7,537 research outputs found
XMM-Newton observations of three poor clusters: Similarity in dark matter and entropy profiles down to low mass
(Abridged) We present an analysis of the mass and entropy profiles of three
poor clusters (A1991, A2717 and MKW9) observed with XMM-Newton. The clusters
have similar temperatures (kT=2.65, 2.53 and 2.58 keV), and similar redshifts
(0.04 < z < 0.06). We trace the surface brightness, temperature, entropy and
integrated mass profiles up to 0.5 (0.35 for MKW9) of the virial radius
(r_200). The integrated mass profiles are very similar in physical units and
are reasonably well fitted with the NFW mass model with concentration
parameters of c_200=4-6 and M_200=1.2-1.6 X 10^14 h_70^-1 \msun. The entropy
profiles are similar at large scale, but there is some scatter in the central
region (r<50 kpc). None of the clusters has an isentropic core. Including XMM
data on A1983 (kT=2.2 keV), and A1413 (kT = 6.5 keV), we discuss the structural
and scaling properties of cluster mass and entropy profiles. The scaled mass
profiles display <20% dispersion in the 0.05 - 0.5 r_200 radial range. The
c_200 parameters of these clusters, and other values from the literature, are
fully consistent with the c_200 - M_200 relation derived from simulations. The
dispersion in scaled entropy profiles is small, implying self-similarity down
to low mass (kT ~2 keV), and is reduced by 30-40% (to ~20%) if we use the
empirical relation S \propto T^0.65 instead of the standard self-similar
relation, S \propto T. The mean scaled profile is well fitted by a power law
for 0.05 < r_200 < 0.5, with a slope slightly lower than expected from pure
shock heating (\alpha = 0.94+/-0.14), and a normalisation at 0.1 r_200
consistent with previous studies. The gas history thus likely depends both on
gravitational processes and the interplay between cooling and various galaxy
feedback mechanisms.Comment: Final refereed version to appear in A&A. Minor changes. 15 pages, 12
figures (Figs 1 & 3 low res
X-ray observations of the mass and entropy distributions in nearby galaxy clusters
I review some important aspects of the structural and statistical properties
of the nearby X-ray galaxy cluster population, discussing the new constraints
on mass profiles, the mass-temperature relation, and the entropy of the
intracluster medium which have become available from recent X-ray observations.Comment: 11 pages, 4 figures. Invited review to appear in the proceedings of
the XLIst Rencontres de Moriond, XXVIth Astrophysics Moriond Meeting: "From
dark halos to light", Eds. L.Tresse, S. Maurogordato and J. Tran Thanh Van.
Typos corrected, added reference
Causality Violations in Cascade Models of Nuclear Collisions
Transport models have successfully described many aspects of intermediate
energy heavy-ion collision dynamics. As the energies increase in these models
to the ultrarelativistic regime, Lorentz covariance and causality are not
strictly respected. The standard argument is that such effects are not
important to final results; but they have not been seriously considered at high
energies. We point out how and why these happen, how serious of a problem they
may be and suggest ways of reducing or eliminating the undesirable effects.Comment: RevTeX, 23 pages, 9 (uuencoded) figures; to appear in Phys. Rev
Calibration of the galaxy cluster M_500-Y_X relation with XMM-Newton
The quantity Y_ X, the product of the X-ray temperature T_ X and gas mass M_
g, has recently been proposed as a robust low-scatter mass indicator for galaxy
clusters. Using precise measurements from XMM-Newton data of a sample of 10
relaxed nearby clusters, spanning a Y_ X range of 10^13 -10^15 M_sun keV, we
investigate the M_500-Y_ X relation. The M_500 - Y_ X data exhibit a power law
relation with slope alpha=0.548 \pm 0.027, close to the self-similar value
(3/5) and independent of the mass range considered. However, the normalisation
is \sim 20% below the prediction from numerical simulations including cooling
and galaxy feedback. We discuss two effects that could contribute to the
normalisation offset: an underestimate of the true mass due to the HE
assumption used in X-ray mass estimates, and an underestimate of the hot gas
mass fraction in the simulations. A comparison of the functional form and
scatter of the relations between various observables and the mass suggest that
Y_ X may indeed be a better mass proxy than T_ X or M_g,500.Comment: 4 pages, 2 figures, accepted for publication in A&
The hot gas content of fossil galaxy clusters
We investigate the properties of the hot gas in four fossil galaxy systems
detected at high significance in the Planck Sunyaev-Zeldovich (SZ) survey.
