146 research outputs found
The late merging phase of a galaxy cluster : XMM EPIC Observations of A3266
We present a mosaic of five XMM-Newton observations of the nearby
() merging galaxy cluster Abell 3266. We use the spectro-imaging
capabilities of \xmm to build precise (projected) temperature, entropy,
pressure and Fe abundance maps. The temperature map exhibits a curved,
large-scale hot region, associated with elevated entropy levels, very similar
to that foreseen in numerical simulations. The pressure distribution is
disturbed in the central region but is remarkably regular on large scales. The
Fe abundance map indicates that metals are inhomogeneously distributed across
the cluster. Using simple physical calculations and comparison with numerical
simulations, we discuss in detail merging scenarios that can reconcile the
observed gas density, temperature and entropy structure, and the galaxy density
distribution
Optical and ROSAT X-ray observations of the dwarf nova OY Carinae in superoutburst and quiescence
We present ROSAT X-ray and optical light curves of the 1994 February
superoutburst of the eclipsing SU UMa dwarf nova OY Carinae. There is no
eclipse of the flux in the ROSAT HRI light curve. Contemporaneous `wide B' band
optical light curves show extensive superhump activity and dips at superhump
maximum. Eclipse mapping of these optical light curves reveals a disc with a
considerable physical flare, even three days into the superoutburst decline.
We include a later (1994 July) ROSAT PSPC observation of OY Car that allows
us to put constraints on the quiescent X-ray spectrum. We find that while there
is little to choose between OY Car and its fellow high inclination systems with
regard to the temperature of the emitting gas and the emission measure, we have
difficulties reconciling the column density found from our X-ray observation
with the column found in HST UV observations by Horne et al. (1994). The
obvious option is to invoke time variability.Comment: 16 pages, 14 figures, accepted for publication in MNRA
The stellar mass function of galaxies in Planck-selected clusters at 0.5 < z < 0.7: new constraints on the timescale and location of satellite quenching
We study the abundance of star-forming and quiescent galaxies in a sample of
21 massive clusters at 0.5<z<0.7, detected with the Planck satellite. We
measure the cluster galaxy stellar mass function (SMF), which is a fundamental
observable to study and constrain the formation and evolution of galaxies. Our
measurements are based on homogeneous and deep multi-band photometry spanning
u- to the Ks-band for each cluster and are supported by spectroscopic data from
different programs. The galaxy population is separated between quiescent and
star-forming galaxies based on their rest-frame U-V and V-J colours. The SMF is
compared to that of field galaxies at the same redshifts, using data from the
COSMOS/UltraVISTA survey. We find that the shape of the SMF of star-forming
galaxies does not depend on environment, while the SMF of quiescent galaxies
has a significantly steeper low-mass slope in the clusters compared to the
field. We estimate the environmental quenching efficiency (f_EQ), i.e. the
probability for a galaxy that would normally be star forming in the field, to
be quenched due to its environment. The f_EQ shows no stellar-mass dependence
in any environment, but it increases from 40% in the cluster outskirts to ~90%
in the cluster centres. The radial signature of f_EQ provides constraints on
where the dominant quenching mechanism operates in these clusters and on what
timescale. Exploring these using a simple model based on galaxy orbits obtained
from an N-body simulation, we find a clear degeneracy between both parameters.
For example, the quenching process may either be triggered on a long (~3 Gyr)
time scale at large radii (r~8R_500), or happen well within 1 Gyr at r<R_500.
The radius where quenching is triggered is at least r_quench> 0.67R_500
(95%CL). The ICM density at this location suggests that ram-pressure stripping
of the cold gas is a likely cause of quenching. [Abridged]Comment: 16 pages, 12 figures, accepted for publication in A&
Are fossil groups a challenge of the Cold Dark Matter paradigm?
