5,766 research outputs found
The Entire Virial Radius of the Fossil Cluster RXJ1159+5531: I. Gas Properties
Previous analysis of the fossil-group/cluster RXJ1159+5531 with X-ray
observations from a central Chandra pointing and an offset-North Suzaku
pointing indicate a radial intracluster medium (ICM) entropy profile at the
virial radius () consistent with predictions from gravity-only
cosmological simulations, in contrast to other cool-core clusters. To examine
the generality of these results, we present three new Suzaku observations that,
in conjunction with the North pointing, provide complete azimuthal coverage out
to . With two new Chandra ACIS-I observations overlapping the
North Suzaku pointing, we have resolved 50\% of the cosmic X-ray
background there. We present radial profiles of the ICM density, temperature,
entropy, and pressure obtained for each of the four directions. We measure only
modest azimuthal scatter in the ICM properties at between the
Suzaku pointings: 7.6\% in temperature and 8.6\% in density, while the
systematic errors can be significant. The temperature scatter, in particular,
is lower than that studied at for a small number of other
clusters observed with Suzaku. These azimuthal measurements verify that
RXJ1159+5531 is a regular, highly relaxed system. The well-behaved entropy
profiles we have measured for RXJ1159+5531 disfavor the weakening of the
accretion shock as an explanation of the entropy flattening found in other
cool-core clusters but is consistent with other explanations such as gas
clumping, electron-ion non-equilibrium, non-thermal pressure support, and
cosmic ray acceleration. Finally, we mention that the large-scale galaxy
density distribution of RXJ1159+5531 seems to have little impact on its gas
properties near .Comment: Accepted for publication in Ap
Nonrepetitive Colourings of Planar Graphs with Colours
A vertex colouring of a graph is \emph{nonrepetitive} if there is no path for
which the first half of the path is assigned the same sequence of colours as
the second half. The \emph{nonrepetitive chromatic number} of a graph is
the minimum integer such that has a nonrepetitive -colouring.
Whether planar graphs have bounded nonrepetitive chromatic number is one of the
most important open problems in the field. Despite this, the best known upper
bound is for -vertex planar graphs. We prove a
upper bound
CM relations in fibered powers of elliptic families
Let be the Legendre family of elliptic curves. Given linearly
independent points we prove that there are
at most finitely many complex numbers such that
has complex multiplication and are
dependent over . This implies a positive answer to a
question of Bertrand and, combined with a previous work in collaboration with
Capuano, proves the Zilber-Pink conjecture for a curve in a fibered power of an
elliptic scheme when everything is defined over .Comment: The formulation of Theorem 2.1 is now correc
Hydrostatic Gas Constraints On Supermassive Black Hole Masses: Implications For Hydrostatic Equilibrium And Dynamical Modeling In A Sample Of Early-Type Galaxies
We present new mass measurements for the supermassive black holes (SMBHs) in the centers of three early-type galaxies. The gas pressure in the surrounding, hot interstellar medium (ISM) is measured through spatially resolved spectroscopy with the Chandra X-ray Observatory, allowing the SMBH mass (M(BH)) to be inferred directly under the hydrostatic approximation. This technique does not require calibration against other SMBH measurement methods and its accuracy depends only on the ISM being close to hydrostatic, which is supported by the smooth X-ray isophotes of the galaxies. Combined with results from our recent study of the elliptical galaxy NGC4649, this brings the number of galaxies with SMBHs measured in this way to four. Of these, three already have mass determinations from the kinematics of either the stars or a central gas disk, and hence join only a handful of galaxies with MBH measured by more than one technique. We find good agreement between the different methods, providing support for the assumptions implicit in both the hydrostatic and the dynamical models. The stellar mass-to-light ratios for each galaxy inferred by our technique are in agreement with the predictions of stellar population synthesis models assuming a Kroupa initial mass function (IMF). This concurrence implies that no more than similar to 10%-20% of the ISM pressure is nonthermal, unless there is a conspiracy between the shape of the IMF and nonthermal pressure. Finally, we compute Bondi accretion rates (M(bondi)), finding that the two galaxies with the highest M(bondi) exhibit little evidence of X-ray cavities, suggesting that the correlation with the active galactic nuclei jet power takes time to be established.NASA NAS5-26555, NNG04GE76G, G07-8083XAstronom
AGN Feedback in Galaxy Groups: the two interesting cases of AWM 4 and NGC 5044
We present AGN feedback in the interesting cases of two groups: AWM 4 and NGC
5044. AWM 4 is characterized by a combination of properties which seems to defy
the paradigm for AGN heating in cluster cores: a flat inner temperature profile
indicative of a past, major heating episode which completely erased the cool
core, as testified by the high central cooling time (> 3 Gyrs) and by the high
central entropy level (~ 50 keV cm^2), and yet an active central radio galaxy
with extended radio lobes out to 100 kpc, revealing recent feeding of the
central massive black hole. A recent Chandra observation has revealed the
presence of a compact cool corona associated with the BCG, solving the puzzle
of the apparent lack of low entropy gas surrounding a bright radio source, but
opening the question of its origin. NGC 5044 shows in the inner 10 kpc a pair
of cavities together with a set of bright filaments. The cavities are
consistent with a recent AGN outburst as also indicated by the extent of dust
and H_alpha emission even though the absence of extended 1.4 GHz emission
remains to be explained. The soft X-ray filaments coincident with H_alpha and
dust emission are cooler than those which do not correlate with optical and
infrared emission, suggesting that dust-aided cooling can contribute to the
overall cooling. For the first time sloshing cold fronts at the scale of a
galaxy group have been observed in this object.Comment: 4 pages, 1 figure, to appear in proceedings of the conference "The
Monster's Fiery Breath: Feedback in Galaxies, Groups, and Clusters", June
2009, Madison Wisconsi
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