XMM-Newton observations reveal overall temperatures of kT ~ 5-6 keV and yield
hydrostatic masses M500,HE > 3.5 x 10e14 Msun, confirming their nature as bona
fide massive clusters. We measure the thermodynamic properties of the hot gas
in X-rays (out to beyond R500 in three cases) and derive their individual
pressure profiles out to R ~ 2.5 R500 with the SZ data. We combine the X-ray
and SZ data to measure hydrostatic mass profiles and to examine the hot gas
content and its radial distribution. The average Navarro-Frenk-White (NFW)
concentration parameter, c500 = 3.2 +/- 0.4, is the same as that of relaxed
`normal' clusters. The gas mass fraction profiles exhibit striking variation in
the inner regions, but converge to approximately the cosmic baryon fraction
(corrected for depletion) at R500. Beyond R500 the gas mass fraction profiles
again diverge, which we interpret as being due to a difference in gas clumping
and/or a breakdown of hydrostatic equilibrium in the external regions. Overall
our observations point to considerable radial variation in the hot gas content
and in the gas clumping and/or hydrostatic equilibrium properties in these
fossil clusters, at odds with the interpretation of their being old, evolved
and undisturbed. At least some fossil objects appear to be dynamically young.Comment: 4 pages, 2 figures. Accepted for publication in A&
Investigating the hard X-ray emission from the hottest Abell cluster A2163 with Suzaku
We present the results from Suzaku observations of the hottest Abell galaxy
cluster A2163 at . To study the physics of gas heating in cluster
mergers, we investigated hard X-ray emission from the merging cluster A2163,
which hosts the brightest synchrotron radio halo. We analyzed hard X-ray
spectra accumulated from two-pointed Suzaku observations. Non-thermal hard
X-ray emission should result from the inverse Compton (IC) scattering of
relativistic electrons by the CMB photons. To measure this emission, the
dominant thermal emission in the hard X-ray band must be modeled in detail. To
this end, we analyzed the combined broad-band X-ray data of A2163 collected by
Suzaku and XMM-Newton, assuming single- and multi-temperature models for
thermal emission and the power-law model for non-thermal emission. From the
Suzaku data, we detected significant hard X-ray emission from A2163 in the
12-60 keV band at the level (or at the level if a
systematic error is considered). The Suzaku HXD spectrum alone is consistent
with the single-T thermal model of gas temperature keV. From the XMM
data, we constructed a multi-T model including a very hot ( keV)
component in the NE region. Incorporating the multi-T and the power-law models
into a two-component model with a radio-band photon index, the 12-60 keV energy
flux of non-thermal emission is constrained within . The 90% upper limit of detected IC
emission is marginal ( in the
12-60 keV). The estimated magnetic field in A2163 is .
While the present results represent a three-fold increase in the accuracy of
the broad band spectral model of A2163, more sensitive hard X-ray observations
are needed to decisively test for the presence of hard X-ray emission due to IC
emission.Comment: 7 pages, 7 figures, A&A accepted. Minor correctio
Joint measurement of the galaxy cluster pressure profile with Planck and SPT-SZ
We measured the average Compton profile of 461 clusters detected jointly by
the South Pole Telescope (SPT) and Planck. The number of clusters included in
this analysis is about one order of magnitude larger than in previous analyses.
We propose an innovative method developed in Fourier space to combine optimally
the Planck and SPT-SZ data, allowing us to perform a clean deconvolution of the
point spread and transfer functions while simultaneously rescaling by the
characteristic radial scale with respect to the critical density.
The method additionally corrects for the selection bias of SPT clusters in the
SPT-SZ data. We undertake a generalised Navarro-Frenk-White (NFW) fit to the
profile with only one parameter fixed, allowing us to constrain the other four
parameters with excellent precision. The best-fitting profile is in good
agreement with the Universal Pressure Profile based on REXCESS in the inner
region and with the Planck Intermediate Paper V profile based on Planck and the
XMM archive in the outer region. We investigate trends with redshift and mass,
finding no indication of redshift evolution but detecting a significant
difference in the pressure profile of the low vs. high mass subsamples, in the
sense that the low mass subsample has a profile that is more centrally-peaked
than that of the high mass subsample. [abridged]Comment: 15 pages, 12 figures, submitted to A&
Sensitivity of Ag/Al Interface Specific Resistances to Interfacial Intermixing
We have measured an Ag/Al interface specific resistance, 2AR(Ag/Al)(111) =
1.4 fOhm-m^2, that is twice that predicted for a perfect interface, 50% larger
than for a 2 ML 50%-50% alloy, and even larger than our newly predicted 1.3
fOhmm^2 for a 4 ML 50%-50% alloy. Such a large value of 2ARAg/Al(111) confirms
a predicted sensitivity to interfacial disorder and suggests an interface
greater than or equal to 4 ML thick. From our calculations, a predicted
anisotropy ratio, 2AR(Ag/Al)(001)/2AR(Ag/Al)(111), of more then 4 for a perfect
interface, should be reduced to less than 2 for a 4 ML interface, making it
harder to detect any such anisotropy.Comment: 3 pages, 2 figures, 1 table. In Press: Journal of Applied Physic
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