We study six groups and clusters of galaxies suggested in the literature to
be `fossil' systems (i.e. to have luminous diffuse X-ray emission and a
magnitude gap of at least 2 mag-R between the first and the second ranked
member within half of the virial radius), each having good quality X-ray data
and SDSS spectroscopic or photometric coverage out to the virial radius. The
poor cluster AWM4 is clearly established as a fossil system, and we confirm the
fossil nature of four other systems (RXJ1331.5+1108, RXJ1340.6+4018,
RXJ1256.0+2556 and RXJ1416.4+2315), while the cluster RXJ1552.2+2013 is
disqualified as fossil system. For all systems we present the luminosity
functions within 0.5 and 1 virial radius that are consistent, within the
uncertainties, with the universal luminosity function of clusters. For the five
bona fide fossil systems, having a mass range 2x10^13-3x10^14 M_Sun, we compute
accurate cumulative substructure distribution functions (CSDFs) and compare
them with the CSDFs of observed and simulated groups/clusters available in the
literature. We demonstrate that the CSDFs of fossil systems are consistent with
those of normal observed clusters and do not lack any substructure with respect
to simulated galaxy systems in the cosmological LambdaCDM framework. In
particular, this holds for the archetype fossil group RXJ1340.6+4018 as well,
contrary to earlier claims.Comment: Accepted for publication on MNRAS. Minor changes in sections 2.1 and
6. 13 pages, 4 eps figure
The X-ray luminous galaxy cluster XMMU J1007.4+1237 at z=1.56 - The dawn of starburst activity in cluster cores
Observational galaxy cluster studies at z>1.5 probe the formation of the
first massive M>10^14 Msun dark matter halos, the early thermal history of the
hot ICM, and the emergence of the red-sequence population of quenched
early-type galaxies. We present first results for the newly discovered X-ray
luminous galaxy cluster XMMU J1007.4+1237 at z=1.555, detected and confirmed by
the XMM-Newton Distant Cluster Project (XDCP) survey. We selected the system as
a serendipitous weak extended X-ray source in XMM-Newton archival data and
followed it up with two-band near-infrared imaging and deep optical
spectroscopy. We can establish XMMU J1007.4+1237 as a spectroscopically
confirmed, massive, bona fide galaxy cluster with a bolometric X-ray luminosity
of Lx=(2.1+-0.4)\times 10^44 erg/s, a red galaxy population centered on the
X-ray emission, and a central radio-loud brightest cluster galaxy. However, we
see evidence for the first time that the massive end of the galaxy population
and the cluster red-sequence are not yet fully in place. In particular, we find
ongoing starburst activity for the third ranked galaxy close to the center and
another slightly fainter object. At a lookback time of 9.4Gyr, the cluster
galaxy population appears to be caught in an important evolutionary phase,
prior to full star-formation quenching and mass assembly in the core region.
X-ray selection techniques are an efficient means of identifying and probing
the most distant clusters without any prior assumptions about their galaxy
content.Comment: 6 pages, 3 color figures, accepted for publication in A&
Robust transcriptome-wide discovery of RNA-binding protein binding sites with enhanced CLIP (eCLIP)
As RNA-binding proteins (RBPs) play essential roles in cellular physiology by interacting with target RNA molecules, binding site identification by UV crosslinking and immunoprecipitation (CLIP) of ribonucleoprotein complexes is critical to understanding RBP function. However, current CLIP protocols are technically demanding and yield low-complexity libraries with high experimental failure rates. We have developed an enhanced CLIP (eCLIP) protocol that decreases requisite amplification by ~1,000-fold, decreasing discarded PCR duplicate reads by ~60% while maintaining single-nucleotide binding resolution. By simplifying the generation of paired IgG and size-matched input controls, eCLIP improves specificity in the discovery of authentic binding sites. We generated 102 eCLIP experiments for 73 diverse RBPs in HepG2 and K562 cells (available at https://www.encodeproject.org), demonstrating that eCLIP enables large-scale and robust profiling, with amplification and sample requirements similar to those of ChIP-seq. eCLIP enables integrative analysis of diverse RBPs to reveal factor-specific profiles, common artifacts for CLIP and RNA-centric perspectives on RBP activity
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