245 research outputs found
Narrow Band X-ray Photometry as a Tool for Studying Galaxy and Cluster Mass Distributions
We explore the utility of narrow band X-ray surface photometry as a tool for
making fully Bayesian, hydrostatic mass measurements of clusters of galaxies,
groups and early-type galaxies. We demonstrate that it is sufficient to measure
the surface photometry with the Chandra X-ray observatory in only three (rest
frame) bands (0.5--0.9 keV, 0.9--2.0 keV and 2.0--7.0 keV) in order to
constrain the temperature, density and abundance of the hot interstellar medium
(ISM). Adopting parametrized models for the mass distribution and radial
entropy profile and assuming spherical symmetry, we show that the constraints
on the mass and thermodynamic properties of the ISM that are obtained by
fitting data from all three bands simultaneously are comparable to those
obtained by fitting similar models to the temperature and density profiles
derived from spatially resolved spectroscopy, as is typically done. We
demonstrate that the constraints can be significantly tightened when exploiting
a recently derived, empirical relationship between the gas fraction and the
entropy profile at large scales, eliminating arbitrary extrapolations at large
radii. This "Scaled Adiabatic Model" (ScAM) is well suited to modest
signal-to-noise data, and we show that accurate, precise measurements of the
global system properties are inferred when employing it to fit data from even
very shallow, snapshot X-ray observations. The well-defined asymptotic
behaviour of the model also makes it ideally suited for use in
Sunyaev-Zeldovich studies of galaxy clusters.Comment: 15 pages, 6 figures. Accepted for Publication in MNRA
Bolted Timber Connections: Part II. Bolt Bending and Associated Wood Deformation
Complete double-shear joints with a single bolt were tested in tension. Approximately 10 X-ray scans were made of each joint as it was progressively loaded to failure; in this way, bending and overall displacement of the bolts within the members could be quantified. Combining the above data with measured joint-slip values enables the penetration of the bolt into the surrounding wood to be calculated for all positions along the length of the bolt. In a preceding related study, the authors observed the mechanisms of deformation that occur in thin wood wafers around a round steel pin of a diameter identical to that of the bolts used in the present work. By combining this information on behavior mechanisms in the plane at right angles to the pin axis with the X-ray data for whole joints, wood behavior throughout the joint and reactions against the bolt along its length can be estimated. The above analysis is applied principally to joints with 75- x 75-mm wood main members, 75- x 37.5-mm wood side members, and a single 12.5-mm diameter bolt an an end-distance of seven diameters. Representative X-ray scans of joints manufactured with a range of steel side-member thicknesses and bolt diameters are also included. The techniques presented complement theoretical model predictions and thus may be used to aid in optimizing joint design
Bolted Timber Connections. Part I. a Wafer Technique to Model Wood Deformation Around Bolts
An experimental technique to model wood material behavior in the plane perpendicular to the axes of bolts in joint members is described. In this technique, 0.8-mm-thick wood wafers sandwiched between glass plates, with a steel pin representing a bolt passing through them, are loaded in tension. Wood deformation and failure around the pin, visible through the glass plates as loading proceeds, are photographed, and load-slip curves are also recorded. Reported tests were limited to steel pins of 12.5-mm diameter; preliminary findings suggest that information can be gained that sheds light on the effects of growth-ring orientation, wood defects, bolt end-distance, and multiple-bolt positions. The technique may be used directly, to indicate the sensitivity of joints to design factors such as those above, or indirectly, when results are combined with bolt bending data obtained with X-ray scanning
Low-Mass X-ray Binaries and Globular Clusters in Early-Type Galaxies. I. Chandra Observations
We present a Chandra survey of LMXBs in 24 early-type galaxies. Correcting
for detection incompleteness, the X-ray luminosity function (XLF) of each
galaxy is consistent with a powerlaw with negative logarithmic differential
slope, beta~2.0. However, beta strongly correlates with incompleteness,
indicating the XLF flattens at low-Lx. The composite XLF is well-fitted by a
powerlaw with a break at 2.21(+0.65,-0.56)E38 erg/s and beta=1.40(+0.10,-0.13)
