770 research outputs found
X-ray exploration of the outskirts of the nearby Centaurus cluster using Suzaku and Chandra
We present Suzaku observations of the Centaurus cluster out to 0.95r200,
taken along a strip to the north west. We have also used congruent Chandra
observations of the outskirts to resolve point sources down to a threshold flux
around 7 times lower than that achievable with just Suzaku data, considerably
reducing the systematic uncertainties in the cosmic X-ray background emission
in the outskirts. We find that the temperature decreases by a factor of 2 from
the peak temperature to the outskirts. The entropy profile demonstrates a
central excess (within 0.5r200) over the baseline entropy profile predicted by
simulations of purely gravitational hierarchical structure formation. In the
outskirts the entropy profile is in reasonable agreement with the baseline
entropy profile from Voit et al., but lies slightly below it. We find that the
pressure profile agrees with the universal pressure profile of Arnaud et al.
but lies slightly above it in the outskirts. The excess pressure and decrement
in entropy in the outskirts appear to be the result of an excess in the
measured gas density, possible due to gas clumping biasing the density
measurements high. The gas mass fraction rises and reaches the mean cosmic
baryon fraction at the largest radius studied. The clumping corrected gas mass
fraction agrees with the expected hot gas fraction and with the simulations of
Young et al. We further the analysis of Walker et al. which studied the shapes
of the entropy profiles of the clusters so far explored in the outskirts with
Suzaku. When scaled by the self similar entropy the Suzaku entropy profiles
demonstrate a central excess over the baseline entropy profile, and are
consistent with it at around r500 . However outside r500 the entropy profiles
tend to lie below the baseline entropy profile.Comment: 17 pages, 15 figures. Accepted for publication in MNRA
Serendipitous discovery of an extended X-ray jet without a radio counterpart in a high-redshift quasar
A recent Chandra observation of the nearby galaxy cluster Abell 585 has led
to the discovery of an extended X-ray jet associated with the high-redshift
background quasar B3 0727+409, a luminous radio source at redshift z=2.5. This
is one of only few examples of high-redshift X-ray jets known to date. It has a
clear extension of about 12", corresponding to a projected length of ~100 kpc,
with a possible hot spot located 35" from the quasar. The archival high
resolution VLA maps surprisingly reveal no extended jet emission, except for
one knot about 1.4" from the quasar. The high X-ray to radio luminosity ratio
for this source appears consistent with the amplification
expected from the inverse Compton radiative model. This serendipitous discovery
may signal the existence of an entire population of similar systems with bright
X-ray and faint radio jets at high redshift, a selection bias which must be
accounted for when drawing any conclusions about the redshift evolution of jet
properties and indeed about the cosmological evolution of supermassive black
holes and active galactic nuclei in general
Feedback under the microscope: thermodynamic structure and AGN driven shocks in M87
(abridged) Using a deep Chandra exposure (574 ks), we present high-resolution
thermodynamic maps created from the spectra of 16,000 independent
regions, each with 1,000 net counts. The excellent spatial resolution of
the thermodynamic maps reveals the dramatic and complex temperature, pressure,
entropy and metallicity structure of the system. Excluding the 'X-ray arms',
the diffuse cluster gas at a given radius is strikingly isothermal. This
suggests either that the ambient cluster gas, beyond the arms, remains
relatively undisturbed by AGN uplift, or that conduction in the intracluster
medium (ICM) is efficient along azimuthal directions. We confirm the presence
of a thick (40 arcsec or 3 kpc) ring of high pressure gas at a
radius of 180 arcsec (14 kpc) from the central AGN. We verify that
this feature is associated with a classical shock front, with an average Mach
number M = 1.25. Another, younger shock-like feature is observed at a radius of
40 arcsec (3 kpc) surrounding the central AGN, with an estimated
Mach number M > 1.2. As shown previously, if repeated shocks occur every
10 Myrs, as suggested by these observations, then AGN driven weak shocks
could produce enough energy to offset radiative cooling of the ICM. A high
significance enhancement of Fe abundance is observed at radii 350 - 400 arcsec
(27 - 31 kpc). This ridge is likely formed in the wake of the rising bubbles
filled with radio-emitting plasma that drag cool, metal-rich gas out of the
central galaxy. We estimate that at least solar masses of
Fe has been lifted and deposited at a radius of 350-400 arcsec; approximately
the same mass of Fe is measured in the X-ray bright arms, suggesting that a
single generation of buoyant radio bubbles may be responsible for the observed
Fe excess at 350 - 400 arcsec.Comment: 18 pages, 16 figures. Accepted to MNRA
The X-ray coronae of the two brightest galaxies in the Coma cluster
We use deep Chandra X-ray Observatory observations to examine the coronae of
the two brightest cluster galaxies in the Coma cluster of galaxies, NGC 4874
and NGC 4889. We find that NGC 4889 hosts a central depression in X-ray surface
brightness consistent with a cavity or pair of cavities of radius 0.6 kpc. If
the central cavity is associated with an AGN outburst and contains relativistic
material, its enthalpy should be around 5x10^55 erg. The implied heating power
of this cavity would be around an order of magnitude larger than the energy
lost by X-ray emission. It would be the smallest and youngest known cavity in a
brightest cluster galaxy and the lack of over pressuring implies heating is
still gentle. In contrast, NGC 4874 does not show any evidence for cavities,
although it hosts a well-known wide-angle-tail radio source which is visible
outside the region occupied by the X-ray corona. These two galaxies show that
AGN feedback can behave in varied ways in the same cluster environment.Comment: 11 pages, 11 figures, accepted by MNRA
The cluster Abell 780: an optical view
The Abell 780 cluster, better known as the Hydra A cluster, has been
thouroughly analyzed in X-rays. However, little is known on its optical
properties. We derive the galaxy luminosity function (GLF) in this apparently
relaxed cluster, and search for possible environmental effects by comparing the
GLFs in various regions, and by looking at the galaxy distribution at large
scale around Abell 780. Our study is based on optical images obtained with the
ESO 2.2m telescope and WFI camera in the B and R bands, covering a total region
of 67.22x32.94 arcmin^2, or 4.235x2.075 Mpc^2 for a cluster redshift of 0.0539.
