7,969 research outputs found
A General Precipitation-Limited L_X-T-R Relation Among Early-Type Galaxies
The relation between X-ray luminosity (L_X) and ambient gas temperature (T)
among massive galactic systems is an important cornerstone of both
observational cosmology and galaxy-evolution modeling. In the most massive
galaxy clusters, the relation is determined primarily by cosmological structure
formation. In less massive systems, it primarily reflects the feedback response
to radiative cooling of circumgalactic gas. Here we present a simple but
powerful model for the L_X-T relation as a function of physical aperture R
within which those measurements are made. The model is based on the
precipitation framework for AGN feedback and assumes that the circumgalactic
medium is precipitation-regulated at small radii and limited by cosmological
structure formation at large radii. We compare this model with many different
data sets and show that it successfully reproduces the slope and upper envelope
of the L_X-T-R relation over the temperature range from ~0.2 keV through >10
keV. Our findings strongly suggest that the feedback mechanisms responsible for
regulating star formation in individual massive galaxies have much in common
with the precipitation-triggered feedback that appears to regulate
galaxy-cluster cores.Comment: Submitted to ApJ, 9 pages, 3 figures (v2 fixes a few small typos
The MASSIVE Survey - III. Molecular gas and a broken Tully-Fisher relation in the most massive early-type galaxies
In this work we present CO(1-0) and CO(2-1) observations of a pilot sample of
15 early-type galaxies (ETGs) drawn from the MASSIVE galaxy survey, a
volume-limited integral-field spectroscopic study of the most massive ETGs
() within 108 Mpc. These objects were selected because
they showed signs of an interstellar medium and/or star formation. A large
amount of gas (210 M) is present in 10 out of 15
objects, and these galaxies have gas fractions higher than expected based on
extrapolation from lower mass samples. We tentatively interpret this as
evidence that stellar mass loss and hot halo cooling may be starting to play a
role in fuelling the most massive galaxies. These MASSIVE ETGs seem to have
lower star-formation efficiencies (SFE=SFR/M) than spiral galaxies,
but the SFEs derived are consistent with being drawn from the same distribution
found in other lower mass ETG samples. This suggests that the SFE is not simply
a function of stellar mass, but that local, internal processes are more
important for regulating star formation. Finally we used the CO line profiles
to investigate the high-mass end of the Tully-Fisher relation (TFR). We find
that there is a break in the slope of the TFR for ETGs at high masses
(consistent with previous studies). The strength of this break correlates with
the stellar velocity dispersion of the host galaxies, suggesting it is caused
by additional baryonic mass being present in the centre of massive ETGs. We
speculate on the root cause of this change and its implications for galaxy
formation theories.Comment: 13 pages, 7 figures, accepted by MNRA
The Effect of Spatial Gradients in Stellar Mass-to-Light Ratio on Black Hole Mass Measurements
We have tested the effect of spatial gradients in stellar mass-to-light ratio
(Y) on measurements of black hole masses (MBH) derived from stellar orbit
superposition models. Such models construct a static gravitational potential
for a galaxy and its central black hole, but typically assume spatially uniform
Y. We have modeled three giant elliptical galaxies with gradients alpha = d(log
Y)/d(log r) from -0.2 to +0.1. Color and line strength gradients suggest mildly
negative alpha in these galaxies. Introducing a negative (positive) gradient in
Y increases (decreases) the enclosed stellar mass near the center of the galaxy
and leads to systematically smaller (larger) MBH measurements. For models with
alpha = -0.2, the best-fit values of MBH are 28%, 27%, and 17% lower than the
constant-Y case, in NGC 3842, NGC 6086, and NGC 7768, respectively. For alpha =
+0.1, MBH are 14%, 22%, and 17% higher than the constant-Y case for the three
respective galaxies. For NGC 3842 and NGC 6086, this bias is comparable to the
statistical errors from individual modeling trials. At larger radii, negative
(positive) gradients in Y cause the total stellar mass to decrease (increase)
and the dark matter fraction within one effective radius to increase
(decrease).Comment: 6 pages, 4 figures, 1 table. To appear in ApJ
The MASSIVE Survey - VIII. Stellar Velocity Dispersion Profiles and Environmental Dependence of Early-Type Galaxies
We measure the radial profiles of the stellar velocity dispersions,
, for 90 early-type galaxies (ETGs) in the MASSIVE survey, a
volume-limited integral-field spectroscopic (IFS) galaxy survey targeting all
northern-sky ETGs with absolute -band magnitude mag, or
stellar mass , within 108 Mpc. Our wide-field
