1,432 research outputs found
AGN heating and dissipative processes in galaxy clusters
Recent X-ray observations reveal growing evidence for heating by active
galactic nuclei (AGN) in clusters and groups of galaxies. AGN outflows play a
crucial role in explaining the riddle of cooling flows and the entropy problem
in clusters. Here we study the effect of AGN on the intra-cluster medium in a
cosmological simulation using the adaptive mesh refinement FLASH code. We pay
particular attention to the effects of conductivity and viscosity on the
dissipation of weak shocks generated by the AGN activity in a realistic galaxy
cluster. Our 3D simulations demonstrate that both viscous and conductive
dissipation play an important role in distributing the mechanical energy
injected by the AGN, offsetting radiative cooling and injecting entropy to the
gas. These processes are important even when the transport coefficients are at
a level of 10% of the Spitzer value. Provided that both conductivity and
viscosity are suppressed by a comparable amount, conductive dissipation is
likely to dominate over viscous dissipation. Nevertheless, viscous effects may
still affect the dynamics of the gas and contribute a significant amount of
dissipation compared to radiative cooling. We also present synthetic Chandra
observations. We show that the simulated buoyant bubbles inflated by the AGN,
and weak shocks associated with them, are detectable with the Chandra
observatory.Comment: accepted to ApJ, minor change
The Santa Fe Light Cone Simulation Project: I. Confusion and the WHIM in Upcoming Sunyaev-Zel'dovich Effect Surveys
We present the first results from a new generation of simulated large sky
coverage (~100 square degrees) Sunyaev-Zeldovich effect (SZE) cluster surveys
using the cosmological adaptive mesh refinement N-body/hydro code Enzo. We have
simulated a very large (512^3h^{-3}Mpc^3) volume with unprecedented dynamic
range. We have generated simulated light cones to match the resolution and
sensitivity of current and future SZE instruments. Unlike many previous studies
of this type, our simulation includes unbound gas, where an appreciable
fraction of the baryons in the universe reside.
We have found that cluster line-of-sight overlap may be a significant issue
in upcoming single-dish SZE surveys. Smaller beam surveys (~1 arcmin) have more
than one massive cluster within a beam diameter 5-10% of the time, and a larger
beam experiment like Planck has multiple clusters per beam 60% of the time. We
explore the contribution of unresolved halos and unbound gas to the SZE
signature at the maximum decrement. We find that there is a contribution from
gas outside clusters of ~16% per object on average for upcoming surveys. This
adds both bias and scatter to the deduced value of the integrated SZE, adding
difficulty in accurately calibrating a cluster Y-M relationship.
Finally, we find that in images where objects with M > 5x10^{13} M_{\odot}
have had their SZE signatures removed, roughly a third of the total SZE flux
still remains. This gas exists at least partially in the Warm Hot Intergalactic
Medium (WHIM), and will possibly be detectable with the upcoming generation of
SZE surveys.Comment: 14 pages, 13 figures, version accepted to ApJ. Major revisions mad
Challenges for Precision Cosmology with X-ray and Sunyaev-Zeldovich Effect Gas Mass Measurements of Galaxy Clusters
We critically analyze the measurement of galaxy cluster gas masses, which is
central to cosmological studies that rely on the galaxy cluster gas mass
fraction. Using synthetic observations of numerically simulated clusters viewed
through their X-ray emission and thermal Sunyaev-Zeldovich effect (SZE), we
reduce the observations to obtain measurements of the cluster gas mass. We are
thus able to quantify the possible sources of uncertainty and systematic bias
associated with the common simplifying assumptions used in reducing real
cluster observations including isothermality and hydrostatic equilibrium. We
find that intrinsic variations in clusters limit the precision of observational
gas mass estimation to ~10% to 1 sigma confidence excluding instrumental
effects. Gas mass estimates performed via all methods surprisingly show little
or no trending in the scatter as a function of cluster redshift. For the full
cluster sample, methods that use SZE profiles out to roughly the virial radius
are the simplest, most accurate, and unbiased way to estimate cluster mass.
