942 research outputs found
The Dark Matter Radial Profile in the Core of the Relaxed Cluster A2589
We present an analysis of a Chandra--ACIS observation of the galaxy cluster
A2589 to constrain the radial distribution of the total gravitating matter and
the dark matter in the core of the cluster. A2589 is especially well-suited for
this analysis because the hot gas in its core region (r < ~0.1 Rvir) is
undisturbed by interactions with a central radio source. From the largest
radius probed (r=0.07 Rvir) down to r ~0.02 Rvir dark matter dominates the
gravitating mass. Over this region the radial profiles of the gravitating and
dark matter are fitted well by the NFW and Hernquist profiles predicted by CDM.
The density profiles are also described well by power laws, rho ~r^{-alpha},
where alpha=1.37 +/- 0.14 for the gravitating matter and alpha=1.35 +/- 0.21
for the dark matter. These values are consistent with profiles of CDM halos but
are significantly larger than alpha ~0.5 found in LSB galaxies and expected
from self-interacting dark matter models.Comment: 10 pages, 6 figures, To Appear in The Astrophysical Journal, March 20
issue, a few very minor changes to match copyedited versio
New X-ray Clusters in the EMSS II: Optical Properties
We present optical images for 9 new clusters of galaxies we have found in a
reanalysis of the Einstein IPC images comprising the Extended Medium
Sensitivity Survey (EMSS). Based on the presence of a red sequence of galaxies
in a color-magnitude (CM) diagram, a redshift is estimated for each cluster.
Galaxy overdensities (cluster richnesses) are measured in each field using the
B_gc statistic which allows their plausible identification with the X-ray
emission. The nature of our X-ray detection algorithm suggests that most of
these clusters have low X-ray surface brightness (LSB) compared to the
previously known EMSS clusters. We compare the optical and X-ray observations
of these clusters with the well-studied Canadian Network for Observational
Cosmology (CNOC) subsample of the EMSS, and conclude that the new clusters
exhibit a similar range of optical richnesses, X-ray luminosities, and,
somewhat surprisingly, galaxy populations as the predominantly rich, relaxed
EMSS/CNOC clusters.Comment: Accepted to ApJ, 17 pages, 14 figures, uses emulateapj5.st
WASP-39b: exo-Saturn with patchy cloud composition, moderate metallicity, and underdepleted S/O
WASP-39b is one of the first extrasolar giant gas planets that has been
observed within the JWST ERS program. Fundamental properties that may enable
the link to exoplanet formation differ amongst retrieval methods, for example
metallicity and mineral ratios.
In this work, the formation of clouds in the atmosphere of WASP-39b is
explored to investigate how inhomogeneous cloud properties (particle sizes,
material composition, opacity) may be for this intermediately warm gaseous
exoplanet. WASP-39b's atmosphere has a comparable day-night temperature median
with sufficiently low temperatures that clouds may form globally. The presence
of clouds on WASP-39b can explain observations without resorting to a high (>
100x solar) metallicity atmosphere for a reduced vertical mixing efficiency.
The assessment of mineral ratios shows an under-depletion of S/O due to
condensation compared to C/O, Mg/O, Si/O, Fe/O ratios. Vertical patchiness due
to heterogeneous cloud composition challenges simple cloud models. An equal
mixture of silicates and metal oxides is expected to characterise the cloud
top. Further, optical properties of Fe and Mg silicates in the mid-infrared
differ significantly which will impact the interpretation of JWST observations.
