2,747 research outputs found
Dynamical Masses in Luminous Infrared Galaxies
We have studied the dynamics and masses of a sample of ten nearby luminous
and ultraluminous infrared galaxies (LIRGS and ULIRGs), using 2.3 micron CO
absorption line spectroscopy and near-infrared H- and Ks-band imaging. By
combining velocity dispersions derived from the spectroscopy, disk
scale-lengths obtained from the imaging, and a set of likely model density
profiles, we calculate dynamical masses for each LIRG. For the majority of the
sample, it is difficult to reconcile our mass estimates with the large amounts
of gas derived from millimeter observations and from a standard conversion
between CO emission and H_2 mass. Our results imply that LIRGs do not have huge
amounts of molecular gas (10^10-10^11 Msolar) at their centers, and support
previous indications that the standard conversion of CO to H_2 probably
overestimates the gas masses and cannot be used in these environments. This in
turn suggests much more modest levels of extinction in the near-infrared for
LIRGs than previously predicted (A_V~10-20 versus A_V~100-1000). The lower gas
mass estimates indicated by our observations imply that the star formation
efficiency in these systems is very high and is triggered by cloud-cloud
collisions, shocks, and winds rather than by gravitational instabilities in
circumnuclear gas disks.Comment: 14 pages, 2 figures, accepted to Ap
A NASTRAN trainer for dynamics
Presented here is an automated training tool that engineers can use to master the application of NASTRAN to dynamic problems. Example problems were selected to make classical solutions available for comparison. These comparisons can be used to evaluate the solution
Associations between anxiety, body mass index, and sex hormones in women
Background: Several studies have shown a positive association between anxiety and obesity, particularly in women. We aimed to study whether sex hormone alterations related to obesity might play a role in this association. Patients and methods: Data for this study were obtained from a population-based cohort study (the LIFE-Adult-Study). A total of 3,124 adult women (970 premenopausal and 2,154 postmenopausal) were included into the analyses. The anxiety symptomatology was assessed using the GAD-7 questionnaire (cut-off ≥ 10 points). Sex hormones were measured from fasting serum samples. Results: We did not find significant differences in anxiety prevalence in premenopausal obese women compared with normal-weight controls (4.8% vs. 5.5%). Both obesity and anxiety symptomatology were separately associated with the same sex hormone alteration in premenopausal women: higher total testosterone level (0.97 ± 0.50 in obese vs. 0.86 ± 0.49 nmol/L in normal-weight women, p = 0.026 and 1.04 ± 0.59 in women with vs. 0.88 ± 0.49 nmol/L in women without anxiety symptomatology, p = 0.023). However, women with anxiety symptomatology had non-significantly higher estradiol levels than women without anxiety symptomatology (548.0 ± 507.6 vs. 426.2 ± 474.0 pmol/L), whereas obesity was associated with lower estradiol levels compared with those in normal-weight group (332.7 ± 386.5 vs. 470.8 ± 616.0 pmol/L). Women with anxiety symptomatology had also significantly higher testosterone and estradiol composition (p = 0.006). No associations of sex hormone levels and BMI with anxiety symptomatology in postmenopausal women were found. Conclusions: Although both obesity and anxiety symptomatology were separately associated with higher testosterone level, there was an opposite impact of anxiety and obesity on estradiol levels in premenopausal women. We did not find an evidence that the sex hormone alterations related to obesity are playing a significant role in anxiety symptomatology in premenopausal women. This could be the explanation why we did not find an association between obesity and anxiety. In postmenopausal women, other mechanisms seem to work than in the premenopausal group
Spitzer Observations of Cold Dust Galaxies
We combine new Spitzer Space Telescope observations in the mid- and
far-infrared with SCUBA 850 micron observations to improve the measurement of
dust temperatures, masses and luminosities for 11 galaxies of the SCUBA Local
Universe Galaxy Survey (SLUGS). By fitting dust models we measure typical dust
masses of 10E7.9 M_sol and dust luminosities of ~ 10E10 L_sol, for galaxies
with modest star formation rates. The data presented in this paper combined
with previous observations show that cold dust is present in all types of
spiral galaxies and is a major contributor to their total luminosity. Because
of the lower dust temperature of the SCUBA sources measured in this paper, they
have flatter Far-IR nu F_nu(160um)/nu F_nu(850um) slopes than the larger