X-ray methods are systematically more precise mass estimators than are SZE
methods if merger and cool core systems are removed, but X-ray methods slightly
overestimate (5-10%) the cluster gas mass on average. We find that cool core
clusters in our samples are particularly poor candidates for observational mass
estimation, even when excluding emission from the core region. The effects of
cooling in the cluster gas alter the radial profile of the X-ray and SZE
surface brightness outside the cool core region, leading to poor gas mass
estimates in cool core clusters. Finally, we find that methods using a
universal temperature profile estimate cluster masses to higher precision than
those assuming isothermality.Comment: 16 pages, 14 figures, Accepted to the Astrophysical Journal major
changes made during refereein
Diffuse radio emission in the galaxy cluster SPT-CL J2031-4037: a steep spectrum intermediate radio halo?
The advent of sensitive low frequency radio observations has revealed a
number of diffuse radio objects with peculiar properties that are challenging
our understanding about the physics of the intracluster medium. Here, we report
the discovery of a steep spectrum radio halo surrounding the central Brightest
Cluster Galaxy (BCG) in the galaxy cluster SPT-CL J2031-4037. This cluster is
morphologically disturbed yet has a weak cool core, an example of cool
core/non-cool core transition system, which harbours a radio halo of
Mpc in size. The halo emission detected at 1.7 GHz is less extended compared to
that in the 325 MHz observation, and the spectral index of the part of the halo
visible at 325 MHz to 1.7 GHz frequencies was found to be .
Also, was found to be W Hz
which falls in the region where radio mini-halos, halo upper limits and
ultra-steep spectrum (USS) halos are found in the plane. Additionally, simulations presented in the paper provide
support to the scenario of the steep spectrum. The diffuse radio emission found
in this cluster may be a steep spectrum "intermediate" or "hybrid" radio halo
which is transitioning into a mini-halo.Comment: 6 pages, 3 figures; Accepted for publication in MNRAS Lette
High sensitivity measurement of 224Ra and 226Ra in water with an improved hydrous titanium oxide technique at the Sudbury Neutrino Observatory
The existing hydrous titanium oxide (HTiO) technique for the measurement of
224Ra and 226Ra in the water at the Sudbury Neutrino Observatory (SNO) has been
changed to make it faster and less sensitive to trace impurities in the HTiO
eluate. Using HTiO-loaded filters followed by cation exchange adsorption and
HTiO co-precipitation, Ra isotopes from 200-450 tonnes of heavy water can be
extracted and concentrated into a single sample of a few millilitres with a
total chemical efficiency of 50%. Combined with beta-alpha coincidence
counting, this method is capable of measuring 2.0x10^3 uBq/kg of 224Ra and
3.7x10^3 uBq/kg of 226Ra from the 232Th and 238U decay chains, respectively,
for a 275 tonne D2O assay, which are equivalent to 5x10^16 g Th/g and 3x10^16 g
U/g in heavy water.Comment: 8 Pages, 2 figures and 2 table
Stirring Up the Pot: Can Cooling Flows In Galaxy Clusters Be Quenched By Gas Sloshing?
X-ray observations of clusters of galaxies reveal the presence of edges in
surface brightness and temperature, known as "cold fronts". In relaxed clusters
with cool cores, these commonly observed edges have been interpreted as
evidence for the "sloshing" of the core gas in the cluster's gravitational
potential. Such sloshing may provide a source of heat to the cluster core by
mixing hot gas from the cluster outskirts with the cool core gas. Using
high-resolution -body/Eulerian hydrodynamics simulations, we model gas
sloshing in galaxy clusters initiated by mergers with subclusters. The
simulations include merger scenarios with gas-filled and gasless subclusters.
