2,598 research outputs found
Systematic Errors in the Hubble Constant Measurement from the Sunyaev-Zel'dovich effect
The Hubble constant estimated from the combined analysis of the
Sunyaev-Zel'dovich effect and X-ray observations of galaxy clusters is
systematically lower than those from other methods by 10-15 percent. We examine
the origin of the systematic underestimate using an analytic model of the
intracluster medium (ICM), and compare the prediction with idealistic triaxial
models and with clusters extracted from cosmological hydrodynamical
simulations. We identify three important sources for the systematic errors;
density and temperature inhomogeneities in the ICM, departures from
isothermality, and asphericity. In particular, the combination of the first two
leads to the systematic underestimate of the ICM spectroscopic temperature
relative to its emission-weighed one. We find that these three systematics well
reproduce both the observed bias and the intrinsic dispersions of the Hubble
constant estimated from the Sunyaev-Zel'dovich effect.Comment: 26 pages, 7 figures, accepted for publication in ApJ, Minor change
L_X-T Relation and Related Properties of Galaxy Clusters
An observational approach is presented to constrain the global structure and
evolution of the intracluster medium based on the ROSAT and ASCA distant
cluster sample. From statistical analysis of the gas density profile and the
connection to the LX-T relation under the beta-model, the scaled gas profile is
nearly universal for the outer region and the LX(>0.2r500) is tightly related
to the temperature through T^3 rather than T^2. On the other hand, a large
density scatter exists in the core region and there is clearly a deviation from
the self-similar scaling for clusters with a small core size. A direct link
between the core size and the radiative cooling timescale suggest that t_cool
is a parameter to control the gas structure and the appearance of small cores
in regular clusters may be much connected with the thermal evolution. We derive
the luminosity-ambient temperature (T') relation, assuming the universal
temperature profile to find the dispersion around the relation significantly
decreases: L_1keV is almost constant for a wide range of t_cool. We further
examined the LX-Tbeta and LX-T'beta relations and showed a trend that merging
clusters segregate from the regular clusters on the planes. A good correlation
between t_cool and the X-ray morphology on the L_1keV-t_cool/t_age plane leads
us to define three phases according to the different level of cooling, and draw
a phenomenological picture: after a cluster collapses and t_cool falls below
t_age, the core cools radiatively with quasi-hydrostatic balancing in the
gravitational potential, and the central density gradually becomes higher to
evolve from an outer-core-dominant cluster to inner-core-dominant cluster.Comment: 39 pages, 37 figures. Accepted for publication in ApJ. Version with
high-quality color figures at
http://cosmic.riken.jp/ota/publications/index.htm
Constraints on Primordial Nongaussiantiy from the High-Redshift Cluster MS1054--03
The implications of the massive, X-ray selected cluster of galaxies
MS1054--03 at are discussed in light of the hypothesis that the
primordial density fluctuations may be nongaussian. We generalize the
Press-Schechter (PS) formalism to the nongaussian case, and calculate the
likelihood that a cluster as massive as MS1054 would appear in the EMSS. The
probability of finding an MS1054-like cluster depends only on \omegam and the
extent of primordial nongaussianity. We quantify the latter by adopting a
specific functional form for the PDF, denoted which tends to
Gaussianity for and show how is related to the more
familiar statistic the probability of fluctuations for a
given PDF relative to a Gaussian. We find that Gaussian initial density
fluctuations are consistent with the data on MS1054 only if \omegam\simlt
0.2. For \omegam\ge 0.25 a significant degree of nongaussianity is required,
unless the mass of MS1054 has been substantially overestimated by X-ray and
weak lensing data. The required amount of nongaussianity is a rapidly
increasing function of \omegam for 0.25 \le \omegam \le 0.45, with (T \simgt 7) at the upper end of this range. For a fiducial
\omegam=0.3, \omegal=0.7 universe, favored by several lines of evidence we
obtain an upper limit corresponding to a This
finding is consistent with the conclusions of Koyama, Soda, & Taruya (1999),
who applied the generalized PS formalism to low (z\simlt 0.1) and
intermediate (z\simlt 0.6) redshift cluster data sets.Comment: 15 pages, 11 figures, submitted to the Astrophysical Journal, uses
emulateapj.st
Synthesis, Structure, and Ferromagnetism of a New Oxygen Defect Pyrochlore System Lu2V2O_{7-x} (x = 0.40-0.65)
A new fcc oxygen defect pyrochlore structure system Lu2V2O_{7-x} with x =
0.40 to 0.65 was synthesized from the known fcc ferromagnetic semiconductor
pyrochlore compound Lu2V2O7 which can be written as Lu2V2O6O' with two
inequivalent oxygen sites O and O'. Rietveld x-ray diffraction refinements
showed significant Lu-V antisite disorder for x >= 0.5. The lattice parameter
versus x (including x = 0) shows a distinct maximum at x ~ 0.4. We propose that
