681 research outputs found
XMM-Newton observation of the relaxed cluster A478: gas and dark matter distribution from 0.01 R_200 to 0.5 R_200
We present an \xmm mosaic observation of the hot ( keV) and nearby
() relaxed cluster of galaxies A478. We derive precise gas density,
gas temperature, gas mass and total mass profiles up to 12\arcmin (about half
of the virial radius ). The gas density profile is highly peaked
towards the center and the surface brightness profile is well fitted by a sum
of three --models. The derived gas density profile is in excellent
agreement, both in shape and in normalization, with the published Chandra
density profile (measured within 5\arcmin of the center). Projection and PSF
effects on the temperature profile determination are thoroughly investigated.
The derived radial temperature structure is as expected for a cluster hosting a
cooling core, with a strong negative gradient at the cluster center. The
temperature rises from keV up to a plateau of keV beyond 2'
(i.e. , Mpc being the virial radius).
From the temperature profile and the density profile and under the hypothesis
of hydrostatic equilibrium, we derived the total mass profile of A478 down to
0.01 and up to 0.5 the virial radius. We tested different dark matter models
against the observed mass profile. The Navarro, Frenk & White
(\cite{navarro97}) model is significantly preferred to other models. It leads
to a total mass of M for a concentration
parameter of . The gas mass fraction slightly increases with
radius. The gas mass fraction at a density contrast of is
\fgas=0.13\pm0.02, consistent with previous results on similar hot and
massive clusters. We confirm the excess of absorption in the direction of
A478.[abridged]Comment: 15 pages, 11 figures, accepted for publication in A&A, corrected
typo
X-ray Constraints on the Intrinsic Shape of the Lenticular Galaxy NGC 1332
We have analyzed ROSAT PSPC X-ray data of the optically elongated S0 galaxy
NGC 1332 with the purposes of constraining the intrinsic shape of its
underlying mass and presenting a detailed investigation of the uncertainties
resulting from the assumptions underlying this type of analysis. The X-ray
isophotes are elongated with ellipticity (90% confidence) for
semi-major axes 75\arcsec -90\arcsec and have orientations consistent with
the optical isophotes (ellipticity ). The spectrum is poorly
constrained by the PSPC data and cannot rule out sizeable radial temperature
gradients or an emission component due to discrete sources equal in magnitude
to the hot gas. Using (and clarifying) the "geometric test" for dark matter, we
determined that the hypothesis that mass-traces-light is not consistent with
the X-ray data at 68% confidence and marginally consistent at 90% confidence
independent of the gas temperature profile. Detailed modeling gives constraints
on the ellipticity of the underlying mass of \epsilon_{mass} = 0.47 - 0.72
(0.31 - 0.83) at 68% (90%) confidence for isothermal and polytropic models. The
total mass of the isothermal models within a=43.6 kpc (D = 20h^{-1}_{80} Mpc)
is M_{tot} = (0.38 - 1.7) \times 10^{12}M_{\sun} (90% confidence) corresponding
to total blue mass-to-light ratio \Upsilon_B = (31.9 - 143) \Upsilon_{\sun}.
Similar results are obtained when the dark matter is fit directly using the
known distributions of the stars and gas. When possible rotation of the gas and
emission from discrete sources are included flattened mass distributions are
still required, although the constraints on \epsilon_{mass}$, but not the
total mass, are substantially weakened.Comment: 45 pages (figures missing), PostScript, to appear in ApJ on January
20, 199
Mass Models and Sunyaev-Zeldovich Effect Predictions for a Flux Limited Sample of 22 Nearby X-Ray Clusters
We define a 90% complete, volume-limited sample of 31 z<0.1 x-ray clusters
and present a systematic analysis of public ROSAT PSPC data on 22 of these
objects. Our efforts are undertaken in support of the Penn/OVRO SZE survey, and
to this end we present predictions for the inverse Compton optical depth
towards all 22 of these clusters. We have performed detailed Monte Carlo
simulations to understand the effects of the cluster profile uncertainties on
the SZE predictions given the OVRO 5.5-meter telescope beam and switching
patterns; we find that the profile uncertainties are one of the least
significant components of our error budget for SZE-based distance measurements.
We also present baryonic masses and baryon mass fractions derived under the
assumption of hydrostatic equilibrium for these 22 clusters. The mean baryonic
mass fraction within R_500 \sim 500 h^-1 kpc is (7.02 \pm 0.28) x 10^-2 h^-3/2,
or (19.8 \pm 0.8) x 10^-2 for h=0.5. We confirm the Allen et al. (1993) claim
of an excess absorbing column density towards Abell 478, but do not find
similar anomalies in the other 21 clusters in our sample. We also find some
evidence for an excess of soft counts in the ROSAT PSPC data.
