3,049 research outputs found
Galaxy Kinematics With Virus-P: The Dark Matter Halo Of M87
We present two-dimensional stellar kinematics of M87 out to R = 238 '' taken with the integral field spectrograph VIRUS-P. We run a large set of axisymmetric, orbit-based dynamical models and find clear evidence for a massive dark matter halo. While a logarithmic parameterization for the dark matter halo is preferred, we do not constrain the dark matter scale radius for a Navarro-Frenk-White (NFW) profile and therefore cannot rule it out. Our best-fit logarithmic models return an enclosed dark matter fraction of 17.2(-5.0)(+5.0)% within one effective radius (R-e congruent to 100 ''), rising to 49.4(-8.8)(+7.2)% within 2 R-e. Existing SAURON data (R <= 13 ''), and globular cluster (GC) kinematic data covering 145 '' <= R <= 554 '' complete the kinematic coverage to R = 47 kpc (similar to 5R(e)). At this radial distance, the logarithmic dark halo comprises 85.3(-2.4)(+2.5)% of the total enclosed mass of 5.7(-0.9)(+1.3) x 10(12) M-circle dot making M87 one of the most massive galaxies in the local universe. Our best-fit logarithmic dynamical models return a stellar mass-to-light ratio (M/L) of 9.1(-0.2)(+0.2) (V band), a dark halo circular velocity of 800(-25)(+75) km s(-1), and a dark halo scale radius of 36(-3)(+7) kpc. The stellar M/L, assuming an NFW dark halo, is well constrained to 8.20(-0.10)(+0.05) (V band). The stars in M87 are found to be radially anisotropic out to R congruent to 0.5 R-e, then isotropic or slightly tangentially anisotropic to our last stellar data point at R = 2.4 R-e where the anisotropy of the stars and GCs are in excellent agreement. The GCs then become radially anisotropic in the last two modeling bins at R = 3.4 R-e and R = 4.8 R-e. As one of the most massive galaxies in the local universe, constraints on both the mass distribution of M87 and anisotropy of its kinematic components strongly inform our theories of early-type galaxy formation and evolution in dense environments.Astronom
A New Z=0 Metagalactic Ultraviolet Background Limit
We present new integral-field spectroscopy in the outskirts of two nearby, edge-on, late-type galaxies to search for the H alpha emission that is expected from the exposure of their hydrogen gas to the metagalactic ultraviolet background (UVB). Despite the sensitivity of the VIRUS-P spectrograph on the McDonald 2.7 m telescope to low surface brightness emission and the large field of view, we do not detect H alpha to 5 sigma upper limits of 6.4 x 10(-19) erg s(-1) cm(-2) arcsec(-2) in UGC 7321 and of 25 x 10(-19) erg s(-1) cm(-2) arcsec(-2) in UGC 1281 in each of the hundreds of independent spatial elements (fibers). We fit gas distribution models from overlapping 21 cm data of HI, extrapolate one scale length beyond the HI data, and estimate predicted H alpha surface brightness maps. We analyze three types of limits from the data with stacks formed from increasingly large spatial regions and compare to the model predictions: (1) single fibers, (2) convolution of the fiber grid with a Gaussian, circular kernel (10('') full width at half-maximum), and (3) the co-added spectra from a few hundred fibers over the brightest model regions. None of these methods produce a significant detection (>5 sigma) with the most stringent constraints on the Hi photoionization rate of Gamma(z = 0) < 1.7 x 10(-14) s(-1) in UGC 7321 and Gamma(z = 0) < 14 x 10(-14) s(-1) in UGC 1281. The UGC 7321 limit is below previous measurement limits and also below current theoretical models. Restricting the analysis to the fibers bound by the HI data leads to a comparable limit; the limit is Gamma(z = 0) < 2.3 x 10(-14) s(-1) in UGC 7321. We discuss how a low Lyman limit escape fraction in z similar to 0 redshift star-forming galaxies might explain this lower than predicted UVB strength and the prospects of deeper data to make a direct detection.U.S. Government NAG W-2166National Science FoundationUT David BrutonTexas Norman Hackerman Advanced Research Program 003658-0295-2007Cynthia and George Mitchell FoundationMcDonald Observator
B2 0902+34: A Collapsing Protogiant Elliptical Galaxy at z=3.4
We have used the visible integral-field replicable unit spectrograph
prototype (VIRUS-P), a new integral field spectrograph, to study the spatially
and spectrally resolved Lyman-alpha emission line structure in the radio galaxy