these observations can be explained if the oxygen defects are on the O'
sublattice of the structure. The magnetic susceptibility versus temperature
exhibits Curie-Weiss behavior above 150 K for all x, with a Curie constant C
that increases with x as expected in an ionic model. However, the magnetization
measurements also show that the (ferromagnetic) Weiss temperature theta and the
ferromagnetic ordering temperature T_C both strongly decrease with increasing x
instead of increasing as expected from C(x). The T_C decreases from 73 K for x
= 0 to 21 K for x = 0.65. Furthermore, the saturation moment at a field of 5.5
T at 5 K is nearly independent of x, with the value expected for a fixed spin
1/2 per V. The latter three observations suggest that Lu2V2O_{7-x} may contain
localized spin 1/2 vanadium moments in a metallic background that is induced by
oxygen defect doping, instead of being a semiconductor as suggested by the C(x)
dependence.Comment: 9 pages including 7 figures, 3 table
Chandra observtaion of A2256 - a cluster at the early stage of merging
We present here \chandra observations of the rich cluster of galaxies A2256.
In addition to the known cool subcluster, a new structure was resolved 2
east of the peak of the main cluster. Its position is roughtly at the center of
a low-brightness radio halo. Spectral analysis shows that the "shoulder" has
high iron abundance ( 1). We suggest that this structure is either
another merging component or an internal structure of the main cluster. The
X-ray redshifts of several regions were measured. The results agree with the
optical ones and suggest that the main cluster, the subcluster and the
"shoulder" are physically associated and interacting. The subcluster has low
temperature ( 4.5 keV) and high iron abundance ( 0.6) in the
central 150 kpc. The \chandra image shows a relatively sharp brightness
gradient at the south of the subcluster peak running south-south-east (SSE). A
temperature jump was found across the edge, with higher temperature ahead of
the edge in the low density region. This phenomenon is qualitatively similar to
the "cold fronts" found in A2142 and A3667. If the "shoulder" is ignored, the
temperature map resembles those simulations at the early stage of merging while
the subcluster approached the main cluster from somewhere west. This fact and
the observed edge, in combination with the clear iron abundance contrast
between the center of the subcluster ( 0.6) and the main cluster (
0.2), all imply that the ongoing merger is still at the early stage. At least
three member galaxies, including a radio head-tail galaxy, were found to have
corresponding X-ray emission.Comment: The revised version. The shown abstract is shrunk. Accepted by ApJ.
If it is possible, please try to look at the high-resolution version is
http://cfa160.harvard.edu/~sunm/a2256.tar.g
Chandra View of the Dynamically Young Cluster of Galaxies A1367 I. Small-Scale Structures
The 40 ks \emph{Chandra} ACIS-S observation of A1367 provides new insights
into small-scale structures and point sources in this dynamically young
cluster. Here we concentrate on small-scale extended structures. A ridge-like
structure around the center (``the ridge'') is significant in the \chandra\
image. The ridge, with a projected length of 8 arcmin (or 300
h kpc), is elongated from northwest (NW) to southeast (SE), as is
the X-ray surface brightness distribution on much larger scales ( 2
h Mpc). The ridge is cooler than its western and southern
surroundings while the differences from its eastern and northern surroundings
are small. We also searched for small-scale structures with sizes
arcmin. Nine extended features, with sizes from 0.5 to 1.5, were
detected at significance levels above 4 . Five of the nine features are
located in the ridge and form local crests. The nine extended features can be
divided into two types. Those associated with galaxies (NGC 3860B, NGC 3860 and
UGC 6697) are significantly cooler than their surroundings (0.3 - 0.9 keV vs. 3
- 4.5 keV). The masses of their host galaxies are sufficient to bind the
extended gas. These extended features are probably related to thermal halos or
galactic superwinds of their host galaxies. The existence of these relatively
cold halos imply that galaxy coronae can survive in cluster environment (e.g.,
Vikhlinin et al. 2001). Features of the second type are not apparently
associated with galaxies. Their temperatures may not be significantly different
from those of their surroundings. This class of extended features may be
related to the ridge. We consider several possibilities for the ridge and the
second type of extended features. The merging scenario is preferred.Comment: To appear in ApJ, Vol 576, 2002, Sep., a high-resolution version is
in http://cfa160.harvard.edu/~sunm/a1367_a.ps.g
Observing H2 Emission in Forming Galaxies
We study the H2 cooling emission of forming galaxies, and discuss their
observability using the future infrared facility SAFIR. Forming galaxies with
mass >10^11 Msun emit most of their gravitational energy liberated by
contraction in molecular hydrogen line radiation, although a large part of
thermal energy at virialization is radiated away by the H Ly alpha emission.
