581 research outputs found
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
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
A Census of Baryons and Dark Matter in an Isolated, Milky Way-sized Elliptical Galaxy
We present a study of the dark and luminous matter in the isolated elliptical
galaxy NGC720, based on deep X-ray observations made with Chandra and Suzaku.
The gas is reliably measured to ~R2500, allowing us to place good constraints
on the enclosed mass and baryon fraction (fb) within this radius
(M2500=1.6e12+/-0.2e12 Msun, fb(2500)=0.10+/-0.01; systematic errors are
<~20%). The data indicate that the hot gas is close to hydrostatic, which is
supported by good agreement with a kinematical analysis of the dwarf satellite
galaxies. We confirm a dark matter (DM) halo at ~20-sigma. Assuming an NFW DM
profile, our physical model for the gas distribution enables us to obtain
meaningful constraints at scales larger than R2500, revealing that most of the
baryons are in the hot gas. We find that fb within Rvir is consistent with the
Cosmological value, confirming theoretical predictions that a ~Milky Way-mass
(Mvir=3.1e12+/-0.4e12 Msun) galaxy can sustain a massive, quasi-hydrostatic gas
halo. While fb is higher than the cold baryon fraction typically measured in
similar-mass spiral galaxies, both the gas fraction (fg) and fb in NGC720 are
consistent with an extrapolation of the trends with mass seen in massive galaxy
groups and clusters. After correcting for fg, the entropy profile is close to
the self-similar prediction of gravitational structure formation simulations,
as observed in galaxy clusters. Finally, we find a strong heavy metal abundance
gradient in the ISM similar to those observed in massive galaxy groups.Comment: 23 pages, 13 figures, 4 tables. Accepted for publication in the
Astrophysical Journal. Minor modifications to match accepted version.
Conclusions unchange
X-ray Isophotes in a Rapidly Rotating Elliptical Galaxy: Evidence of Inflowing Gas
We describe two-dimensional gasdynamical computations of the X-ray emitting
gas in the rotating elliptical galaxy NGC 4649 that indicate an inflow of about
one solar mass per year at every radius. Such a large instantaneous inflow
cannot have persisted over a Hubble time. The central constant-entropy
temperature peak recently observed in the innermost 150 parsecs is explained by
compressive heating as gas flows toward the central massive black hole. Since
the cooling time of this gas is only a few million years, NGC 4649 provides the
most acutely concentrated known example of the cooling flow problem in which
the time-integrated apparent mass that has flowed into the galactic core
exceeds the total mass observed there. This paradox can be resolved by
intermittent outflows of energy or mass driven by accretion energy released
near the black hole. Inflowing gas is also required at intermediate kpc radii
to explain the ellipticity of X-ray isophotes due to spin-up by mass ejected by
stars that rotate with the galaxy and to explain local density and temperature
profiles. We provide evidence that many luminous elliptical galaxies undergo
similar inflow spin-up. A small turbulent viscosity is required in NGC 4649 to
avoid forming large X-ray luminous disks that are not observed, but the
turbulent pressure is small and does not interfere with mass determinations
that assume hydrostatic equilibrium.Comment: 21 pages, 9 figures, accepted for publication by Ap
Detection of A Transient X-ray Absorption Line Intrinsic to the BL Lacertae Object H 2356-309
Since the launch of the Einstein X-ray Observatory in the 1970s, a number of
broad absorption features have been reported in the X-ray spectra of BL Lac
objects. These features are often interpreted as arising from high velocity
outflows intrinsic to the BL Lac object, therefore providing important
information about the inner environment around the central engine. However,
such absorption features have not been observed more recently with
high-resolution X-ray telescopes such as Chandra and XMM-Newton. In this paper,
we report the detection of a transient X-ray absorption feature intrinsic to
the BL Lac object H 2356-309 with the Chandra X-ray Telescope. This BL Lac
