465 research outputs found
A Uniform Contribution of Core-Collapse and Type Ia Supernovae to the Chemical Enrichment Pattern in the Outskirts of the Virgo Cluster
We present the first measurements of the abundances of -elements (Mg,
Si, and S) extending out to beyond the virial radius of a cluster of galaxies.
Our results, based on Suzaku Key Project observations of the Virgo Cluster,
show that the chemical composition of the intra-cluster medium is consistent
with being constant on large scales, with a flat distribution of the Si/Fe,
S/Fe, and Mg/Fe ratios as a function of radius and azimuth out to 1.4 Mpc (1.3
). Chemical enrichment of the intergalactic medium due solely to core
collapse supernovae (SNcc) is excluded with very high significance; instead,
the measured metal abundance ratios are generally consistent with the Solar
value. The uniform metal abundance ratios observed today are likely the result
of an early phase of enrichment and mixing, with both SNcc and type Ia
supernovae (SNIa) contributing to the metal budget during the period of peak
star formation activity at redshifts of 2-3. We estimate the ratio between the
number of SNIa and the total number of supernovae enriching the intergalactic
medium to be between 12-37%, broadly consistent with the metal abundance
patterns in our own Galaxy or with the SNIa contribution estimated for the
cluster cores.Comment: accepted for publication in ApJ
An azimuthally resolved study of the cold front in Abell 3667
The microphysical properties, such as effective viscosity and conductivity, of the weakly magnetized intergalactic plasma are not yet well known. We investigate the constraints that can be placed by an azimuthally resolved study of the cold front in Abell 3667 using similar to 500 ks archival Chandra data. We find that the radius of the interface fluctuates with position angle and the morphology of the interface is strikingly similar to recent numerical simulations of inviscid gas-stripping. We find multiple edges in the surface brightness profiles across the cold front as well as azimuthal variations, which are consistent with the presence of Kelvin-Helmholtz instabilities (KHIs) developing along the cold front. They indicate that the characteristic length-scale of KHI rolls is around 20-80 kpc. This is the first observational indication of developing KHIs along a merger cold front in a galaxy cluster. Based on the KHI scenario, we estimated the upper limit of the intracluster medium effective viscosity. The estimated value of mu less than or similar to 200 g cm(-1) s(-1) is at most 5 per cent of the isotropic Spitzer-like viscosity. The observed apparent mixing towards the outer edges away from the tip of the front provides an additional evidence for suppressed viscosity
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
Substructures in the core of Abell 2319
We analysed the deep archival Chandra observations of the high-temperature
galaxy cluster Abell 2319 to investigate the prominent cold front in its core.
The main sharp arc of the front shows wiggles, or variations of the radius of
the density jump along the arc. At the southern end of the arc is a feature
that resembles a Kelvin-Helmholtz (KH) eddy, beyond which the sharp front
dissolves. These features suggest that KH instabilities develop at the front.
Under this assumption, we can place an upper limit on the ICM viscosity that is
several times below the isotropic Spitzer value. Other features include a split
of the cold front at its northern edge, which may be another KH eddy. There is
a small pocket of hot, less-dense gas inside the cold front, which may indicate
a `hole' in the front's magnetic insulation layer that lets the heat from the
outer gas to penetrate inside the front. Finally, a large concave brightness
feature southwest of the cluster core can be caused by the gasdynamic
instabilities. We speculate that it can also be an inner boundary of a giant
AGN bubble, similar to that in Ophiuchus. If the latter interpretation is
supported by better radio data, this could be a remnant of another extremely
powerful AGN outburst.Comment: Accepted for publication in MNRA
Deep Chandra observation and numerical studies of the nearest cluster cold front in the sky
We present the results of a very deep (500 ks) Chandra observation, along with tailored numerical simulations, of the nearest, best resolved cluster cold front in the sky, which lies 90 kpc (19 arcmin) to the north-west of M 87. The northern part of the front appears the sharpest, with a width smaller than 2.5 kpc (1.5 Coulomb mean free paths; at 99 per cent confidence). Everywhere along the front, the temperature discontinuity is narrower than 4â8 kpc and the metallicity gradient is narrower than 6 kpc, indicating that diffusion, conduction and mixing are suppressed across the interface. Such transport processes can be naturally suppressed by magnetic fields aligned with the cold front. Interestingly, comparison to magnetohydrodynamic simulations indicates that in order to maintain the observed sharp density and temperature discontinuities, conduction must also be suppressed along the magnetic field lines. However, the northwestern part of the cold front is observed to have a non-zero width. While other explanations are possible, the broadening is consistent with the presence of KelvinâHelmholtz instabilities (KHI) on length-scales of a few kpc. Based on comparison with simulations, the presence of KHI would imply that the effective viscosity of the intracluster medium is suppressed by more than an order of magnitude with respect to the isotropic Spitzer-like temperature dependent viscosity. Underneath the cold front, we observe quasi-linear features that are âŒ10 per cent brighter than the surrounding gas and are separated by âŒ15 kpc from each other in projection. Comparison to tailored numerical simulations suggests that the observed phenomena may be due to the amplification of magnetic fields by gas sloshing in wide layers below the cold front, where the magnetic pressure reaches âŒ5â10 per cent of the thermal pressure, reducing the gas density between the bright features
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