633 research outputs found
Global Properties of Neutral Hydrogen in Compact Groups
Compact groups of galaxies provide a unique environment to study the
evolution of galaxies amid frequent gravitational encounters. These nearby
groups have conditions similar to those in the earlier universe when galaxies
were assembled and give us the opportunity to witness hierarchical formation in
progress. To understand how the compact group environment affects galaxy
evolution, we examine the gas and dust in these groups. We present new
single-dish GBT neutral hydrogen (HI) observations of 30 compact groups and
define a new way to quantify the group HI content as the HI-to-stellar mass
ratio of the group as a whole. We compare the HI content with mid-IR indicators
of star formation and optical [g-r] color to search for correlations between
group gas content and star formation activity of individual group members.
Quiescent galaxies tend to live in HI-poor groups, and galaxies with active
star formation are more commonly found in HI-rich groups. Intriguingly, we also
find "rogue" galaxies whose star formation does not correlate with group HI
content. In particular, we identify three galaxies (NGC 2968 in RSCG 34, KUG
1131+202A in RSCG 42, and NGC 4613 in RSCG 64) whose mid-IR activity is
discrepant with the HI. We speculate that this mismatch between mid-IR activity
and HI content is a consequence of strong interactions in this environment that
can strip HI from galaxies and abruptly affect star-formation. Ultimately,
characterizing how and on what timescales the gas is processed in compact
groups will help us understand the interstellar medium in complex, dense
environments similar to the earlier Universe.Comment: Accepted to A
The Infrared Properties of Super Star Clusters: Predictions from Three-Dimensional Radiative Transfer Models
With high-resolution infrared data becoming available that can probe the
formation of high-mass stellar clusters for the first time, models that make
testable predictions of these objects are necessary. We utilize a
three-dimensional radiative transfer code, including a hierarchically clumped
medium, to study the earliest stages of super star cluster evolution. We
explore a range of parameter space in geometric sequences that mimic the
evolution of an embedded super star cluster. The inclusion of a hierarchically
clumped medium can make the envelope porous, in accordance with previous models
and supporting observational evidence. The infrared luminosity inferred from
observations can differ by a factor of two from the true value in the clumpiest
envelopes depending on the viewing angle. The infrared spectral energy
distribution also varies with viewing angle for clumpy envelopes, creating a
range in possible observable infrared colors and magnitudes, silicate feature
depths and dust continua. General observable features of cluster evolution
differ between envelopes that are relatively opaque or transparent to
mid-infrared photons. The [70]-[160] color can be used to determine star
formation efficiency; the Spitzer IRAC/MIPS [8.0]-[24] color is able to
constrain Rin and Rout values; and the IRAC [3.6]-[5.8] color is sensitive to
the fraction of the dust distributed in clumps. Finally, in a comparison of
these models to data of ultracompact HII regions, we find good agreement,
suggesting that these models are physically relevant, and will provide useful
diagnostic ability for datasets of resolved, embedded SSCs with the advent of
high-resolution infrared telescopes like JWST.Comment: ApJ, accepted, to be published in the 729 -1 issue. 17 pages with 18
figure
Effect of NASA Light-emitting Diode Irradiation on Wound Healing
Objective: The purpose of this study was to assess the effects of hyperbaric oxygen (HBO) and near-infrared light therapy on wound healing.
Background Data: Light-emitting diodes (LED), originally developed for NASA plant growth experiments in space show promise for delivering light deep into tissues of the body to promote wound healing and human tissue growth. In this paper, we review and present our new data of LED treatment on cells grown in culture, on ischemic and diabetic wounds in rat models, and on acute and chronic wounds in humans.
Materials and Methods: In vitro and in vivo (animal and human) studies utilized a variety of LED wavelength, power intensity, and energy density parameters to begin to identify conditions for each biological tissue that are optimal for biostimulation.
Results: LED produced in vitro increases of cell growth of 140–200% in mouse-derived fibroblasts, rat-derived osteoblasts, and rat-derived skeletal muscle cells, and increases in growth of 155–171% of normal human epithelial cells. Wound size decreased up to 36% in conjunction with HBO in ischemic rat models. LED produced improvement of greater than 40% in musculoskeletal training injuries in Navy SEAL team members, and decreased wound healing time in crew members aboard a U.S. Naval submarine. LED produced a 47% reduction in pain of children suffering from oral mucositis.
Conclusion: We believe that the use of NASA LED for light therapy alone, and in conjunction with hyperbaric oxygen, will greatly enhance the natural wound healing process, and more quickly return the patient to a preinjury/ illness level of activity. This work is supported and managed through the NASA Marshall Space Flight Center–SBIR Program
The Importance of Hands-on Experience with Telescopes for Students
Proper interpretation and understanding of astronomical data requires good
knowledge of the data acquisition process. The increase in remote observing,
queue observing, and the availability of large archived data products risk
insulating astronomers from the telescope, potentially reducing their
familiarity with the observational techniques crucial in understanding the
data. Learning fundamental observing techniques can be done in at least three
ways: 1) College and university operated observing facilities, 2) Student
involvement in national facilities through competitive proposals, 3) Programs
at national facilities to increase upper-level undergraduate and graduate
student exposure to telescopes. We encourage both national organizations and
universities to include programs and funding aimed at supporting hands-on
experience with telescopes through the three methods mentioned.Comment: "State of the Profession" white paper for the 2010 Astronomy and
Astrophysics Decadal Surve
The Importance of Nebular Continuum and Line Emission in Observations of Young Massive Star Clusters
In this spectroscopic study of infant massive star clusters, we find that
continuum emission from ionized gas rivals the stellar luminosity at optical
wavelengths. In addition, we find that nebular line emission is significant in
many commonly used broad-band HST filters including the F814W I-band, the F555W
V-band and the F435W B-band. Two young massive clusters (YMCs) in NGC 4449 were
targeted for spectroscopic observations after Reines et al. (2008a) discovered
an F814W I-band excess in their photometric study of radio-detected clusters in
the galaxy. The spectra were obtained with the Dual Imaging Spectrograph on the
3.5 m APO telescope. We supplement these data with HST and SDSS photometry. By
comparing our data to the Starburst99 and GALEV models, we find that nebular
continuum emission competes with the stellar light in our observations and that
the relative contribution is largest in the U- and I-bands, where the Balmer
and Paschen jumps are located. The spectra also exhibit strong line emission
including the [SIII] 9069,9532 lines in the HST F814W I-band. We find that the
combination of nebular continuum and line emission can account for the F814W
I-band excess found by Reines et al. (2008a). In an effort to provide a
benchmark for estimating the impact of ionized gas emission on photometric
observations of YMCs, we compute the relative contributions of the stellar
continuum, nebular continuum, and emission lines to the total flux of a 3
Myr-old cluster through various HST filter/instrument combinations, including
filters in the WFC3. We urge caution when comparing observations of YMCs to
evolutionary synthesis models since nebular emission can have a large impact on
magnitudes and colors of young (< 5 Myr) clusters, significantly affecting
inferred properties such as ages, masses and extinctions. (Abridged)Comment: 13 pages, 11 figures, Accepted for Publication in Ap
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