Spitzer Nearby Galaxies Survey (SINGS), the sample that provides the best
measurements of the dust properties of galaxies in the nearby universe. The new
data presented here added to SINGS extend the parameter space that is well
covered by local galaxies, providing a comprehensive set of templates that can
be used to interpret the observations of nearby and distant galaxies.Comment: Accepted by A.J. 16 pages, 10 figures, 7 tables. High resolution
version at http://mips.as.arizona.edu/~cnaw/slugs_hires.pd
The Exozodiacal Dust Problem for Direct Observations of ExoEarths
Debris dust in the habitable zones of stars - otherwise known as exozodiacal
dust - comes from extrasolar asteroids and comets and is thus an expected part
of a planetary system. Background flux from the Solar System's zodiacal dust
and the exozodiacal dust in the target system is likely to be the largest
source of astrophysical noise in direct observations of terrestrial planets in
the habitable zones of nearby stars. Furthermore, dust structures like clumps,
thought to be produced by dynamical interactions with exoplanets, are a
possible source of confusion. In this paper, we qualitatively assess the
primary impact of exozodical dust on high-contrast direct imaging at optical
wavelengths, such as would be performed with a coronagraph. Then we present the
sensitivity of previous, current, and near-term facilities to thermal emission
from debris dust at all distances from nearby solar-type stars, as well as our
current knowledge of dust levels from recent surveys. Finally, we address the
other method of detecting debris dust, through high-contrast imaging in
scattered light. This method is currently far less sensitive than thermal
emission observations, but provides high spatial resolution for studying dust
structures. This paper represents the first report of NASA's Exoplanet
Exploration Program Analysis Group (ExoPAG).Comment: 21 pages, 5 figures, 2 tables. Accepted for publication in PASP
2012-06-0
Spitzer Observations of Low Luminosity Isolated and Low Surface Brightness Galaxies
We examine the infrared properties of five low surface brightness galaxies
(LSBGs) and compare them with related but higher surface brightness galaxies,
using Spitzer Space Telescope images and spectra. All the LSBGs are detected in
the 3.6 and 4.5um bands, representing the stellar population. All but one are
detected at 5.8 and 8.0um, revealing emission from hot dust and aromatic
molecules, though many are faint or point-like at these wavelengths. Detections
of LSBGs at the far-infrared wavelengths, 24, 70, and 160um, are varied in
morphology and brightness, with only two detections at 160um, resulting in
highly varied spectral energy distributions. Consistent with previous
expectations for these galaxies, we find that detectable dust components exist
for only some LSBGs, with the strength of dust emission dependent on the
existence of bright star forming regions. However, the far-infrared emission
may be relatively weak compared with normal star-forming galaxies.Comment: 20 pages, 8 figures, accepted to Ap
IR observations of MS 1054-03: Star Formation and its Evolution in Rich Galaxy Clusters
We study the infrared (IR) properties of galaxies in the cluster MS 1054-03
at z=0.83 by combining MIPS 24 micron data with spectra of more than 400
galaxies and a very deep K-band selected catalog. 19 IR cluster members are
selected spectroscopically, and an additional 15 are selected by their
photometric redshifts. We derive the IR luminosity function of the cluster and
find strong evolution compared to the similar-mass Coma cluster. The best
fitting Schechter function gives L*_{IR}=11.49 +0.30/-0.29 L_sun with a fixed
faint end slope, about one order of magnitude larger than that in Coma. The
rate of evolution of the IR luminosity from Coma to MS 1054-03 is consistent
with that found in field galaxies, and it suggests that some internal
mechanism, e.g., the consumption of the gas fuel, is responsible for the
general decline of the cosmic star formation rate (SFR) in different
environments. The mass-normalized integrated SFR within 0.5R_200 in MS 1054-03
also shows evolution compared with other rich clusters at lower redshifts, but
the trend is less conclusive if the mass selection effect is considered. A
nonnegligible fraction (13%) of cluster members, are forming stars actively and
the overdensity of IR galaxies is about 20 compared to the field. It is
unlikely that clusters only passively accrete star forming galaxies from the
surrounding fields and have their star formation quenched quickly afterward;
instead, many cluster galaxies still have large amounts of gas, and their star
formation may be enhanced by the interaction with the cluster.Comment: 49 pages, 9 figures, accepted by Ap
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