107" 107" IFS data cover radii as large as 40 kpc, for which we
quantify separately the inner (2 kpc) and outer (20 kpc) logarithmic slopes
and of . While
is mostly negative, of the 56 galaxies with sufficient
radial coverage to determine we find 36% to have rising
outer dispersion profiles, 30% to be flat within the uncertainties, and 34% to
be falling. The fraction of galaxies with rising outer profiles increases with
and in denser galaxy environment, with 10 of the 11 most massive galaxies
in our sample having flat or rising dispersion profiles. The strongest
environmental correlations are with local density and halo mass, but a weaker
correlation with large-scale density also exists. The average is similar for brightest group galaxies, satellites, and isolated
galaxies in our sample. We find a clear positive correlation between the
gradients of the outer dispersion profile and the gradients of the velocity
kurtosis . Altogether, our kinematic results suggest that the increasing
fraction of rising dispersion profiles in the most massive ETGs are caused (at
least in part) by variations in the total mass profiles rather than in the
velocity anisotropy alone.Comment: Accepted/in press, MNRA
The MASSIVE Survey II: Stellar Population Trends Out to Large Radius in Massive Early Type Galaxies
We examine stellar population gradients in ~100 massive early type galaxies
spanning 180 < sigma* < 370 km/s and M_K of -22.5 to -26.5 mag, observed as
part of the MASSIVE survey (Ma et al. 2014). Using integral-field spectroscopy
from the Mitchell Spectrograph on the 2.7m telescope at McDonald Observatory,
we create stacked spectra as a function of radius for galaxies binned by their
stellar velocity dispersion, stellar mass, and group richness. With excellent
sampling at the highest stellar mass, we examine radial trends in stellar
population properties extending to beyond twice the effective radius (~2.5
R_e). Specifically, we examine trends in age, metallicity, and abundance ratios
of Mg, C, N, and Ca, and discuss the implications for star formation histories
and elemental yields. At a fixed physical radius of 3-6 kpc (the likely size of
the galaxy cores formed at high redshift) stellar age and [alpha/Fe] increase
with increasing sigma* and depend only weakly on stellar mass, as we might
expect if denser galaxies form their central cores earlier and faster. If we
instead focus on 1-1.5 R_e, the trends in abundance and abundance ratio are
washed out, as might be expected if the stars at large radius were accreted by
smaller galaxies. Finally, we show that when controlling for \sigmastar, there
are only very subtle differences in stellar population properties or gradients
as a function of group richness; even at large radius internal properties
matter more than environment in determining star formation history.Comment: 17 pages, 9 figures, accepted by ApJ; resubmitted with updated
reference
The MASSIVE Survey - I. A Volume-Limited Integral-Field Spectroscopic Study of the Most Massive Early-Type Galaxies within 108 Mpc
Massive early-type galaxies represent the modern-day remnants of the earliest
major star formation episodes in the history of the universe. These galaxies
are central to our understanding of the evolution of cosmic structure, stellar
populations, and supermassive black holes, but the details of their complex
formation histories remain uncertain. To address this situation, we have
initiated the MASSIVE Survey, a volume-limited, multi-wavelength,
integral-field spectroscopic (IFS) and photometric survey of the structure and
dynamics of the ~100 most massive early-type galaxies within a distance of 108
Mpc. This survey probes a stellar mass range M* > 10^{11.5} Msun and diverse
galaxy environments that have not been systematically studied to date. Our
wide-field IFS data cover about two effective radii of individual galaxies, and
for a subset of them, we are acquiring additional IFS observations on
sub-arcsecond scales with adaptive optics. We are also acquiring deep K-band
imaging to trace the extended halos of the galaxies and measure accurate total
magnitudes. Dynamical orbit modeling of the combined data will allow us to
simultaneously determine the stellar, black hole, and dark matter halo masses.
The primary goals of the project are to constrain the black hole scaling
relations at high masses, investigate systematically the stellar initial mass
function and dark matter distribution in massive galaxies, and probe the
late-time assembly of ellipticals through stellar population and kinematical
gradients. In this paper, we describe the MASSIVE sample selection, discuss the
distinct demographics and structural and environmental properties of the
selected galaxies, and provide an overview of our basic observational program,
science goals and early survey results.Comment: 19 pages, 14 figures. ApJ (2014) vol. 795, in pres
Variation in pediatric traumatic brain injury outcomes in the United States.