object was observed during XMM cycle 7, Chandra cycle 8 and 10, as part of our
campaign to investigate X-ray absorption produced by the warm-hot intergalactic
medium (WHIM) residing in the foreground large scale superstructure. During one
of the 80 ksec, Chandra cycle 10 observations, a transient absorption feature
was detected at 3.3-sigma (or 99.9% confidence level, accounting for the number
of trials), which we identify as the OVIII K-alpha line produced by an absorber
intrinsic to the BL Lac object. None of the other 11 observations showed this
line. We constrain the ionization parameter (25 <~ Xi <~ 40) and temperature
(10^5 < T < 2.5 10^7 K) of the absorber. This absorber is likely produced by an
outflow with a velocity up to 1,500 km/s. There is a suggestion of possible
excess emission on the long-wavelength side of the absorption line; however,
the derived properties of the emission material are very different from those
of the absorption material, implying it is unlikely a typical P Cygni-type
profile.Comment: 7 pages, 4 figures, accepted for publication in Ap
Studying the WHIM Content of the Galaxy Large-Scale Structures along the Line of Sight to H 2356-309
We make use of a 500ks Chandra HRC-S/LETG spectrum of the blazar H2356-309,
combined with a lower S/N spectrum of the same target, to search for the
presence of warm-hot absorbing gas associated with two Large-Scale Structures
(LSSs) crossed by this sightline at z=0.062 (the Pisces-Cetus Supercluster,
PCS) and at z=0.128 ("Farther Sculptor Wall", FSW). No statistically
significant (>=3sigma) individual absorption is detected from any of the strong
He- or H-like transitions of C, O and Ne at the redshifts of the structures.
However we are still able to constrain the physical and geometrical parameters
of the associated putative absorbing gas, by performing joint spectral fit of
marginal detections and upper limits of the strongest expected lines with our
self-consistent hybrid ionization WHIM spectral model. At the redshift of the
PCS we identify a warm phase with logT=5.35_-0.13^+0.07 K and log N_H
=19.1+/-0.2 cm^-2 possibly coexisting with a hotter and less significant phase
with logT=6.9^+0.1_-0.8 K and log N_H=20.1^+0.3_-1.7 cm^-2 (1sigma errors). For
the FSW we estimate logT=6.6_-0.2^+0.1 K and log N_H=19.8_-0.8^+0.4 cm^-2. Our
constraints allow us to estimate the cumulative number density per unit
redshifts of OVII WHIM absorbers. We also estimate the cosmological mass
density obtaining Omega_b(WHIM)=(0.021^+0.031_-0.018) (Z/Z_sun)^-1, consistent
with the mass density of the intergalactic 'missing baryons' for high
metallicities.Comment: 29 pages, 8 figures, 4 tables. Accepted for publication in Ap
Rotation and Turbulence of the Hot ICM in Galaxy Clusters
Cosmological simulations of galaxy clusters typically find that the weight of
a cluster at a given radius is not balanced entirely by the thermal gas
pressure of the hot ICM, with theoretical studies emphasizing the role of
random turbulent motions to provide the necessary additional pressure support.
Using a set of high-resolution, hydrodynamical simulations of galaxy clusters
that include radiative cooling and star formation, we find instead that in the
most relaxed clusters rotational support exceeds that from random turbulent
motions for radii 0.1 - 0.5 r_500, and that the observed clusters are much
rounder than the simulated, relaxed clusters within ~ 0.4 r_500. Moreover,
while the observed clusters display an average ellipticity profile that does
not vary significantly with radius, the ellipticity of the relaxed CDM clusters
declines markedly with increasing radius, suggesting that the ICM of the
observed clusters rotates less rapidly than that of the relaxed CDM clusters
out to ~ 0.6 r_500. We also find the ellipticity profile of a simulated cluster
without radiative cooling is in much better agreement with the observations,
implying that over-cooling has a substantial impact on the gas dynamics and
morphology out to larger radii than previously recognized. It also suggests
that the 10%-20% systematic errors from non-thermal gas pressure support
reported for simulated cluster masses, obtained from fitting simulated X-ray
data over large radial ranges within r_500, may need to be revised downward.
