1,193 research outputs found
Dense Gas in the Milky Way
We present a study of dense gas emission in the Milky Way in order to serve
as a basis for comparison with extragalactic results. This study combines new
observations of HCN, CS, and CO in individual GMCs and in the Milky Way plane
with published studies of emission from these molecules in the inner 500 pc of
the Milky Way. We find a strong trend in the fraction of emission from dense
gas tracers as a function of location in the Milky Way: in the bulge,
I_{HCN}/I_{CO} = 0.081 \pm 0.004, in the plane, I_{HCN}/I_{CO} = 0.026 \pm
0.008 on average, and over the full extent of nearby GMCs, I_{HCN}/I_{CO} =
0.014 \pm 0.020. Similar trends are seen in I_{CS}/I_{CO}. The low intensities
of the HCN and CS emission in the plane suggests that these lines are produced
by gas at moderate densities; they are thus not like the emission produced by
the dense, pc-scale star forming cores in nearby GMCs. The contrast between the
bulge and disk ratios in the Milky Way is likely to be caused by a combination
of higher kinetic temperatures as well as a higher dense gas fraction in the
bulge of the Milky Way.Comment: 34 pages LaTeX, AASTEX macros, includes 11 postscript figures. To
appear in ApJ 478, March 199
The Spiral Structure of the Outer Milky Way in Hydrogen
We produce a detailed map of the perturbed surface density of neutral
hydrogen in the outer Milky Way disk demonstrating that the Galaxy is a
non-axisymmetric multi-armed spiral. Spiral structure in the southern half of
the Galaxy can be traced out to at least 25 kpc, implying a minimum radius for
the gas disk. Overdensities in the surface density are coincident with regions
of reduced gas thickness. The ratio of the surface density to the local median
surface density is relatively constant along an arm. Logarithmic spirals can be
fit to the arms with pitch angles of 20-25 degrees.Comment: 10 pages with 4 color figures. Accepted for publication in Science.
Embargoed for discussion in the popular press until publication in
ScienceXpress. Higher resolution versions of figures 3 and 4 are available at
http://astron.berkeley.edu/~elevin
Interaction of laser generated ultrasonic waves with wedge-shaped samples
Wedge-shaped samples can be used as a model of acoustic interactions with samples ranging from ocean wedges, to angled defects such as rolling contact fatigue, to thickness measurements of samples with non-parallel faces. We present work on laser generated ultrasonic waves on metal samples; one can measure the dominant Rayleigh-wave mode, but longitudinal and shear waves are also generated. We present calculations, models, and measurements giving the dependence of the arrival times and amplitudes of these modes on the wedge apex angle and the separation of generation and detection points, and hence give a measure of the wedge characteristics
A Magellanic Origin for the Warp of the Galaxy
We show that a Magellanic Cloud origin for the warp of the Milky Way can
explain most quantitative features of the outer HI layer recently identified by
Levine, Blitz & Heiles (2005). We construct a model similar to that of Weinberg
(1998) that produces distortions in the dark matter halo, and we calculate the
combined effect of these dark-halo distortions and the direct tidal forcing by
the Magellanic Clouds on the disk warp in the linear regime. The interaction of
the dark matter halo with the disk and resonances between the orbit of the
Clouds and the disk account for the large amplitudes observed for the vertical
m=0,1,2 harmonics. The observations lead to six constraints on warp forcing
mechanisms and our model reasonably approximates all six. The disk is shown to
be very dynamic, constantly changing its shape as the Clouds proceed along
their orbit. We discuss the challenges to MOND placed by the observations.Comment: 4 pages, 3 figures, submitted to ApJ Letters. Additional graphics, 3d
visualizations and movies available at
http://www.astro.umass.edu/~weinberg/lm
Jeans analysis of self-gravitating systems in f(R)-gravity
Dynamics and collapse of collisionless self-gravitating systems is described
by the coupled collisionless Boltzmann and Poisson equations derived from
-gravity in the weak field approximation. Specifically, we describe a
system at equilibrium by a time-independent distribution function
and two potentials and solutions of the modified
Poisson and collisionless Boltzmann equations. Considering a small perturbation
from the equilibrium and linearizing the field equations, it can be obtained a
dispersion relation. A dispersion equation is achieved for neutral
dust-particle systems where a generalized Jeans wave-number is obtained. This
analysis gives rise to unstable modes not present in the standard Jeans
analysis (derived assuming Newtonian gravity as weak filed limit of ).