B2 0902+34 at z=3.4. We observe a halo of Lyman-alpha emission with a velocity
dispersion of 250 km/s extending to a radius of 50 kpc. A second feature is
revealed in a spatially resolved region where the line profile shows
blueshifted structure. This may be viewed as either HI absorption at -450 km/s
or secondary emission at -900 km/s from the primary peak. Our new data, in
combination with the 21 cm absorption, suggest two important and unexplained
discrepancies. First, nowhere in the line profiles of the Lyman-alpha halo is
the 21 cm absorber population evident. Second, the 21 cm absorption redshift is
higher than the Lyman-alpha emission redshift. In an effort to explain these
two traits, we have undertaken the first three dimensional Monte Carlo
simulations of resonant scattering in radio galaxies. Though simple, the model
produces the features in the Lyman-alpha data and predicts the 21 cm
properties. To reach agreement between this model and the data, global infall
of the HI is strictly necessary. The amount of gas necessary to match the model
and data is surprisingly high, >= 10E12 solar masses, an order of magnitude
larger than the stellar mass. The collapsing structure and large gas mass lead
us to interpret B2 0902+34 as a protogiant elliptical galaxy.Comment: 30 pages, 8 figures, 4 tables, accepted in Ap
Well-being among Older Adults in Mississippi: Exploring Differences between Metropolitan, Micropolitan, and Noncore Rural Settings
It is a common belief that older adults in rural areas have high subjective well-being, despite often experiencing greater poverty and having access to fewer resources than older adults who live in urban areas, a phenomenon sometimes referred to as the “rural-urban paradox.” However, research does not consistently find high well-being in rural areas, which might be due to research not distinguishing between very rural and semi-rural (or small town) settings. This study compares the subjective well-being of older adults in micropolitan and noncore counties with the well-being of older adults in metropolitan areas in Mississippi (n = 659). Preliminary results indicate metropolitan respondents reporting higher subjective well-being than both micropolitan and noncore respondents. However, after accounting for key covariates, micropolitan residents were found to have significantly lower levels of subjective well- being compared to metropolitan residents. Overall, our study suggests that micropolitan settings may be less conducive to healthy, successful aging when compared to metropolitan settings
Dusty OB stars in the Small Magellanic Cloud - II: Extragalactic Disks or Examples of the Pleiades Phenomenon?
We use mid-infrared Spitzer spectroscopy and far-infrared Herschel photometry
for a sample of twenty main sequence O9--B2 stars in the Small Magellanic Cloud
(SMC) with strong 24 micron excesses to investigate the origin of the mid-IR
emission. Either debris disks around the stars or illuminated patches of dense
interstellar medium (ISM) can cause such mid-IR emission. In a companion paper,
Paper I, we use optical spectroscopy to show that it is unlikely for any of
these sources to be classical Be stars or Herbig Ae/Be stars. We focus our
analysis on debris disks and cirrus hot spots. We find three out of twenty
stars to be significantly extended in the mid-IR, establishing them as cirrus
hot spots. We then fit the IR spectral energy distributions to determine dust
temperatures and masses. We find the dust masses in the SMC stars to be larger
than for any known debris disks, although this evidence against the debris disk
hypothesis is circumstantial. Finally, we created a local comparison sample of
bright mid-IR OB stars in the Milky Way (MW) by cross-matching the WISE and
Hipparcos catalogs. All such local stars in the appropriate luminosity range
that can be unambiguously classified are young stars with optical emission
lines or are spatially resolved by WISE with sizes too large to be plausible
debris disk candidates. We conclude that the very strong mid-IR flux excesses
are most likely explained as cirrus hot spots, although we cannot rigorously
rule out that a small fraction of the sample is made up of debris disks or
transition disks. We present suggestive evidence that bow-shock heating around
runaway stars may be a contributing mechanism to the interstellar emission.