These results demonstrate the utility of X-ray ellipticity profiles as a probe
of ICM rotation and over-cooling which should be used to constrain future
cosmological cluster simulations.Comment: 13 pages, 8 figures, accepted for publication in Ap
Facile hydrothermal synthesis and optical limiting properties of TiO 2 -reduced graphene oxide nanocomposites
TiO2/reduced graphene oxide (RGO) nanocomposites Gx (RGO titania nanocomposite, x grams tetrabutyl titanate per 0.03 g RGO, x = 0.25, 0.50, 1.00) were prepared by a hydrothermal method: graphene oxide was reduced to RGO in a 2:1 water:ethanol mixture in the presence of varying quantities of tetrabutyl titanate, which deposited as TiO2 on the RGO sheets. The nanocomposites were characterized by a combination of Fourier transform infrared spectroscopy, diffuse reflectance ultraviolet-visible spectroscopy, photoluminescence spectroscopy, Raman spectroscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy studies. The nanocomposite G0.25 exhibits enhanced nonlinear optical properties compared to its individual components, which is ascribed to a combination of mechanisms. The role of defects and electron/energy transfer in the optical limiting performance of G0.25 was clarified with the help of Raman and photoluminescence spectroscopies. Intensity-dependent switching between reverse saturable absorption and saturable absorption behavior was observed with the G0.50 nanocomposite
Adaptive GPU-accelerated force calculation for interactive rigid molecular docking using haptics
Molecular docking systems model and simulate in silico the interactions of intermolecular binding. Haptics-assisted docking enables the user to interact with the simulation via their sense of touch but a stringent time constraint on the computation of forces is imposed due to the sensitivity of the human haptic system. To simulate high fidelity smooth and stable feedback the haptic feedback loop should run at rates of 500 Hz to 1 kHz. We present an adaptive force calculation approach that can be executed in parallel on a wide range of Graphics Processing Units (GPUs) for interactive haptics-assisted docking with wider applicability to molecular simulations. Prior to the interactive session either a regular grid or an octree is selected according to the available GPU memory to determine the set of interatomic interactions within a cutoff distance. The total force is then calculated from this set. The approach can achieve force updates in less than 2 ms for molecular structures comprising hundreds of thousands of atoms each, with performance improvements of up to 90 times the speed of current CPU-based force calculation approaches used in interactive docking. Furthermore, it overcomes several computational limitations of previous approaches such as pre-computed force grids, and could potentially be used to model receptor flexibility at haptic refresh rates
Self-Assembling Peptide Detergents Stabilize Isolated Photosystem Ion a Dry Surface for an Extended Time
We used a class of designed peptide detergents to stabilize photosystem I (PS-I) upon extended drying under N(2) on a gold-coated-Ni-NTA glass surface. PS-I is a chlorophyll-containing membrane protein complex that is the primary reducer of ferredoxin and the electron acceptor of plastocyanin. We isolated the complex from the thylakoids of spinach chloroplasts using a chemical detergent. The chlorophyll molecules associated with the PS-I complex provide an intrinsic steady-state emission spectrum between 650 and 800 nm at −196.15 °C that reflects the organization of the pigment-protein interactions. In the absence of detergents, a large blue shift of the fluorescence maxima from approximately 735 nm to approximately 685 nm indicates a disruption in light-harvesting subunit organization, thus revealing chlorophyll−protein interactions. The commonly used membrane protein-stabilizing detergents, N-dodecyl-β-D-maltoside and N-octyl-β-D-glucoside, only partially stabilized the approximately 735-nm complex with approximately 685-nm spectroscopic shift. However, prior to drying, addition of the peptide detergent acetyl- AAAAAAK at increasing concentration significantly stabilized the PS-I complex. Moreover, in the presence of acetyl- AAAAAAK, the PS-I complex is stable in a dried form at room temperature for at least 3 wk. Another peptide detergent, acetyl-VVVVVVD, also stabilized the complex but to a lesser extent. These observations suggest that the peptide detergents may effectively stabilize membrane proteins in the solid-state. These designed peptide detergents may facilitate the study of diverse types of membrane proteins
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