119 research outputs found
A Powerful AGN Outburst in RBS 797
Utilizing ks of Chandra X-ray Observatory imaging, we present an
analysis of the intracluster medium (ICM) and cavity system in the galaxy
cluster RBS 797. In addition to the two previously known cavities in the
cluster core, the new and deeper X-ray image has revealed additional structure
associated with the active galactic nucleus (AGN). The surface brightness
decrements of the two cavities are unusually large, and are consistent with
elongated cavities lying close to our line-of-sight. We estimate a total AGN
outburst energy and mean jet power of erg and
erg s, respectively, depending on the
assumed geometrical configuration of the cavities. Thus, RBS 797 is apparently
among the the most powerful AGN outbursts known in a cluster. The average mass
accretion rate needed to power the AGN by accretion alone is
yr. We show that accretion of cold gas onto the AGN at this level is
plausible, but that Bondi accretion of the hot atmosphere is probably not. The
BCG harbors an unresolved, non-thermal nuclear X-ray source with a bolometric
luminosity of erg s. The nuclear emission is
probably associated with a rapidly-accreting, radiatively inefficient accretion
flow. We present tentative evidence that star formation in the BCG is being
triggered by the radio jets and suggest that the cavities may be driving weak
shocks () into the ICM, similar to the process in the galaxy
cluster MS 0735.6+7421.Comment: Accepted to ApJ; 20 pages, 11 low-resolution figure
Abundances of s-process elements in planetary nebulae: Br, Kr & Xe
We identify emission lines of post-iron peak elements in very high
signal-to-noise spectra of a sample of planetary nebulae. Analysis of lines
from ions of Kr and Xe reveals enhancements in most of the PNe, in agreement
with the theories of s-process in AGB star. Surprisingly, we did not detect
lines from Br even though s-process calculations indicate that it should be
produced with Kr at detectable levels.Comment: 2 pages, 1 figure, to be published in the Proceedings of the IAU
Symposium 234: Planetary Nebulae in Our Galaxy and Beyond, eds. M.J. Barlow,
R.H. Mende
A relationship between AGN jet power and radio power
Using Chandra X-ray and VLA radio data, we investigate the scaling
relationship between jet power, P_jet, and synchrotron luminosity, P_rad. We
expand the sample presented in Birzan et al. (2008) to lower radio power by
incorporating measurements for 21 gEs to determine if the Birzan et al. (2008)
P_jet-P_rad scaling relations are continuous in form and scatter from giant
elliptical galaxies (gEs) up to brightest cluster galaxies (BCGs). We find a
mean scaling relation of P_jet approximately 5.8x10^43 (P_rad/10^40)^(0.70)
erg/s which is continuous over ~6-8 decades in P_jet and P_rad with a scatter
of approximately 0.7 dex. Our mean scaling relationship is consistent with the
model presented in Willott et al. (1999) if the typical fraction of lobe energy
in non-radiating particles to that in relativistic electrons is > 100. We
identify several gEs whose radio luminosities are unusually large for their jet
powers and have radio sources which extend well beyond the densest parts of
their X-ray halos. We suggest that these radio sources are unusually luminous
because they were unable to entrain appreciable amounts of gas.Comment: Accepted for publication in the Astrophysical Journal; 8 pages, 3
color figures, 1 tabl
Hot Gas in Galaxy Groups: Recent Observations
Galaxy groups are the least massive systems where the bulk of baryons begin
to be accounted for. Not simply the scaled-down versions of rich clusters
following self-similar relations, galaxy groups are ideal systems to study
baryon physics, which is important for both cluster cosmology and galaxy
formation. We review the recent observational results on the hot gas in galaxy
groups. The first part of the paper is on the scaling relations, including
X-ray luminosity, entropy, gas fraction, baryon fraction and metal abundance.