These sources, interpreted as cirrus hot spots, offer a new localised probe of
diffuse interstellar dust in a low metallicity environment. (Abridged)Comment: Accepted for publication in ApJ, 23 pages, 11 figures, 8 table
Indicators of Supportive Service Need Among Older Adults in Mississippi
Providing quality services is one of the challenges associated with the continued increase in the nation’s older adult population. Effective use of needs assessment data can be useful in assessing service need. This study measures the level of perceived need for supportive services among older adults in Mississippi. Using statewide needs assessment data, this study applies the Behavioral Model to measure the perceived need for supportive services among survey participants aged 60 and older (N = 838). Results indicate that age, race, physical health, and subjective well-being were consistent predictors of perceived need for supportive services. Results suggest the importance of understanding the factors associated with the perceived need for supportive services to more effectively plan service delivery
Mass production of volume phase holographic gratings for the VIRUS spectrograph array
The Visible Integral-field Replicable Unit Spectrograph (VIRUS) is a baseline
array of 150 copies of a simple, fiber-fed integral field spectrograph that
will be deployed on the Hobby-Eberly Telescope (HET). VIRUS is the first
optical astronomical instrument to be replicated on an industrial scale, and
represents a relatively inexpensive solution for carrying out large-area
spectroscopic surveys, such as the HET Dark Energy Experiment (HETDEX). Each
spectrograph contains a volume phase holographic (VPH) grating with a 138 mm
diameter clear aperture as its dispersing element. The instrument utilizes the
grating in first-order for 350-550 nm. Including witness samples, a suite of
170 VPH gratings has been mass produced for VIRUS. Here, we present the design
of the VIRUS VPH gratings and a discussion of their mass production. We
additionally present the design and functionality of a custom apparatus that
has been used to rapidly test the first-order diffraction efficiency of the
gratings for various discrete wavelengths within the VIRUS spectral range. This
device has been used to perform both in-situ tests to monitor the effects of
adjustments to the production prescription as well as to carry out the final
acceptance tests of the gratings' diffraction efficiency. Finally, we present
the as-built performance results for the entire suite of VPH gratings.Comment: 16 pages, 11 figures, 2 tables. To be published in Proc. SPIE, 2014,
"Advances in Optical and Mechanical Technologies for Telescopes and
Instrumentation", 9151-53. The work presented in this article follows from
arXiv:1207:448
Chemical Signatures of the First Supernovae in the Sculptor Dwarf Spheroidal Galaxy
We present a homogeneous chemical abundance analysis of five of the most
metal-poor stars in the Sculptor dwarf spheroidal galaxy. We analyze new and
archival high resolution spectroscopy from Magellan/MIKE and VLT/UVES and
determine stellar parameters and abundances in a consistent way for each star.
Two of the stars in our sample, at [Fe/H] = -3.5 and [Fe/H] = -3.8, are new
discoveries from our Ca K survey of Sculptor, while the other three were known
in the literature. We confirm that Scl 07-50 is the lowest metallicity star
identified in an external galaxy, at [Fe/H] = -4.1. The two most metal-poor
stars both have very unusual abundance patterns, with striking deficiencies of
the alpha elements, while the other three stars resemble typical extremely
metal-poor Milky Way halo stars. We show that the star-to-star scatter for
several elements in Sculptor is larger than that for halo stars in the same
metallicity range. This scatter and the uncommon abundance patterns of the
lowest metallicity stars indicate that the oldest surviving Sculptor stars were
enriched by a small number of earlier supernovae, perhaps weighted toward
high-mass progenitors from the first generation of stars the galaxy formed.Comment: 11 pages, 2 figures, 4 tables (2 landscape tables are at the end; for
full tables, contact first author or wait for published version). Accepted
for publication in Ap
Dwarf Galaxy Dark Matter Density Profiles Inferred from Stellar and Gas Kinematics
We present new constraints on the density profiles of dark matter (DM) halos
in seven nearby dwarf galaxies from measurements of their integrated stellar
light and gas kinematics. The gas kinematics of low mass galaxies frequently
suggest that they contain constant density DM cores, while N-body simulations
instead predict a cuspy profile. We present a data set of high resolution
integral field spectroscopy on seven galaxies and measure the stellar and gas
kinematics simultaneously. Using Jeans modeling on our full sample, we examine
whether gas kinematics in general produce shallower density profiles than are
derived from the stars. Although 2/7 galaxies show some localized differences
in their rotation curves between the two tracers, estimates of the central
logarithmic slope of the DM density profile, gamma, are generally robust. The
mean and standard deviation of the logarithmic slope for the population are
gamma=0.67+/-0.10 when measured in the stars and gamma=0.58+/-0.24 when
measured in the gas. We also find that the halos are not under concentrated at
the radii of half their maximum velocities. Finally, we search for correlations
of the DM density profile with stellar velocity anisotropy and other baryonic
properties. Two popular mechanisms to explain cored DM halos are an exotic DM
component or feedback models that strongly couple the energy of supernovae into
repeatedly driving out gas and dynamically heating the DM halos. We investigate
correlations that may eventually be used to test models. We do not find a
secondary parameter that strongly correlates with the central DM density slope,
but we do find some weak correlations. Determining the importance of these
correlations will require further model developments and larger observational
samples. (Abridged)Comment: 29 pages, 18 figures, 10 tables, accepted for publication in Ap
Boolean Chaos
We observe deterministic chaos in a simple network of electronic logic gates
that are not regulated by a clocking signal. The resulting power spectrum is
ultra-wide-band, extending from dc to beyond 2 GHz. The observed behavior is
reproduced qualitatively using an autonomously updating Boolean model with
signal propagation times that depend on the recent history of the gates and
filtering of pulses of short duration, whose presence is confirmed
experimentally. Electronic Boolean chaos may find application as an
ultra-wide-band source of radio wavesComment: 10 pages and 4 figur
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