For more massive objects, the degree of heating due to dissipation of kinetic
energy is so great that the temperature does not drop below 10^4 K and the
gravitational energy is emitted mainly by the Ly alpha emission. Therefore, the
total H2 luminosity attains the peak value of about 10^42 ergs/s for forming
galaxies whose total mass 10^11 Msun. If these sources are situated at redshift
z=8, they can be detected by rotational lines of 0-0S(3) at 9.7 micron and
0-0S(1) at 17 micron by SAFIR. An efficient way to find such H2 emitters is to
look at the Ly alpha emitters, since the brightest H2 emitters are also
luminous in the Ly alpha emission.Comment: 20 pages, 7 figures, ApJ accepte
Nonlinear stochastic biasing from the formation epoch distribution of dark halos
We propose a physical model for nonlinear stochastic biasing of one-point
statistics resulting from the formation epoch distribution of dark halos. In
contrast to previous works on the basis of extensive numerical simulations, our
model provides for the first time an analytic expression for the joint
probability function. Specifically we derive the joint probability function of
halo and mass density contrasts from the extended Press-Schechter theory. Since
this function is derived in the framework of the standard gravitational
instability theory assuming the random-Gaussianity of the primordial density
field alone, we expect that the basic features of the nonlinear and stochastic
biasing predicted from our model are fairly generic. As representative
examples, we compute the various biasing parameters in cold dark matter models
as a function of a redshift and a smoothing length. Our major findings are (1)
the biasing of the variance evolves strongly as redshift while its
scale-dependence is generally weak and a simple linear biasing model provides a
reasonable approximation roughly at R\simgt 2(1+z)\himpc, and (2) the
stochasticity exhibits moderate scale-dependence especially on R\simlt
20\himpc, but is almost independent of . Comparison with the previous
numerical simulations shows good agreement with the above behavior, indicating
that the nonlinear and stochastic nature of the halo biasing is essentially
understood by taking account of the distribution of the halo mass and the
formation epoch.Comment: 34 pages, 11 figures, ApJ (2000) in pres
Submillimeter detection of the Sunyaev -- Zel'dovich effect toward the most luminous X-ray cluster at z=0.45
We report on the detection of the Sunyaev -- Zel'dovich (SZ) signals toward
the most luminous X-ray cluster RXJ1347-1145 at Nobeyama Radio Observatory (21
and 43 GHz) and at James Clerk Maxwell Telescope (350 GHz). In particular the
latter is the first successful detection of the SZ temperature increment in the
submillimeter band which resolved the profile of a cluster of galaxies. Both
the observed spectral dependence and the radial profile of the SZ signals are
fully consistent with those expected from the X-ray observation of the cluster.
The combined analysis of 21GHz and 350GHz data reproduces the temperature and
core-radius of the cluster determined with the ROSAT and ASCA satellites when
we adopt the slope of the density profile from the X-ray observations.
Therefore our present data provide the strongest and most convincing case for
the detection of the submillimeter SZ signal from the cluster, as well as in
the Rayleigh -- Jeans regime. We also discuss briefly the cosmological
implications of the present results.Comment: 11 pages, The Astrophysical Journal (Letters), in pres
- …