Compared to clusters, groups have a lower fraction of hot gas around the center
(e.g., r < r_2500), but may have a comparable gas fraction at large radii
(e.g., r_2500 < r < r_500). Better constraints on the group gas and baryon
fractions require sample studies with different selection functions and deep
observations at r > r_500 regions. The hot gas in groups is also iron poor at
large radii (0.3 r_500 - 0.7 r_500). The iron content of the hot gas within the
central regions (r < 0.3 r_500) correlates with the group mass, in contrast to
the trend of the stellar mass fraction. It remains to be seen where the missing
iron in low-mass groups is. In the second part, we discuss several aspects of
X-ray cool cores in galaxy groups, including their difference from cluster cool
cores, radio AGN heating in groups and the cold gas in group cool cores.
Because of the vulnerability of the group cool cores to radio AGN heating and
the weak heat conduction in groups, group cool cores are important systems to
test the AGN feedback models and the multiphase cool core models. At the end of
the paper, some outstanding questions are listed.Comment: 31 pages, 9 figures, to appear in the focus issue on "Galaxy
Clusters", New Journal of Physics,
http://iopscience.iop.org/1367-2630/focus/Focus%20on%20Galaxy%20Cluster
Discrepant Mass Estimates in the Cluster of Galaxies Abell 1689
We present a new mass estimate of a well-studied gravitational lensing
cluster, Abell 1689, from deep Chandra observations with a total exposure of
200 ks. Within r=200 h-1 kpc, the X-ray mass estimate is systematically lower
than that of lensing by 30-50%. At r>200 h-1 kpc, the mass density profiles
from X-ray and weak lensing methods give consistent results. The most recent
weak lensing work suggest a steeper profile than what is found from the X-ray
analysis, while still in agreement with the mass at large radii. Previous
studies have suggested that cooler small-scale structures can bias X-ray
temperature measurements or that the northern part of the cluster is disturbed.
We find these scenarios unlikely to resolve the central mass discrepancy since
the former requires 70-90% of the space to be occupied by these cool structures
and excluding the northern substructure does not significantly affect the total
mass profiles. A more plausible explanation is a projection effect. We also
find that the previously reported high hard-band to broad-band temperature
ratio in A1689, and many other clusters observed with Chandra, may be resulting
from the instrumental absorption that decreases 10-15% of the effective area at
~1.75 keV.Comment: 18 pages, 15 figures. ApJ accepte
A Chandra X-ray Analysis of Abell 1664: Cooling, Feedback and Star Formation in the Central Cluster Galaxy
The brightest cluster galaxy (BCG) in the Abell 1664 cluster is unusually
blue and is forming stars at a rate of ~ 23 M_{\sun} yr^{-1}. The BCG is
located within 5 kpc of the X-ray peak, where the cooling time of 3.5x10^8 yr
and entropy of 10.4 keV cm^2 are consistent with other star-forming BCGs in
cooling flow clusters. The center of A1664 has an elongated, "bar-like" X-ray
structure whose mass is comparable to the mass of molecular hydrogen, ~ 10^{10}
M_{\sun} in the BCG. We show that this gas is unlikely to have been stripped
from interloping galaxies. The cooling rate in this region is roughly
consistent with the star formation rate, suggesting that the hot gas is
condensing onto the BCG. We use the scaling relations of Birzan et al. 2008 to
show that the AGN is underpowered compared to the central X-ray cooling
luminosity by roughly a factor of three. We suggest that A1664 is experiencing
rapid cooling and star formation during a low-state of an AGN feedback cycle
that regulates the rates of cooling and star formation. Modeling the emission
as a single temperature plasma, we find that the metallicity peaks 100 kpc from
the X-ray center, resulting in a central metallicity dip. However, a
multi-temperature cooling flow model improves the fit to the X-ray emission and
is able to recover the expected, centrally-peaked metallicity profile.Comment: 15 pages, 13 figure
Non-parametric modeling of the intra-cluster gas using APEX-SZ bolometer imaging data
We demonstrate the usability of mm-wavelength imaging data obtained from the
APEX-SZ bolometer array to derive the radial temperature profile of the hot
intra-cluster gas out to radius r_500 and beyond. The goal is to study the
physical properties of the intra-cluster gas by using a non-parametric
de-projection method that is, aside from the assumption of spherical symmetry,
free from modeling bias. We use publicly available X-ray imaging data from the
XMM-Newton observatory and our Sunyaev-Zel'dovich Effect (SZE) imaging data
from the APEX-SZ experiment at 150 GHz to de-project the density and
temperature profiles for the relaxed cluster Abell 2204. We derive the gas
density, temperature and entropy profiles assuming spherical symmetry, and
obtain the total mass profile under the assumption of hydrostatic equilibrium.