In this perspective, we discuss several self-gravitating astrophysical systems
whose dynamics could be fully addressed in the framework of -gravity.Comment: 8 pages, 2 figures, Accepted for publication in PR
High-Resolution Measurements of the Dark Matter Halo of NGC 2976: Evidence for a Shallow Density Profile
We have obtained two-dimensional velocity fields of the dwarf spiral galaxy
NGC 2976 in Halpha and CO. The high spatial (~75 pc) and spectral (13 km/s and
2 km/s, respectively) resolution of these observations, along with our
multicolor optical and near-infrared imaging, allow us to measure the shape of
the density profile of the dark matter halo with good precision. We find that
the total (baryonic plus dark matter) mass distribution of NGC 2976 follows a
rho_tot ~ r^(-0.27 +/- 0.09) power law out to a radius of 1.8 kpc, assuming
that the observed radial motions provide no support. The density profile
attributed to the dark halo is even shallower, consistent with a nearly
constant density of dark matter over the entire observed region. A maximal disk
fit yields an upper limit to the K-band stellar mass-to-light ratio (M*/L_K) of
0.09^{+0.15}_{-0.08} M_sun/L_sun,K (including systematic uncertainties), with
the caveat that for M*/L_K > 0.19 M_sun/L_sun,K the dark matter density
increases with radius, which is unphysical. Assuming 0.10 M_sun/L_sun,K <
M*/L_K < 0.19 M_sun/L_sun,K, the dark matter density profile lies between
rho_dm ~ r^-0.17 and rho_dm ~ r^-0.01. Therefore, independent of any
assumptions about the stellar disk or the functional form of the density
profile, NGC 2976 does not contain a cuspy dark matter halo. We also
investigate some of the systematic effects that can hamper rotation curve
studies, and show that 1) longslit rotation curves are far more vulnerable to
systematic errors than two-dimensional velocity fields, 2) NGC 2976 contains
large radial motions at small radii, and 3) the Halpha and CO velocity fields
of NGC 2976 agree within their uncertainties. [slightly abridged]Comment: 30 pages, 4 tables, 13 figures (7 in color; Figures 1 and 3 are
low-resolution to save space). Accepted for publication in ApJ. Version with
full-resolution figures available at
http://astro.berkeley.edu/~bolatto/ngc2976rotation.ps (46 MB
Adherence and Acceptability of Telehealth Appointments for High Risk Obstetrical Patients During the COVID-19 Pandemic.
Background:Telehealth has been successfully implemented for the delivery of obstetrical care. However, little is known regarding the attitudes and acceptability of patients and providers in high risk obstetrics and if implementation improves access to care in non-rural settings. Objective:The study aims to: 1) Describe patient and provider attitudes toward telehealth for delivery of high risk obstetrical care in a large health care system with both urban and suburban settings. 2) Determine if implementation of a telehealth model improves patient adherence to scheduled appointments in this patient population.Study DesignTwo self-administered surveys were designed. The first survey was sent to all high-risk obstetrical patients who received a telehealth visit between March 1, 2020 and May 30, 2020. The second survey was designed for providers who participated in these visits. We also compared the attended, cancelled and no show visit rates before (March 1-May 30, 2019) and after (March 1-May 30, 2020) telehealth implementation, as well as telehealth versus in person visits in 2020. We reviewed scheduled high-risk prenatal care appointments, diabetes education sessions, and genetic counseling and Maternal- Fetal Medicine consultations. Results:A total of 91 patient surveys and 33 provider surveys were analyzed. Overall, 86.9% of patients were satisfied with the care they received and 78.3% would recommend telehealth visits to others. 87.8% of providers reported having a positive experience using telehealth, and 90.9% believed that telehealth improved patients\u27 access to care. When comparing patient and provider preference regarding future obstetrical care after experiencing telehealth, 73.8% of patients desired a combination of in person and telehealth visits during their pregnancy. However, a significantly higher rate of providers preferred in-person visits (56% vs 23% respectively). When comparing visits between 2019 and 2020, there was a significantly lower rate of no-show appointments, patient-cancelled appointments, and patient same-day cancellations with the implementation of telehealth. There was also a significantly lower rate of patient-cancelled appointments, and patient same-day cancellations with those receiving telehealth visits compared to in person visits in 2020. Conclusion:Implementation of telehealth in high risk obstetrics has the potential to improve access to high risk obstetrical care, by reducing the rate of missed appointments. Both patients and providers surveyed expressed a high rate of satisfaction with telehealth visits and a desire to integrate telehealth into the traditional model of high risk obstetrical care
Molecular gas at supernova local environments unveiled by EDGE
CO observations allow estimations of the gas content of molecular clouds,
which trace the reservoir of cold gas fuelling star formation, as well as to
determine extinction via H column density, N(H). Here, we studied
millimetric and optical properties at 26 supernovae (SNe) locations of
different types in a sample of 23 nearby galaxies by combining molecular
CO (J = 1 0) resolved maps from the EDGE survey and
optical Integral Field Spectroscopy from the CALIFA survey. We found an even
clearer separation between type II and type Ibc SNe in terms of molecular gas
than what we found in the optical using H emission as a proxy for
current SF rate, which reinforces the fact that SNe Ibc are more associated
with SF-environments. While A at SN locations is similar for SNe II and SNe
Ibc, and higher compared to SNe Ia, N(H) is significantly higher for SNe
Ibc than for SNe II and SNe Ia. When compared to alternative extinction
estimations directly from SN photometry and spectroscopy, we find that our SNe
Ibc have also redder color excess but showed standard Na I D absorption
pseudo-equivalent widths (1 \AA). In some cases we find no extinction
when estimated from the environment, but high amounts of extinction when
measured from SN observations, which suggests that circumstellar material or
dust sublimation may be playing a role. This work serves as a benchmark for
future studies combining last generation millimeter and optical IFS instruments
to reveal the local environmental properties of extragalactic SNe.Comment: MNRAS accepted, 17 pages, 8 Figures, 4 Table
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