In a region of 500 kpc radius around the cluster centre, the GLF in the R band
shows a double structure, with a broad and flat bright part and a flat faint
end that can be fit by a power law with an index alpha=-0.85+-0.12 in the
20.25<R<21.75 interval. If we divide this 500 kpc radius region in North+South
or East+West halves, we find no clear difference between the GLFs in these
smaller regions. No obvious large scale structure is apparent within 5 Mpc from
the cluster, based on galaxy redshifts and magnitudes collected from the NED
database in a much larger region than that covered by our data, suggesting that
there is no major infall of material in any preferential direction. However,
the Serna-Gerbal method reveals the presence of a gravitationally bound
structure of 27 galaxies, which includes the cD, and of a more strongly
gravitationally bound structure of 14 galaxies. These optical results agree
with the overall relaxed structure of Abell 780 previously derived from X-ray
analyses.Comment: Accepted for publication in Astronomy & Astrophysic
Central galaxy growth and feedback in the most massive nearby cool core cluster
We present multi-wavelength observations of the centre of RXCJ1504.1-0248 -
the galaxy cluster with the most luminous and relatively nearby cool core at
z~0.2. Although there are several galaxies within 100 kpc of the cluster core,
only the brightest cluster galaxy (BCG), which lies at the peak of the X-ray
emission, has blue colours and strong line-emission. Approximately 80 Msun/yr
of intracluster gas is cooling below X-ray emitting temperatures, similar to
the observed UV star formation rate of ~140 Msun/yr. Most star formation occurs
in the core of the BCG and in a 42 kpc long filament of blue continuum, line
emission, and X-ray emission, that extends southwest of the galaxy. The
surrounding filamentary nebula is the most luminous around any observed BCG.
The number of ionizing stars in the BCG is barely sufficient to ionize and heat
the nebula, and the line ratios indicate an additional heat source is needed.
This heat source can contribute to the H\alpha-deduced star formation rates
(SFRs) in BCGs and therefore the derived SFRs should only be considered upper
limits. AGN feedback can slow down the cooling flow to the observed mass
deposition rate if the black hole accretion rate is of the order of 0.5 Msun/yr
at 10% energy output efficiency. The average turbulent velocity of the nebula
is vturb ~325 km/s which, if shared by the hot gas, limits the ratio of
turbulent to thermal energy of the intracluster medium to less than 6%.Comment: 15 pages, 11 figures, MNRAS in press. Corrected typo in abstract
Elastin stabilization of connective tissue
A method and product are provided for the treatment of connective tissue weakened due to destruction of tissue architecture, and in particular due to elastin degradation. The treatment agents employ certain unique properties of phenolic compounds to develop a protocol for reducing elastin degradation, such as that occurring during aneurysm formation in vasculature. According to the invention, elastin can be stabilized in vivo and destruction of connective tissue, such as that leading to life-threatening aneurysms in vasculature, can be tempered or halted all together. The treatment agents can be delivered or administered acutely or chronically according to various delivery methods, including sustained release methods incorporating perivascular or endovascular patches, use of microsphere carriers, hydrogels, or osmotic pumps
On the Merging Cluster Abell 578 and Its Central Radio Galaxy 4C +67.13
Here we analyze radio, optical, and X-ray data for a peculiar cluster Abell
578. This cluster is not fully relaxed and consists of two merging sub-systems.
The brightest cluster galaxy, CGPG 0719.8+6704, is a pair of interacting
ellipticals with projected separation 10 kpc, the brighter of which hosts
the radio source 4C +67.13. The Fanaroff-Riley type-II radio morphology of 4C
+67.13 is unusual for central radio galaxies in local Abell clusters. Our new
optical spectroscopy revealed that both nuclei of the CGPG 0719.8+6704 pair are
active, albeit at low accretion rates corresponding to the Eddington ratio
(for the estimated black hole masses of and ). The gathered X-ray ({\it Chandra})
data allowed us to confirm and to quantify robustly the previously noted
elongation of the gaseous atmosphere in the dominant sub-cluster, as well as a
large spatial offset (\,kpc projected) between the position of the
brightest cluster galaxy and the cluster center inferred from the modeling of
the X-ray surface brightness distribution. Detailed analysis of the brightness
profiles and temperature revealed also that the cluster gas in the vicinity of
4C\,+67.13 is compressed (by a factor of about ) and heated (from
\,keV up to 2.7\,keV), consistent with the presence of a weak shock
(Mach number ) driven by the expanding jet cocoon. This would then
require the jet kinetic power of the order of \,erg\,s,
implying either a very high efficiency of the jet production for the current
accretion rate, or a highly modulated jet/accretion activity in the system.Comment: 12 pages, 11 figures, accepted for publication in Ap
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