and 2.84(+0.39,-0.30) below and above it, respectively. The break is close to
the Eddington limit for a 1.4Msun neutron-star, but the XLF shape rules out its
representing the division between neutron-star and black-hole systems. Although
the XLFs are similar, we find evidence of some variation between galaxies. The
high-Lx XLF slope does not correlate with age, but may correlate with
[alpha/Fe]. Considering only LMXBs with Lx>1E37 erg/s, matching the LMXBs with
globular clusters (GCs) identified in HST observations of 19 of the galaxies,
we find the probability a GC hosts an LMXB is proportional to LGC^alpha
ZFe^gamma} where alpha=1.01+/-0.19 and gamma=0.33+/-0.11. Correcting for GC
luminosity and colour effects, and detection incompleteness, we find no
evidence that the fraction of LMXBs with Lx>1e37 erg/s in GCs (40%), or the
fraction of GCs hosting LMXBs (~6.5%) varies between galaxies. The spatial
distribution of LMXBs resembles that of GCs, and the specific frequency of
LMXBs is proportional to the GC specific luminosity, consistent with the
hypothesis that all LMXBs form in GCs. If the LMXB lifetime is tau and the duty
cycle is Fd, our results imply ~1.5 (tau/1E8 yr)^-1 /Fd LMXBs are formed per
Gyr per GC and we place an upper limit of 1 active LMXB in the field per
3.4E9Lsun of V-band luminosity.Comment: 24 pages, 17 figures and 6 tables. Accepted for publication in the
Astrophysical Journal. Expanded discussion and various minor revisions to
improve robustness of results. Conclusions unchange
Sterile neutrino dark matter bounds from galaxies of the Local Group
We show that the canonical oscillation-based (non-resonant) production of
sterile neutrino dark matter is inconsistent at % confidence with
observations of galaxies in the Local Group. We set lower limits on the
non-resonant sterile neutrino mass of keV (equivalent to keV
thermal mass) using phase-space densities derived for dwarf satellite galaxies
of the Milky Way, as well as limits of keV (equivalent to keV
thermal mass) based on subhalo counts of -body simulations of M 31
analogues. Combined with improved upper mass limits derived from significantly
deeper X-ray data of M 31 with full consideration for background variations, we
show that there remains little room for non-resonant production if sterile
neutrinos are to explain % of the dark matter abundance. Resonant and
non-oscillation sterile neutrino production remain viable mechanisms for
generating sufficient dark matter sterile neutrinos.Comment: 10 pages, 4 figures, 2 tables. Submitted to PR
The ELIXR Galaxy Survey. II: Baryons and Dark Matter in an Isolated Elliptical Galaxy
The Elliptical Isolated X-ray (ElIXr) Galaxy Survey is a volume-limited
(<110Mpc) study of optically selected, isolated, Lstar elliptical galaxies, to
provide an X-ray census of galaxy-scale (virial mass, Mvir < 1e13 Msun)
objects, and identify candidates for detailed hydrostatic mass modelling. In
this paper, we present a Chandra and XMM study of one such candidate, NGC1521,
and constrain its distribution of dark and baryonic matter. We find a
morphologically relaxed hot gas halo, extending almost to R500, that is well
described by hydrostatic models similar to the benchmark, baryonically closed,
Milky Way-mass elliptical galaxy NGC720. We obtain good constraints on the
enclosed gravitating mass (M500=3.8e12+/-1e12 Msun, slightly higher than
NGC\thin 720), and baryon fraction (fb500=0.13+/-0.03). We confirm at 8.2-sigma
the presence of a dark matter (DM) halo consistent with LCDM. Assuming a
Navarro-Frenk-White DM profile, our self-consistent, physical model enables
meaningful constraints beyond R500, revealing that most of the baryons are in
the hot gas. Within the virial radius, fb is consistent with the Cosmic mean,
suggesting that the predicted massive, quasi-hydrostatic gas halos may be more
common than previously thought. We confirm that the DM and stars conspire to
produce an approximately powerlaw total mass profile (rho \propto r^-alpha)
that follows the recently discovered scaling relation between alpha and optical
effective radius. Our conclusions are insensitive to modest, observationally
motivated, deviations from hydrostatic equilibrium. Finally, after correcting
for the enclosed gas fraction, the entropy profile is close to the self-similar
prediction of gravitational structure formation simulations, as observed in
massive galaxy clusters.Comment: Accepted for publication in the Astrophysical Journal. Minor
modifications to match accepted version. Conclusions unchanged. 18 pages, 11
figures and 3 table
A Chandra view of the normal S0 galaxy NGC 1332: I. An unbroken, steep power law luminosity function for the LMXB population
Chandra ACIS-S3 observations of the S0 galaxy NGC 1332 resolve much of the
