminosity, . Our results are based on
17 clusters observed with wide-field instruments on Subaru, the United Kingdom
Infrared Telescope, the Mayall Telescope, and the MMT. We concentrate on the
relation between projected 2D weak-lensing mass and spectroscopically confirmed
luminosity within 1Mpc, modelled as , obtaining a power
law slope of and an intrinsic scatter of
. Intrinsic scatter of ~10% is a
consistent feature of our results regardless of how we modify our approach to
measuring the relationship between mass and light. For example, deprojecting
the mass and measuring both quantities within , that is itself
obtained from the lensing analysis, yields
and . We also
find that selecting members based on their (J-K) colours instead of
spectroscopic redshifts neither increases the scatter nor modifies the slope.
Overall our results indicate that near-infrared luminosity measured on scales
comparable with (typically 1Mpc for our sample) is a low scatter and
relatively inexpensive proxy for weak-lensing mass. Near-infrared luminosity
may therefore be a useful mass proxy for cluster cosmology experiments.Comment: 9 Pages, 5 Figures, 3 Tables. Submitted to MNRA
The evolution of dwarf galaxies in the Coma supercluster
We employ spectroscopic and photometric data from SDSS DR7, in a 500 sq
degree region, to understand the evolution of dwarf (~M*+2<M_z<M*+4) galaxies
in the Coma supercluster (z=0.023). We show that in the Coma supercluster, the
red dwarfs are mostly concentrated in the dense cores of the Coma and Abell
1367 clusters, and in the galaxy groups embedded in the filament connecting
them. The post-starburst (k+A) dwarfs however are found in the infall regions
of the Coma and Abell 1367 clusters, and occasionally in galaxy groups embedded
along the filament, suggesting that strong velocity fields prevalent in the
vicinity of deep potential wells may be closely related to the mechanism(s)
leading to the post-starburst phase in dwarf galaxies. Moreover, the blue
colour of some k+A dwarfs in the Coma cluster, found within its virial radius,
suggests that the star formation in these galaxies was quenched very rapidly in
the last 500 Myr. More than 60% of all red dwarf galaxies in the supercluster
have 0-3 ang of H_\delta in absorption, which suggests that a major episode of
star formation occurred in a non-negligible fraction of these galaxies, ending
within the last Gyr, allowing them to move to the red sequence. The
distribution of the blue dwarf galaxies in the Coma supercluster is bimodal in
the EW(H_\alpha)-EW(H_\delta) plane, with one population having very high
emission in H_\alpha, and some emission in H_\delta. A sub-population of blue
dwarfs is coincident with the red dwarfs in the EW(H_\alpha)-EW(H_\delta)
plane, showing absorption in H_\delta and relatively lower emission in
H_\alpha. We suggest that a large fraction of the latter population are the
progenitors of the passive dwarf galaxies that are abundantly found in the
cores of low-redshift rich clusters such as Coma.Comment: 6 Pages, 5 Figures, Accepted for publication in MNRA
LoCuSS : The Splashback Radius of Massive Galaxy Clusters and Its Dependence on Cluster Merger History
We present the direct detection of the splashback feature using the sample of massive galaxy clusters from the Local Cluster Substructure Survey (LoCuSS). This feature is clearly detected (above 5 sigma) in the stacked luminosity density profile obtained using the K-band magnitudes of spectroscopically confirmed cluster members. We obtained the best-fit model by means of Bayesian inference, which ranked models including the splashback feature as more descriptive of the data with respect to models that do not allow for this transition. In addition, we have assessed the impact of the cluster dynamical state on the occurrence of the splashback feature. We exploited the extensive multiwavelength LoCuSS data set to test a wide range of proxies for the cluster formation history, finding the most significant dependence of the splashback feature location and scale according to the presence or absence of X-ray emitting galaxy groups in the cluster infall regions. In particular, we report for the first time that clusters that do not show massive infalling groups present the splashback feature at a smaller clustercentric radius r (sp)/r (200,m ) = 1.158 +/- 0.071 than clusters that are actively accreting groups r (sp)/r (200,m ) = 1.291 +/- 0.062. The difference between these two subsamples is significant at 4.2 sigma, suggesting a correlation between the properties of the cluster potential and its accretion rate and merger history. Similarly, clusters that are classified as old and dynamically inactive present stronger signatures of the splashback feature, with respect to younger, more active clusters. We are directly observing how fundamental dynamical properties of clusters reverberate across vastly different physical scales.Peer reviewe
Star formation, starbursts and quenching across the Coma supercluster
We analyse Spitzer MIPS 24micron observations, and SDSS (DR7) optical
broadband photometry and spectra, to investigate the star formation (SF)
properties of galaxies residing in the Coma supercluster region. We find that
SF in dwarf galaxies is quenched only in the high density environment at the
centre of clusters and groups, but passively-evolving massive galaxies are
found in all environments, indicating that massive galaxies can become passive
via internal processes. We find AGN activity is suppressed in the cluster
cores. We present evidence for a strong dependence of the mechanism(s)
responsible for quenching SF in dwarf galaxies on the cluster potential. We