We conclude that WASP-39b's atmosphere contains clouds and the underdepletion
of S/O by atmospheric condensation processes suggest the use of sulphur gas
species as a possible link to primordial element abundances. Over-simplified
cloud models do not capture the complex nature of mixed-condensate clouds in
exoplanet atmospheres. The clouds in the observable upper atmosphere of
WASP-39b are a mixture of different silicates and metal oxides. The use of
constant particles sizes and/or one-material cloud particles alone to interpret
spectra may not be sufficient to capture the full complexity available through
JWST observations.Comment: 21 pages, 18 figures, submitted to A&A on 22. November 2022, in
review since 8. December 202
Circulation Flows: Cooling Flows with Bubble Return
The failure of the XMM-Newton and Chandra X-ray telescopes to detect cooling
gas in elliptical galaxies and clusters of galaxies has led many to adopt the
position that the gas is not cooling at all and that heating by an active
nucleus in the central E or cD galaxy is sufficient to offset radiative
cooling. In this paper we explore an idealized limiting example of this point
of view in which hot, buoyant bubbles formed near the center return the
inflowing, radiatively cooling gas to distant regions in the flow. We show that
idealized steady state, centrally heated non-cooling flows can indeed be
constructed. In addition, the emission-weighted temperature profiles in these
circulating flows resemble those of normal cooling flows. However, these
solutions are valid only (1) for a range of bubble parameters for which there
is no independent justification, (2) for a limited spatial region in the
cooling flow and (3) for a limited period of time after which cooling seems
inevitable. Our exploration of non-cooling flows is set in the context of
galaxy/group flows.Comment: 10 pages (emulateapj5) with 4 figures; accepted by The Astrophysical
Journa
Topical tetracaine prior to arterial puncture: a randomized, placebo-controlled clinical trial
AbstractThe objective of this randomized, double-blind, placebo-controlled clinical trial was to determine whether a topical anesthetic agent (tetracaine) provides effective local analgesia prior to radial arterial puncture. Tetracaine or placebo gel was applied 45min prior to arterial puncture to patients who were referred for elective arterial blood gas. The primary outcome was the patient's perception of pain associated with the procedure as measured by a visual analog scale. Fifty patients were randomized into the study, 24 received tetracaine and 26 placebo. Mean pain score on the visual analog scale was 26.2±32.6 for the tetracaine-treated patients and 23.8±27.4 for the placebo-treated patients (P=0.78). Mean time from the first skin puncture to successful procurement of 1ml of arterial blood was 70±103s in the tetracaine group and 49±48s in the placebo group (P=0.40). Difficulty of arterial puncture as assessed by the respiratory therapist performing the test was identical for the two groups (P=0.86). We conclude that tetracaine gel did not decrease patient's perception of pain associated with arterial puncture, nor did its use facilitate the ABG procedure
The X-ray Size-Temperature Relation for Intermediate Redshift Galaxy Clusters
We present the first measurements of the X-ray size-temperature (ST) relation
in intermediate redshift (z~0.30) galaxy clusters. We interpret the local ST
relation (z~0.06) in terms of underlying scaling relations in the cluster dark
matter properties, and then we use standard models for the redshift evolution
of those dark matter properties to show that the ST relation does not evolve
with redshift. We then use ROSAT HRI observations of 11 clusters to examine the
intermediate redshift ST relation; for currently favored cosmological
parameters, the intermediate redshift ST relation is consistent with that of
local clusters. Finally, we use the ST relation and our evolution model to
measure angular diameter distances; with these 11 distances we evaluate
constraints on Omega_M and Omega_L which are consistent with those derived from
studies of Type Ia supernovae. The data rule out a model with Omega_M=1 and
Omega_L=0 with 2.5 sigma confidence. When limited to models where
Omega_M+Omega_L=1, these data are inconsistent with Omega_M=1 with 3 sigma
confidence.Comment: ApJ: submitted April 7, accepted June 28, to appear Dec 1 (vol 544
XMM-Newton and Chandra Observations of the Galaxy Group NGC 5044. I. Evidence for Limited Multi-Phase Hot Gas
Using new XMM and Chandra observations we present an analysis of the
temperature structure of the hot gas within a radius of 100 kpc of the bright
nearby galaxy group NGC 5044. A spectral deprojection analysis of data
extracted from circular annuli reveals that a two-temperature model (2T) of the
hot gas is favored over single-phase or cooling flow (M_dot = 4.5 +/- 0.2
M_{sun}/yr) models within the central ~30 kpc. Alternatively, the data can be
fit equally well if the temperature within each spherical shell varies
continuously from ~T_h to T_c ~ T_h/2, but no lower. The high spatial
resolution of the Chandra data allows us to determine that the temperature
excursion T_h --> T_c required in each shell exceeds the temperature range
between the boundaries of the same shell in the best-fitting single-phase
model. This is strong evidence for a multi-phase gas having a limited
temperature range. The cooler component of the 2T model has a temperature (T_c
\~ 0.7 keV) similar to the kinetic temperature of the stars. The hot phase has
a temperature (T_h ~ 1.4 keV) characteristic of the virial temperature of the
\~10^{13} M_{sun} halo expected in the NGC 5044 group. However, in view of the
morphological disturbances and X-ray holes visible in the Chandra image within
R ~10 kpc, bubbles of gas heated to ~T_h in this region may be formed by
intermittent AGN feedback. Some additional heating at larger radii may be
associated with the evolution of the cold front near R ~50 kpc, as suggested by
the sharp edge in the EPIC images.Comment: 18 pages, 10 figures, Accepted for publication in ApJ, some changes
in presentation for consistency with paper 2 (astro-ph/0303054), includes
detailed analysis of azimuthal spectral variations in the chandra image,
conclusions unchanged from previous versio
Key Data Gaps for Understanding Trends in Prescription Opioid Analgesic Abuse and Diversion Among Chronic Pain Patients and Nonmedical Users
Population dynamics of medical and nonmedical prescription opioid usage and adverse outcomes were modeled. Critical parameter values were determined by their amount of influence on model behavior. Results suggest that closing these data gaps would help researchers to better identify ways to reduce the risk of adverse outcomes
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