2,170 research outputs found
Intrinsic scatter of caustic masses and hydrostatic bias: An observational study
All estimates of cluster mass have some intrinsic scatter and perhaps some
bias with true mass even in the absence of measurement errors for example
caused by cluster triaxiality and large scale structure. Knowledge of the bias
and scatter values is fundamental for both cluster cosmology and astrophysics.
In this paper we show that the intrinsic scatter of a mass proxy can be
constrained by measurements of the gas fraction because masses with higher
values of intrinsic scatter with true mass produce more scattered gas
fractions. Moreover, the relative bias of two mass estimates can be constrained
by comparing the mean gas fraction at the same (nominal) cluster mass. Our
observational study addresses the scatter between caustic (i.e., dynamically
estimated) and true masses, and the relative bias of caustic and hydrostatic
masses. For these purposes, we used the X-ray Unbiased Cluster Sample, a
cluster sample selected independently from the intracluster medium content with
reliable masses: 34 galaxy clusters in the nearby () Universe,
mostly with , and with caustic masses.
We found a 35\% scatter between caustic and true masses. Furthermore, we found
that the relative bias between caustic and hydrostatic masses is small,
dex, improving upon past measurements. The small scatter found
confirms our previous measurements of a highly variable amount of feedback from
cluster to cluster, which is the cause of the observed large variety of
core-excised X-ray luminosities and gas masses.Comment: A&A, in press, minor language changes from previous versio
Diffuse Gas and LMXBs in the Chandra Observation of the S0 Galaxy NGC 1553
We have spatially and spectrally resolved the sources of X-ray emission from
the X-ray faint S0 galaxy NGC 1553 using an observation from the Chandra X-ray
Observatory. The majority (70%) of the emission in the 0.3 - 10.0 keV band is
diffuse, and the remaining 30% is resolved into 49 discrete sources. Most of
the discrete sources associated with the galaxy appear to be low mass X-ray
binaries (LMXBs). The luminosity function of the LMXB sources is well-fit by a
broken power-law with a break luminosity comparable to the Eddington luminosity
for a 1.4 solar mass neutron star. It is likely that those sources with
luminosities above the break are accreting black holes and those below are
mostly neutron stars in binary systems. Spectra were extracted for the total
emission, diffuse emission, and sum of the resolved sources; the spectral fits
for all require a model including both a soft and hard component. The diffuse
emission is predominately soft while the emission from the sources is mostly
hard. Approximately 24% of the diffuse emission arises from unresolved LMXBs,
with the remainder resulting from thermal emission from hot gas. There is a
very bright source at the projected position of the nucleus of the galaxy. The
spectrum and luminosity derived from this central source are consistent with it
being an AGN; the galaxy also is a weak radio source. Finally, the diffuse
emission exhibits significant substructure with an intriguing spiral feature
passing through the center of the galaxy. The X-ray spectrum and surface
brightness of the spiral feature are consistent with adiabatic or shock
compression of ambient gas, but not with cooling. This feature may be due to
compression of the hot interstellar gas by radio lobes or jets associated with
the AGN.Comment: 23 pages using emulateapj.sty; ApJ, in press; revised version
includes correction to error in the L_X,src/L_B ratio as well as other
revision
Origin of the scatter in the X-ray luminosity of early-type galaxies observed with ROSAT
Statistical properties of X-ray luminosity and temperature are studied for 52
early-type galaxies based on the ROSAT PSPC data. All of the X-ray luminous
galaxies show largely extended emission with a radius of a few times of
10, while X-ray faint galaxies do not show such a component. This leads to
a division of early-type galaxies into two categories: X-ray extended and X-ray
compact galaxies. Except for a few galaxies in dense cluster environments, the
luminosity and temperature of X-ray compact galaxies are well explained by a
kinematical heating of the gas supplied by stellar mass loss. In contrast,
X-ray extended galaxies indicate large scatter in the X-ray luminosity. We
discuss that X-ray extended galaxies are the central objects of large potential
structures, and the presence and absence of this potential is the main origin
of the large scatter in the X-ray luminosity.Comment: 35 pages, including 8 figures, Accepted for publication in Ap
Relative Sizes of X-ray and Optical Images of Elliptical Galaxies; Correlation with X-ray Luminosity
Optical parameters of elliptical galaxies are tightly correlated, but their
x-ray parameters vary widely. The x-ray luminosity L_x ranges over more than an
order of magnitude for ellipticals having similar optical luminosity L_B. The
source of this scatter has been elusive. We show here that the dispersion in
L_x for fixed optical luminosity L_B correlates strongly with the dimensionless
ratio of the sizes of the x-ray and optical images, r_ex/r_e. Specifically, we
find that (L_x/L_B) is proportional to (r_{ex}/r_e)^{0.60 \pm 0.30}, a version
of the correlation that is independent of distance. This correlation may be a
natural result of mergings and tidal truncations that are expected during the
formation and early evolution of ellipticals in groups of galaxies. The radial
structure of x-ray images also varies: some are compact (e.g. NGC 4649, 7626,
5044), others diffuse (e.g. NGC 4636, 1399).Comment: 5 pages, 3 figures. Accepted for publication in Astrophysical Journal
Letter
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