The effect of changing the viscosity of the intracluster medium is also
explored. We find that sloshing can facilitate heat inflow to the cluster core,
provided that there is a strong enough disturbance. In adiabatic simulations,
we find that sloshing can raise the entropy floor of the cluster core by nearly
an order of magnitude in the strongest cases. If the ICM is viscous, the mixing
of gases with different entropies is decreased and consequently the heat flux
to the core is diminished. In simulations where radiative cooling is included,
we find that though eventually a cooling flow develops, sloshing can prevent
the significant buildup of cool gas in the core for times on the order of a Gyr
for small disturbances and a few Gyr for large ones. If repeated encounters
with merging subclusters sustain the sloshing of the central core gas as is
observed, this process can provide a relatively steady source of heat to the
core, which can help to prevent a significant cooling flow.Comment: 22 pages, 26 figures, "emulateapj" format. The version accepted by
ApJ, with proof correction
Introduction to Homogenous Catalysis with Ruthenium-Catalyzed Oxidation of Alcohols: An Experiment for Undergraduate Advanced Inorganic Chemistry Students
A three-week laboratory experiment, which introduces students in an advanced inorganic chemistry course to air-sensitive chemistry and catalysis, is described. During the first week, the students synthesize RuCl2(PPh3)3. During the second and third weeks, the students characterize the formed coordination compound and use it as a precatalyst for the oxidation of 1-phenylethanol to acetophenone. The synthesized RuCl2(PPh3)3 is characterized using 1H and 31P NMR spectroscopy, IR spectroscopy, and magnetic susceptibility measurements. The students run catalytic and control reactions and determine the percent yield of the product using 1H NMR. The synthesis and catalytic conditions are modified from previously published research articles. The RuCl2(PPh3)3 complex is air sensitive and is prepared under a nitrogen gas atmosphere and worked up in an inert atmosphere glovebox. The catalytic and control reactions are set up in the inert atmosphere glovebox and carried out at reflux outside of the glovebox under a nitrogen gas atmosphere. In this laboratory, the students learn how to set up and run a reaction under a nitrogen atmosphere, how to work in a glovebox, and how to set up and characterize catalytic and control reactions
The galaxy cluster Ysz-Lx and Ysz-M relations from the WMAP 5-yr data
We use multifrequency matched filters to estimate, in the WMAP 5-year data,
the Sunyaev-Zel'dovich (SZ) fluxes of 893 ROSAT NORAS/REFLEX clusters spanning
the luminosity range Lx,[0.1-2.4]keV = 2 10^{41} - 3.5 10^{45} erg s^{-1}. The
filters are spatially optimised by using the universal pressure profile
recently obtained from combining XMM-Newton observations of the REXCESS sample
and numerical simulations. Although the clusters are individually only
marginally detected, we are able to firmly measure the SZ signal (>10 sigma)
when averaging the data in luminosity/mass bins. The comparison between the
bin-averaged SZ signal versus luminosity and X-ray model predictions shows
excellent agreement, implying that there is no deficit in SZ signal strength
relative to expectations from the X-ray properties of clusters. Using the
individual cluster SZ flux measurements, we directly constrain the Y500-Lx and
Y500-M500 relations, where Y500 is the Compton y-parameter integrated over a
sphere of radius r500. The Y500-M500 relation, derived for the first time in
such a wide mass range, has a normalisation Y*500=[1.60 pm 0.19] 10^{-3}
arcmin^2 at M500=3 10^{14} h^{1} Msun, in excellent agreement with the X-ray
prediction of 1.54 10^{-3} arcmin^2, and a mass exponent of alpha=1.79 pm 0.17,
consistent with the self-similar expectation of 5/3. Constraints on the
redshift exponent are weak due to the limited redshift range of the sample,
although they are compatible with self-similar evolution.Comment: Version accepted for publication in Astronomy and Astrophysic
Observation of single collisionally cooled trapped ions in a buffer gas
Individual Ba ions are trapped in a gas-filled linear ion trap and observed
with a high signal-to-noise ratio by resonance fluorescence. Single-ion storage
times of ~5 min (~1 min) are achieved using He (Ar) as a buffer gas at
pressures in the range 8e-5 - 4e-3 torr. Trap dynamics in buffer gases are
experimentally studied in the simple case of single ions. In particular, the
cooling effects of light gases such as He and Ar and the destabilizing
properties of heavier gases such as Xe are studied. A simple model is offered
to explain the observed phenomenology.Comment: 5 pages, 4 figures, accepted for publication in Phys. Rev. A. Minor
text and figure change
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