OBJECTIVE: To ascertain the degree of variation, by state of hospitalization, in outcomes associated with traumatic brain injury (TBI) in a pediatric population. DESIGN: A retrospective cohort study of pediatric patients admitted to a hospital with a TBI. SETTING: Hospitals from states in the United States that voluntarily participate in the Agency for Healthcare Research and Quality's Healthcare Cost and Utilization Project. PARTICIPANTS: Pediatric (age ≤ 19 y) patients hospitalized for TBI (N=71,476) in the United States during 2001, 2004, 2007, and 2010. INTERVENTIONS: None. MAIN OUTCOME MEASURES: Primary outcome was proportion of patients discharged to rehabilitation after an acute care hospitalization among alive discharges. The secondary outcome was inpatient mortality. RESULTS: The relative risk of discharge to inpatient rehabilitation varied by as much as 3-fold among the states, and the relative risk of inpatient mortality varied by as much as nearly 2-fold. In the United States, approximately 1981 patients could be discharged to inpatient rehabilitation care if the observed variation in outcomes was eliminated. CONCLUSIONS: There was significant variation between states in both rehabilitation discharge and inpatient mortality after adjusting for variables known to affect each outcome. Future efforts should be focused on identifying the cause of this state-to-state variation, its relationship to patient outcome, and standardizing treatment across the United States
The Potential of Teledentistry in Community Oral Health for the Pediatric Population
• Dental caries is the most prevalent chronic disease of childhood in the US. • Young children are a particularly vulnerable population because of their dependence, inability to communicate needs, and relative poverty. • Furthermore, this can be exacerbated by disparities such that an increased rates of caries are observed in children who are of low socioeconomic status and minority backgrounds. • However, community oral health screenings can play a vital role in childhood caries as a predominately preventable disease. • The current emphasis on social distance during the COVID-19 pandemic has brought attention to teledentistry, which may have a valuable role in the future of community oral health outreach
The MASSIVE Survey - VII. The Relationship of Angular Momentum, Stellar Mass and Environment of Early-Type Galaxies
We analyse the environmental properties of 370 local early-type galaxies
(ETGs) in the MASSIVE and ATLAS3D surveys, two complementary volume-limited
integral-field spectroscopic (IFS) galaxy surveys spanning absolute -band
magnitude , or stellar mass . We find these galaxies to reside in a diverse range of
environments measured by four methods: group membership (whether a galaxy is a
brightest group/cluster galaxy, satellite, or isolated), halo mass, large-scale
mass density (measured over a few Mpc), and local mass density (measured within
the th neighbour). The spatially resolved IFS stellar kinematics provide
robust measurements of the spin parameter and enable us to examine
the relationship among , , and galaxy environment. We find a
strong correlation between and , where the average
decreases from to below 0.1 with increasing mass, and the fraction
of slow rotators increases from % to 90%. We show for
the first time that at fixed , there are almost no trends between galaxy
spin and environment; the apparent kinematic morphology-density relation for
ETGs is therefore primarily driven by and is accounted for by the joint
correlations between and spin, and between and environment. A
possible exception is that the increased at high local density
is slightly more than expected based only on these joint correlations. Our
results suggest that the physical processes responsible for building up the
present-day stellar masses of massive galaxies are also very efficient at
reducing their spin, in any environment.Comment: Accepted to MNRA
Pancreaticoduodenal transplantation in humans
Whole cadaveric pancreata were transplanted to the pelvic extraperitoneal location in four patients with diabetes who previously had undergone successful cadaveric renal transplantation. One graft was lost within a few hours from venous thrombosis but with patient survival. The other three are providing normal endocrine function after two and a half, 11 and 12 months. The exocrine pancreatic secretions were drained into the recipient jejunum through enteric anastomoses. Because mucosal slough of the graft and duodenum and jejunum in two patients caused a protein losing enteropathy and necessitated reoperations, we now do the pancreatic transplantation with only a blister of graft duodenum large enough for side-to-side enteroenterostomy. The spleen has been transplanted with the pancreas mainly for technical reasons, and this technique should have further trials in spite of the fact that delayed graft splenectomy became necessary in two recipients to treat graft induced hematologic complications
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