A measurement of H_o using these models and OVRO SZE determinations will be
presented in a second paper.Comment: 51 pages, 6 figures included in text. Added comparison of different
cosmologies; accepted for publication in Ap
Chandra Observation of Abell 2142: Survival of Dense Subcluster Cores in a Merger
We use Chandra data to map the gas temperature in the central region of the
merging cluster A2142. The cluster is markedly nonisothermal; it appears that
the central cooling flow has been disturbed but not destroyed by a merger. The
X-ray image exhibits two sharp, bow-shaped, shock-like surface brightness edges
or gas density discontinuities. However, temperature and pressure profiles
across these edges indicate that these are not shock fronts. The pressure is
reasonably continuous across these edges, while the entropy jumps in the
opposite sense to that in a shock (i.e. the denser side of the edge has lower
temperature, and hence lower entropy). Most plausibly, these edges delineate
the dense subcluster cores that have survived a merger and ram pressure
stripping by the surrounding shock-heated gas.Comment: Latex, 9 pages, 5 figures (including color), uses emulateapj.sty.
Submitted to Ap
ASCA Temperature Maps of Three Clusters of Galaxies Abell 1060, AWM7, and the Centaurus Cluster
We present two-dimensional temperature maps of three bright clusters of
galaxies Abell 1060, AWM7, and the Centaurus cluster, based on multi-pointing
observations with the ASCA GIS. The temperatures are derived from hardness
ratios by taking into account the XRT response. For the Centaurus cluster, we
subtracted the central cool component using the previous ASCA and ROSAT
results, and the metallicity gradients observed in AWM7 and the Centaurus
cluster were included in deriving the temperatures. The intracluster medium in
Abell 1060 and AWM7 is almost isothermal from the center to outer regions with
a temperature of 3.3 and 3.9 keV, respectively. The Centaurus cluster exhibits
remarkable hot regions within about 30' from the cluster center showing a
temperature increase of +0.8 keV from the surrounding level of 3.5 keV, and
outer cool regions with lower temperatures by -1.3 keV. These results imply
that a strong merger has occurred in the Centaurus in the recent 2-3 Gyr, and
the central cool component has survived it. In contrast, the gas in Abell 1060
was well-mixed in an early period, which probably has prevented the development
of the central cool component. In AWM7, mixing of the gas should have occurred
in a period earlier than the epoch of metal enrichment.Comment: 18 pages, 8 figures (including color), Latex(PASJadd.sty,
PASJ95.sty), accepted for publication in PASJ. Postscript is also available
at http://www-x.phys.metro-u.ac.jp/~furusho/papers.htm
Cosmological Effects of Powerful AGN Outbursts in Galaxy Clusters: Insights from an XMM-Newton Observation of MS0735+7421
We report on the results of an analysis of XMM-Newton observations of
MS0735+7421, the galaxy cluster which hosts the most energetic AGN outburst
currently known. The previous Chandra image shows twin giant X-ray cavities
(~200 kpc diameter) filled with radio emission and surrounded by a weak shock
front. XMM data are consistent with these findings. The total energy in
cavities and shock (~6 \times 10^{61} erg) is enough to quench the cooling flow
and, since most of the energy is deposited outside the cooling region (~100
kpc), to heat the gas within 1 Mpc by ~1/4 keV per particle. The cluster
exhibits an upward departure (factor ~2) from the mean L-T relation. The boost
in emissivity produced by the ICM compression in the bright shells due to the
cavity expansion may contribute to explain the high luminosity and high central
gas mass fraction that we measure. The scaled temperature and metallicity
profiles are in general agreement with those observed in relaxed clusters.
Also, the quantities we measure are consistent with the observed M-T relation.
We conclude that violent outbursts such as the one in MS0735+7421 do not cause
dramatic instantaneous departures from cluster scaling relations (other than
the L-T relation). However, if they are relatively common they may play a role
in creating the global cluster properties.Comment: 69 pages, 30 figures, accepted for publication in ApJ Main Journa
Witnessing the Growth of the Nearest Galaxy Cluster: Thermodynamics of the Virgo Cluster Outskirts
We present results from Suzaku Key Project observations of the Virgo Cluster,
the nearest galaxy cluster to us, mapping its X-ray properties along four long
`arms' extending beyond the virial radius. The entropy profiles along all four
azimuths increase with radius, then level out beyond , while the
average pressure at large radii exceeds Planck Sunyaev-Zel'dovich measurements.
These results can be explained by enhanced gas density fluctuations (clumping)
in the cluster's outskirts. Using a standard Navarro, Frenk and White (1997)
model, we estimate a virial mass, radius, and concentration parameter of
M, kpc, and , respectively. The inferred cumulative baryon fraction exceeds
the cosmic mean at along the major axis, suggesting enhanced
gas clumping possibly sourced by a candidate large-scale structure filament
along the north-south direction. The Suzaku data reveal a large-scale sloshing
pattern, with two new cold fronts detected at radii of 233 kpc and 280 kpc
along the western and southern arms, respectively. Two high-temperature regions
are also identified 1 Mpc towards the south and 605 kpc towards the west of
M87, likely representing shocks associated with the ongoing cluster growth.
Although systematic uncertainties in measuring the metallicity for low
temperature plasma remain, the data at large radii appear consistent with a
uniform metal distribution on scales of kpc and larger,
providing additional support for the early chemical enrichment scenario driven
by galactic winds at redshifts of 2-3.Comment: submitted to MNRA
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