1,602 research outputs found
The Formation of Low-Mass Cluster Galaxies and the Universal Initial Galaxy Mass Function
Clusters of galaxies have an observed over-density of low-luminosity systems
in comparison to the field, although it is not yet agreed whether this effect
is the result of initial galaxy mass functions that vary with environment or
galaxy evolutionary effects. In this letter we argue that this over-density is
the result of low-mass systems with red colors that are over-populating the
faint-end of the observed luminosity function in the nearby rich cluster Abell
0426. We show that the luminosity function of Abell 0426 becomes steeper, from
the field value alpha = -1.25+/-0.05 to alpha=-1.44+/-0.04, due to a recently
identified population of red low-mass cluster galaxies that are possibly the
remnants of dynamical stripped high-mass systems. We further demonstrate,
through simple models of stripping effects, how cluster luminosity functions
can become artificially steep over time from the production of these low-mass
cluster galaxies.Comment: Accepted to ApJ letter
Critical and Near-Critical Branching Processes
Scale-free dynamics in physical and biological systems can arise from a
variety of causes. Here, we explore a branching process which leads to such
dynamics. We find conditions for the appearance of power laws and study
quantitatively what happens to these power laws when such conditions are
violated. From a branching process model, we predict the behavior of two
systems which seem to exhibit near scale-free behavior--rank-frequency
distributions of number of subtaxa in biology, and abundance distributions of
genotypes in an artificial life system. In the light of these, we discuss
distributions of avalanche sizes in the Bak-Tang-Wiesenfeld sandpile model.Comment: 9 pages LaTex with 10 PS figures. v.1 of this paper contains results
from non-critical sandpile simulations that were excised from the published
versio
Paravasation with cyclophosphamide - Case report of tissue necrosis in a patient with primary breast cancer
Background: Paravasation is a rare but severe complication of treatment with cytotoxic agents. Some anticancer drugs are considered to be of high toxicity (vesicant), some are merely irritant, and some are regarded as nearly non-toxic to healthy tissue as is the case with cyclophosphamide. Case Report: In this report, we present the first case of severe tissue damage caused by a paravasation of cyclophosphamide in a breast cancer patient receiving chemotherapy. Conclusion: Therefore, every attending oncological physician should be aware of the possibility of severe tissue damage as a consequence of cyclophosphamide paravasation
An extension of the SHARC survey
We report on our search for distant clusters of galaxies based on optical and
X-ray follow up observations of X-ray candidates from the SHARC survey. Based
on the assumption that the absence of bright optical or radio counterparts to
possibly extended X-ray sources could be distant clusters. We have obtained
deep optical images and redshifts for several of these objects and analyzed
archive XMM-Newton or Chandra data where applicable. In our list of candidate
clusters, two are probably galaxy structures at redshifts of z0.51 and
0.28. Seven other structures are possibly galaxy clusters between z0.3
and 1. Three sources are identified with QSOs and are thus likely to be X-ray
point sources, and six more also probably fall in this category. One X-ray
source is spurious or variable. For 17 other sources, the data are too sparse
at this time to put forward any hypothesis on their nature. We also
serendipitously detected a cluster at z=0.53 and another galaxy concentration
which is probably a structure with a redshift in the [0.15-0.6] range. We
discuss these results within the context of future space missions to
demonstrate the necessity of a wide field of view telescope optimized for the
0.5-2 keV range.Comment: Accepted in A&
Density profiles and substructure of dark matter halos: converging results at ultra-high numerical resolution
Can N-body simulations reliably determine the structural properties of dark
matter halos? Focussing on a Virgo-sized galaxy cluster, we increase the
resolution of current ``high resolution simulations'' by almost an order of
magnitude to examine the convergence of the important physical quantities. We
have 4 million particles within the cluster and force resolution 0.5 kpc/h
(0.05% of the virial radius). The central density profile has a logarithmic
slope of -1.5, as found in lower resolution studies of the same halo,
indicating that the profile has converged to the ``physical'' limit down to
scales of a few kpc. Also the abundance of substructure is consistent with that
derived from lower resolution runs; on the scales explored, the mass and
circular velocity functions are close to power laws of exponents ~ -1.9 and -4.
Overmerging appears to be globally unimportant for suhalos with circular
velocities > 100 km/s. We can trace most of the cluster progenitors from z=3 to
the present; the central object (the dark matter analog of a cD galaxy)is
assembled between z=3 and 1 from the merging of a dozen halos with v_circ \sim
300 km/s. The mean circular velocity of the subhalos decreases by ~ 20% over 5
billion years, due to tidal mass loss. The velocity dispersions of halos and
dark matter globally agree within 10%, but the halos are spatially anti-biased,
and, in the very central region of the cluster, they show positive velocity
bias; however, this effect appears to depend on numerical resolution.Comment: 19 pages, 13 figures, ApJ, in press. Text significantly clarifie
A family of diameter-based eigenvalue bounds for quantum graphs
We establish a sharp lower bound on the first non-trivial eigenvalue of the
Laplacian on a metric graph equipped with natural (i.e., continuity and
Kirchhoff) vertex conditions in terms of the diameter and the total length of
the graph. This extends a result of, and resolves an open problem from, [J. B.