emission into 73 point-sources, of which 37 lie within the D_25 isophote. The
unresolved emission is discussed in two companion papers. The source luminosity
function (XLF) shows the break seen in other early-type galaxies at
\~2x10^{38}ergs/s. After correcting for detection incompleteness due to source
confusion and contamination from diffuse emission, the break vanishes and the
data are well-described as a single power law. This casts further doubt on
there being a ``universal'' XLF break in such galaxies dividing neutron-star
and black-hole systems. The slope of the differential XLF (dN/dL),
beta=2.7+/-0.5, is marginally (~2.5 sigma) steeper than has been found for
analogous fits of other early-type galaxies but resembles what is generally
seen at high luminosities. Two of the sources within D_25 are ULX, although
neither have L_X>2x 10^{39} ergs/s. The absence of very luminous ULX in
early-type galaxies suggests a break in the XLF slope at ~1-2x 10^{39} ergs/s,
but we cannot constrain it in NGC 1332. The sources have a spatial distribution
consistent with the optical light and display a range of properties expected
for a LMXB population. The spectra of the individual sources, as well as the
composite source spectra, agree with observations of other early-type galaxies,
although a small number of highly-absorbed sources are seen. Two sources have
very soft spectra, two show strong variability and one source shows evidence of
an extended radial profile. We do not detect a central source in NGC 1332, but
we find a faint (L_X=2+/-1 x 10^{38} ergs/s) point-source coincident with the
centre of the companion dwarf galaxy NGC 1331. (Abridged)Comment: 14 pages, 8 figures. Accepted for publication in ApJ. Minor changes
to match published versio
A Chandra View of the Normal SO Galaxy NGC 1332: II: Solar Abundances in the Hot Gas and Implications for SN Enrichment
We present spectral analysis of the diffuse emission in the normal, isolated,
moderate-Lx S0 NGC 1332, constraining both the temperature profile and the
metal abundances in the ISM. The characteristics of the point source population
and the gravitating matter are discussed in two companion papers. The diffuse
emission comprises hot gas, with an ~isothermal temperature profile (~0.5 keV),
and emission from unresolved point-sources. In contrast with the cool cores of
many groups and clusters, we find a small central temperature peak. We obtain
emission-weighted abundance contraints within 20 kpc for several key elements:
Fe, O, Ne, Mg and Si. The measured iron abundance (Z_Fe=1.1 in solar units;
>0.53 at 99% confidence) strongly excludes the very sub-solar values often
historically reported for early-type galaxies but agrees with recent
observations of brighter galaxies and groups. The abundance ratios, with
respect to Fe, of the other elements were also found to be ~solar, although
Z_o/Z_Fe was significantly lower (<0.4). Such a low O abundance is not
predicted by simple models of ISM enrichment by Type Ia and Type II supernovae,
and may indicate a significant contribution from primordial hypernovae.
Revisiting Chandra observations of the moderate-Lx, isolated elliptical NGC
720, we obtain similar abundance constraints. Adopting standard SNIa and SNII
metal yields, our abundance ratio constraints imply 73+/-5% and 85+/-6% of the
Fe enrichment in NGC 1332 and NGC 720, respectively, arises from SNIa. Although
these results are sensitive to the considerable systematic uncertainty in the
SNe yields, they are in good agreement with observations of more massive
systems. These two moderate-Lx early-type galaxies reveal a consistent pattern
of metal enrichment from cluster scales to moderate Lx/Lb galaxies. (abridged)Comment: 12 pages, 4 figures, accepted for publication in ApJ. Minor changes
to match published versio
X-Ray Absorption By WHIM in the Sculptor Wall
We present XMM RGS and Chandra LETG observations of the blazar, H 2356-309,
located behind the Sculptor Wall, a large-scale galaxy structure expected to
harbor high-density Warm-Hot Intergalactic Medium (WHIM). Our simultaneous
analysis of the RGS and LETG spectra yields a 3-sigma detection of the crucial
redshifted O vii K-alpha line with a column density (>~ 10^{16} cm^{-2})
consistent with similar large-scale structures produced in cosmological
simulations. This represents the first detection of non-local WHIM from X-ray
absorption studies where XMM and Chandra data are analyzed simultaneously and
the absorber redshift is already known, thus providing robust evidence for the
expected repository of the "missing baryons".Comment: Accepted for Publication in The Astrophysical Journal, 7 pages, 2
figure
- …