find a significant increase in the mean EW of Halpha among star-forming dwarf
galaxies in the infall regions of the Coma cluster and the core of Abell 1367
with respect to the overall supercluster population, indicative of the
infalling dwarf galaxies undergoing a starburst phase. We identify these
starburst galaxies as the precursors of the post-starburst k+A galaxies. We
find that 11.4% of all dwarf (z mag > 15) galaxies in the Coma cluster and 4.8%
in the Abell 1367 have k+A like spectra, while this fraction is just 2.1% when
averaged over the entire supercluster region. We show that in the centre of the
Coma cluster, the (24-z) colour of galaxies is correlated with their optical
(g-r) colour and Halpha emission. By analysing the projected phase space
distribution of galaxies detected at 24micron in Coma, we find that the
(optically) red 24 micron detected galaxies follow the general distribution of
`all' the spectroscopic members, but their (optically) blue counterparts show
interesting features, indicative of recent infall.Comment: 17 pages, 14 figures, accepted for publicaton in MNRA
Evidence of mTOR Activation by an AKT-Independent Mechanism Provides Support for the Combined Treatment of PTEN-Deficient Prostate Tumors with mTOR and AKT Inhibitors
AbstractActivation of the phosphoinositide 3-kinase pathway is commonly observed in human prostate cancer. Loss of function of phosphatase and tensin homolog (PTEN) is associated with the activation of AKT and mammalian target of rapamycin (mTOR) in many cancer cell lines as well as in other model systems. However, activation of mTOR is also dependent of kinases other than AKT. Here, we show that activation of mTOR is not dependent on AKT in a prostate-specific PTEN-deficient mouse model of prostate cancer. Pathway bifurcation of AKT and mTOR was noted in both mouse and human prostate tumors. We demonstrated for the first time that cotargeting mTOR and AKT with ridaforolimus/MK-8669 and M1K-2206, respectively, delivers additive antitumor effects in vivo when compared to single agents. Our preclinical data suggest that the combination of AKT and mTOR inhibitors might be more effective in treating prostate cancer patients than current treatment regimens or either treatment alone
An Interacting Galaxy Pair at the Origin of a Light Echo
In a low-density region of the Shapley supercluster we identified an interacting galaxy pair at redshift z = 0.04865 in which the Seyfert 2 nucleus of the main galaxy (ShaSS 073) is exciting an extended emission line region (EELR, ∼170 kpc^2) in the disk of the less massive companion (ShaSS 622). New integral-field spectroscopy and the multiband data set, spanning from far-ultraviolet to far-infrared and radio wavelengths, allowed us to obtain a detailed description of the ShaSS 622-073 system. The gas kinematics shows hints of interaction, although the overall velocity field shows a quite regular rotation in both galaxies, thus suggesting that we are observing their first encounter as confirmed by the estimated distance of 21 kpc between the two galaxy centers. The detected ∼ 2-3 kpc active galactic nucleus (AGN) outflow and the geometry of the EELR in ShaSS 622 support the presence of a hollow bicone structure. The status and sources of the ionization across the whole system have been analyzed through photoionization models and a Bayesian approach that prove a clear connection between the AGN and the EELR. The luminosity of the AGN (2.4×10^44 erg/s) is a factor of 20 lower than the power needed to excite the gas in the EELR (4.6 ×10^45 erg/s), indicating a dramatic fading of the AGN in the past 3×10^4 yr. ShaSS 073-622 provides all the ingredients listed in the recipe of a light echo where a highly-ionized region maintains memory of a preceding more energetic phase of a now-faded AGN. This is the first case of a light echo observed between two galaxies
BUDHIES - III : the fate of HI and the quenching of galaxies in evolving environments
In a hierarchical Universe clusters grow via the accretion of galaxies from the field, groups and even other clusters. As this happens, galaxies can lose and/or consume their gas reservoirs via different mechanisms, eventually quenching their star formation. We explore the diverse environmental histories of galaxies through a multiwavelength study of the combined effect of ram-pressure stripping and group 'processing' in Abell 963, a massive growing cluster at z = 0.2 from the Blind Ultra Deep HI Environmental Survey (BUDHIES). We incorporate hundreds of new optical redshifts (giving a total of 566 cluster members), as well as Subaru and XMM-Newton data from LoCuSS, to identify substructures and evaluate galaxy morphology, star formation activity, and HI content (via HI deficiencies and stacking) out to 3 x R-200. We find that Abell 963 is being fed by at least seven groups, that contribute to the large number of passive galaxies outside the cluster core. More massive groups have a higher fraction of passive and HI-poor galaxies, while low-mass groups host younger (often interacting) galaxies. For cluster galaxies not associated with groups we corroborate our previous finding that HI gas (if any) is significantly stripped via ram-pressure during their first passage through the intracluster medium, and find mild evidence for a starburst associated with this event. In addition, we find an overabundance of morphologically peculiar and/or star-forming galaxies near the cluster core. We speculate that these arise from the effect of groups passing through the cluster (post-processing). Our study highlights the importance of environmental quenching and the complexity added by evolving environments.Peer reviewe
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