Kennedy, P. Kurasov, G. Malenov\'a and D. Mugnolo, Ann. Henri Poincar\'e 17
(2016), 2439--2473, Section 7.2], and also complements an analogous lower bound
for the corresponding eigenvalue of the combinatorial Laplacian on a discrete
graph. We also give a family of corresponding lower bounds for the higher
eigenvalues under the assumption that the total length of the graph is
sufficiently large compared with its diameter. These inequalities are sharp in
the case of trees.Comment: Substantial revision of v1. The main result, originally for the first
eigenvalue, has been generalised to the higher ones. The title has been
changed and the proofs substantially reorganised to reflect the new result,
and a section containing concluding remarks has been adde
On the Asymptotic Dynamics of a Quantum System Composed by Heavy and Light Particles
We consider a non relativistic quantum system consisting of heavy and
light particles in dimension three, where each heavy particle interacts with
the light ones via a two-body potential . No interaction is assumed
among particles of the same kind. Choosing an initial state in a product form
and assuming sufficiently small we characterize the asymptotic
dynamics of the system in the limit of small mass ratio, with an explicit
control of the error. In the case K=1 the result is extended to arbitrary
. The proof relies on a perturbative analysis and exploits a
generalized version of the standard dispersive estimates for the
Schr\"{o}dinger group. Exploiting the asymptotic formula, it is also outlined
an application to the problem of the decoherence effect produced on a heavy
particle by the interaction with the light ones.Comment: 38 page
Environmental Dependence of the Fundamental Plane of Galaxy Clusters
Galaxy clusters approximate a planar (FP) distribution in a three-dimensional
parameter space which can be characterized by optical luminosity, half-light
radius, and X-ray luminosity. Using a high-quality catalog of cluster
redshifts, we find the nearest neighbor cluster for those common to an FP study
and the cluster catalog. Examining scatter about the FP, we find 99.2%
confidence that it is dependent on nearest neighbor distance. Our study of
X-Ray clusters finds that those with high central gas densities are
systematically closer to neighbor clusters. If we combine results here with
those of Fritsch and Buchert, we find an explanation for some of our previous
conclusions: Clusters in close proximity to other clusters are more likely to
have massive cooling flows because they are more relaxed and have higher
central gas densities.Comment: Accepted for publication in Astrophysical Journal Letters. Moderate
revisions, including more statistical analysis and discussion. Latex, 7 page
The XMM-LSS survey: the Class 1 cluster sample over the extended 11 deg and its spatial distribution
This paper presents 52 X-ray bright galaxy clusters selected within the 11
deg XMM-LSS survey. 51 of them have spectroscopic redshifts
(), one is identified at , and all together make
the high-purity "Class 1" (C1) cluster sample of the XMM-LSS, the highest
density sample of X-ray selected clusters with a monitored selection function.
Their X-ray fluxes, averaged gas temperatures (median keV),
luminosities (median ergs/s) and total mass
estimates (median ) are measured, adapting to
the specific signal-to-noise regime of XMM-LSS observations. The redshift
distribution of clusters shows a deficit of sources when compared to the
cosmological expectations, regardless of whether WMAP-9 or Planck-2013 CMB
parameters are assumed. This lack of sources is particularly noticeable at . However, after quantifying uncertainties due to small
number statistics and sample variance we are not able to put firm (i.e. ) constraints on the presence of a large void in the cluster
distribution. We work out alternative hypotheses and demonstrate that a
negative redshift evolution in the normalization of the relation
(with respect to a self-similar evolution) is a plausible explanation for the
observed deficit. We confirm this evolutionary trend by directly studying how
C1 clusters populate the space, properly accounting for selection
biases. We point out that a systematically evolving, unresolved, central
component in clusters and groups (AGN contamination or cool core) can impact
the classification as extended sources and be partly responsible for the
observed redshift distribution.[abridged]Comment: 33 pages, 21 figures, 3 tables ; accepted for publication in MNRA
The descendents of Lyman Break Galaxies in galaxy clusters: spatial distribution and orbital properties
We combine semi-analytical methods with a ultra-high resolution simulation of
a galaxy cluster (of mass 2.3 10^14h-1Msolar, and 4 10^6 particles within its
virial radius) formed in a standard CDM universe to study the spatial
distribution and orbital properties of the present-day descendents of Lyman
Break Galaxies (LBGs). At the present time only five (out of 12) of halos
containing LBGs survive as separate entities inside the cluster virial radius.
Their circular velocities are in the range 200 - 550 km/sec. Seven halos merged
together to form the central object at the very center of the cluster. Using
semi-analytical modeling of galaxy evolution we show that descendents of halos
containing LBGs now host giant elliptical galaxies. Galaxy orbits are radial,
with a pericenter to apocenter ratio of about 1:5. The orbital eccentricities
of LBGs descendents are statistically indistinguishable from those of the
average galaxy population inside the cluster, suggesting that the orbits of
these galaxies are not significantly affected by dynamical friction decay after
the formation of the cluster's main body. In this cluster, possibly due to its
early formation time, the descendents of LBGs are contained within the central
60% of the cluster virial radius and have an orbital velocity dispersion lower
than the global galaxy population, originating a mild luminosity segregation
for the brightest cluster members. Mass estimates based only on LBGs
descendents (especially including the central cD) reflect this bias in space
and velocity and underestimate the total mass of this well virialized cluster
by up to a factor of two compared to estimates using at least 20 cluster
members.Comment: 6 Pages, 2 Postscript figures. Submitted to Ap
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