902 research outputs found
An XMM-Newton study of the sub-structure in M87's halo
The high signal to noise and good point spread function of XMM have allowed
the first detailed study of the interaction between the thermal and radio
emitting plasma in the central regions of M87. We show that the X-ray emitting
structure, previously seen by ROSAT, is thermal in nature and that the east and
southwest extensions in M87's X-ray halo have a significantly lower temperature
(kT= 1.5 keV) than the surrounding ambient medium (kT= 2.3 keV). There is
little or no evidence for non-thermal emission with an upper limit on the
contribution of a power law component of spectral index flatter than 3 being
less than 1% of the flux in the region of the radio lobes.Comment: 6 pages, 8 color figures, to be published in A&A, number 36
Violent Relaxation of Indistinguishable Objects and Neutrino Hot Dark Matter in Clusters of Galaxies
The statistical mechanical investigation of violent relaxation (Lynden-Bell
1967) is extended to indistinguishable objects. It is found that,
coincidentally, the equilibrium distribution is the same as that obtained for
classical objects. For massive neutrinos, the Tremaine \& Gunn (1979) phase
space bound is revisited and reinterpretated as the limit indicating the onset
of degeneracy related to the coarse-grained phase space distribution. In the
context of one of the currently most popular cosmological models, the Cold and
Hot Dark Matter (CHDM) model (Primack et al. 1995), the onset of degeneracy may
be of importance in the core region of clusters of galaxies. Degeneracy allows
the neutrino HDM density to exceed the limit imposed by the Tremaine \& Gunn
(1979) bound while accounting for the phase space bound.Comment: AASTeX, 16 pages, 2 EPS figures, uses aas2pp4.sty. Accepted by ApJ
Letter
Metal transport by gas sloshing in M87
We present the results of an XMM-Newton mosaic covering the central ~200 kpc
of the nearby Virgo cluster. We focus on a strong surface brightness
discontinuity in the outskirts of the brightest cluster galaxy, M87. Using both
XMM-Newton and Suzaku, we derive accurate temperature and metallicity profiles
across this feature and show that it is a cold front probably due to sloshing
of the Virgo ICM. It is also associated with a discontinuity in the chemical
composition. The gas in the inner, bright region of the front is ~40% more
abundant in Fe than the gas outside the front, suggesting the important role of
sloshing in transporting metals through the ICM. For the first time, we provide
a quantitative estimate of the mass of Fe transported by a cold front. This
amounts to ~6% of the total Fe mass within the radial range affected by
sloshing, significantly more than the amount of metals transported by the AGN
in the same cluster core. The very low Fe abundance of only ~0.2 solar
immediately outside the cold front at a radius of 90 kpc suggests we are
witnessing first-hand the transport of higher metallicity gas into a pristine
region, whose abundance is typical of the cluster outskirts. The Mg/Fe and O/Fe
abundance ratios remain approximately constant over the entire radial range
between the centre of M87 and the faint side of the cold front, which requires
the presence of a centrally peaked distribution not only for Fe but also for
core-collapse type supernova products. This peak may stem from the star
formation triggered as the BCG assembled during the protocluster phase.Comment: accepted for publication in MNRA
XMM-Newton detection of two clusters of galaxies with strong SPT Sunyaev-Zel'dovich effect signatures
We report on the discovery of two galaxy clusters, SPT-CL J2332-5358 and
SPT-CL J2342-5411, in X-rays. These clusters were also independently detected
through their Sunyaev-Zel'dovich effect by the South Pole Telescope, and
confirmed in the optical band by the Blanco Cosmology Survey. They are thus the
first clusters detected under survey conditions by all major cluster search
approaches. The X-ray detection is made within the frame of the XMM-BCS cluster
survey utilizing a novel XMM-Newton mosaic mode of observations. The present
study makes the first scientific use of this operation mode. We estimate the
X-ray spectroscopic temperature of SPT-CL J2332-5358 (at redshift z=0.32) to T
= 9.3 (+3.3/-1.9) keV, implying a high mass, M_{500} = 8.8 +/- 3.8 \times
10^{14} M_{sun}. For SPT-CL J2342-5411, at z=1.08, the available X-ray data
doesn't allow us to directly estimate the temperature with good confidence.
However, using our measured luminosity and scaling relations we estimate that T
= 4.5 +/- 1.3 keV and M_{500} = 1.9 +/- 0.8 \times 10^{14} M_{sun}. We find a
good agreement between the X-ray masses and those estimated from the
Sunyaev-Zel'dovich effect.Comment: Submitted to A&A, 8 pages, 5 figures, 1 tabl
ROSAT-SDSS Galaxy Clusters Survey. I. The Catalog and the correlation of X-ray and optical properties
For a detailed comparison of the appearance of cluster of galaxies in X-rays
and in the optical, we have compiled a comprehensive database of X-ray and
optical properties of a sample of clusters based on the largest available X-ray
and optical surveys: the ROSAT All Sky Survey (RASS) and the Sloan Digital Sky
Survey (SDSS). The X-ray galaxy clusters of this RASS-SDSS catalog cover a wide
range of masses, from groups of 10^{12.5} solar masses to massive clusters of
10^{15} solar masses in the redshift range from 0.002 to 0.45. The RASS-SDSS
sample comprises all the X-ray selected objects already observed by the Sloan
Digital Sky Survey (114 clusters). For each system we have uniformly determined
the X-ray and optical properties. The total optical luminosity can be
determined with a typical uncertainty of 20% with a result independent of the
choice of local or global background subtraction. We found that the z band
cluster luminosity determined within an aperture of 0.5 Mpc h_{70}^(-1)
provides the best correlation with the X-ray luminosity with a scatter of about
60-70%. The scatter decreases to less than 40% if the correlation is limited to
the bright X-ray clusters. The resulting correlation of L_X and L_{op} in the z
and i bands shows a logarithmic slope of 0.38, a value not consistent with the
assumption of a constant M/L. Consistency is found, however, for an increasing
M/L with luminosity as suggested by other observations. We also investigated
the correlation between L_{op} and the X-ray temperature obtaining the same
result.Comment: Accepted for publication in A&A, 47 pages, 19 figure
Computing tolerance parameters for fixturing and feeding
Fixtures and feeders are important components of automated assembly
systems: fixtures accurately hold parts and feeders move parts into alignment.
These components can fail when part shape varies. Parametric tolerance
classes specify how much variation is allowable. In this paper we consider
fixturing convex polygonal parts using right-angle brackets and feeding
polygonal parts on conveyor belts using sequences of vertical fences. For
both cases, we define new tolerance classes and give algorithms for computing
the parameter specifications such that the fixture or feeder will work for
all parts in the tolerance class. For fixturing we give an O(1) algorithm to
compute the dimensions of rectangular tolerance zones. For feeding we give
an O(n2) algorithm to compute the radius of the largest allowable tolerance
zone around each vertex. For each, we give an O(n) time algorithm for testing
if an n-sided part is in the tolerance class
- …