14 research outputs found
Galaxy Orbits for Galaxy Clusters in Sloan Digital Sky Survey and 2dF Galaxy Redshift Survey
We present the results of a study for galaxy orbits in galaxy clusters using
a spectroscopic sample of galaxies in Sloan Digital Sky Survey (SDSS) and 2dF
Galaxy Redshift Survey (2dFGRS). We have determined the member galaxies of
Abell clusters covered by these surveys using the galaxies' redshift and
positional data. We have selected 10 clusters using three criteria: the number
of member galaxies is greater than or equal to 40, the spatial coverage is
complete, and X-ray mass profile is available in the literature. We derive the
radial profile of the galaxy number density and velocity dispersion using all,
early-type, and late-type galaxies for each cluster. We have investigated the
galaxy orbits for our sample clusters with constant and variable velocity
anisotropies over the clustercentric distance using Jeans equation. Using all
member galaxies, the galaxy orbits are found to be isotropic within the
uncertainty for most of sample clusters, although it is difficult to conclude
strongly for some clusters due the large errors and the variation as a function
of the clustercentric distance in the calculated velocity anisotropies. We
investigated the orbital difference between early-type and late-type galaxies
for four sample clusters, and found no significant difference between them.Comment: 59 pages, 21 figures. To appear in ApJ. Paper with high resolution
figures are available at http://astro.kias.re.kr/~hshwang/papers/orbit.pd
Substructure lensing in galaxy clusters as a constraint on low-mass sterile neutrinos in tensor-vector-scalar theory: The straight arc of Abell 2390
Certain covariant theories of the modified Newtonian dynamics paradigm seem
to require an additional hot dark matter (HDM) component - in the form of
either heavy ordinary neutrinos or more recently light sterile neutrinos (SNs)
with a mass around 11eV - to be relieved of problems ranging from cosmological
scales down to intermediate ones relevant for galaxy clusters. Here we suggest
using gravitational lensing by galaxy clusters to test such a marriage of
neutrino HDM and modified gravity, adopting the framework of
tensor-vector-scalar theory (TeVeS). Unlike conventional cold dark matter
(CDM), such HDM is subject to strong phase-space constraints, which allows one
to check cluster lens models inferred within the modified framework for
consistency. Since the considered HDM particles cannot collapse into
arbitrarily dense clumps and only form structures well above the galactic
scale, systems which indicate the need for dark substructure are of particular
interest. As a first example, we study the cluster lens Abell 2390 and its
impressive straight arc with the help of numerical simulations. Based on our
results, we outline a general and systematic approach to model cluster lenses
in TeVeS which significantly reduces the calculation complexity. We further
consider a simple bimodal lens configuration, capable of producing the straight
arc, to demonstrate our approach. We find that such a model is marginally
consistent with the hypothesis of 11eV SNs. Future work including more detailed
and realistic lens models may further constrain the necessary SN distribution
and help to conclusively assess this point. Cluster lenses could therefore
provide an interesting discriminator between CDM and such modified gravity
scenarios supplemented by SNs or other choices of HDM.Comment: 22 pages, 14 figures, 2 tables; minor changes to match accepted
versio
The Merger in Abell 576: A Line‐of‐Sight Bullet Cluster?
Using a combination of Chandra and XMM observations, we confirmed the
presence of a significant velocity gradient along the NE/E-W/SW direction in
the intracluster gas of the cluster Abell 576. The results are consistent with
a previous ASCA SIS analysis of this cluster. The error weighted average over
ACIS-S3, EPIC MOS 1 & 2 spectrometers for the maximum velocity difference is
>3.3E03 km/s at the 90% confidence level, similar to the velocity limits
estimated indirectly for the "bullet" cluster (1E0657-56). The probability that
the velocity gradient is generated by standard random gain fluctuations with
Chandra and XMM is <0.1%. The regions of maximum velocity gradient are in CCD
zones that have the lowest temporal gain variations. It is unlikely that the
velocity gradient is due to Hubble distance differences between projected
clusters (probability<~0.01%). We mapped the distribution of elemental
abundance ratios across the cluster and detected a strong chemical
discontinuity using the abundance ratio of silicon to iron, equivalent to a
variation from 100% SN Ia iron mass fraction in the West-Northwest regions to
32% in the Eastern region. The "center" of the cluster is located at the
chemical discontinuity boundary, which is inconsistent with the radially
symmetric chemical gradient found in some regular clusters, but consistent with
a cluster merging scenario. We predict that the velocity gradient as measured
will produce a variation of the CMB temperature towards the East of the core of
the cluster that will be detectable by current and near-future bolometers. The
measured velocity gradient opens for the possibility that this cluster is
passing through a near line-of-sight merger stage where the cores have recently
crossed.Comment: 24 pages, 2 tables and 20 figures; accepted for publication in the
Astrophysical Journal. For full version with all figures click on
http://www.astro.lsa.umich.edu/~rdupke/a576_web.pd