For comparison with X-ray spectroscopic temperature models, a re-analysis of
the recent Chandra observation is done with the latest calibration updates.
Using the non-parametric modeling we demonstrate a decrease of gas temperature
in the cluster outskirts, and also measure the gas entropy profile. These
results are obtained for the first time independently of X-ray spectroscopy,
using SZE and X-ray imaging data. The contribution of the SZE systematic
uncertainties in measuring T_e at large radii is shown to be small compared to
the Chandra systematic spectroscopic errors. The upper limit on M_200 derived
from the non-parametric method is consistent with the NFW model prediction from
weak lensing analysis.Comment: Replaced with the published version; A&A 519, A29 (2010
A Spectacular Bow Shock in the 11 keV Galaxy Cluster Around 3C 438
This is a pre-copyedited, author-produced pdf of an article accepted for publication in The Astrophysical Journal following peer review. The version of record, Deanna L. Emery; Ăkos BogdĂĄn; Ralph P. Kraft; Felipe Andrade-Santos; William R. Forman; Martin Hardcastle; and Christine Jones, âA spectacular bow shock in the 11 keV galaxy cluster around 3C 438â, The Astrophysical Journal (2017) 834(2):159 (7pp), published 10 January 2017, is available at doi: 10.3847/1538-4357/834/2/159 © 2017. The American Astronomical Society. All rights reserved.We present results of deep 153 ks Chandra observations of the hot, 11 keV, galaxy cluster associated with the radio galaxy 3C 438. By mapping the morphology of the hot gas and analyzing its surface brightness and temperature distributions, we demonstrate the presence of a merger bow shock. We identify the presence of two jumps in surface brightness and in density located at 400 kpc and 800 kpc from the cluster's core. At the position of the inner jump, we detect a factor of density jump, while at the location of the outer jump, we detect a density drop of a factor of . Combining this with the temperature distribution within the cluster, we establish that the pressure of the hot gas is continuous at the 400 kpc jump, while there is a factor of pressure discontinuity at 800 kpc jump. From the magnitude of the outer pressure discontinuity, using the Rankine-Hugoniot jump conditions, we determine that the sub-cluster is moving at , or approximately km/s through the surrounding intracluster medium, creating the conditions for a bow shock. Based on these findings, we conclude that the pressure discontinuity is likely the result of an ongoing major merger between two massive clusters. Since few observations of bow shocks in clusters have been made, this detection can contribute to the study of the dynamics of cluster mergers, which offers insight on how the most massive clusters may have formed.Peer reviewe
2-D Magnetohydrodynamic Simulations of Induced Plasma Dynamics in the Near-Core Region of a Galaxy Cluster
We present results from numerical simulations of the cooling-core cluster
A2199 produced by the two-dimensional (2-D) resistive magnetohydrodynamics
(MHD) code MACH2. In our simulations we explore the effect of anisotropic
thermal conduction on the energy balance of the system. The results from
idealized cases in 2-D axisymmetric geometry underscore the importance of the
initial plasma density in ICM simulations, especially the near-core values
since the radiation cooling rate is proportional to . Heat conduction
is found to be non-effective in preventing catastrophic cooling in this
cluster. In addition we performed 2-D planar MHD simulations starting from
initial conditions deliberately violating both thermal balance and hydrostatic
equilibrium in the ICM, to assess contributions of the convective terms in the
energy balance of the system against anisotropic thermal conduction. We find
that in this case work done by the pressure on the plasma can dominate the
early evolution of the internal energy over anisotropic thermal conduction in
the presence of subsonic flows, thereby reducing the impact of the magnetic
field. Deviations from hydrostatic equilibrium near the cluster core may be
associated with transient activity of a central active galactic nucleus and/or
remnant dynamical activity in the ICM and warrant further study in three
dimensions.Comment: 16 pages, 13 figures, accepted for publication in MNRA
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