1,787 research outputs found
The Detection of Anomalous Dust Emission in the Nearby Galaxy NGC 6946
We report on the Ka-band (26-40 GHz) emission properties for 10 star-forming
regions in the nearby galaxy NGC 6946. From a radio spectral decomposition, we
find that the 33 GHz flux densities are typically dominated by thermal
(free-free) radiation. However, we also detect excess Ka-band emission for an
outer-disk star-forming region relative to what is expected given existing
radio, submillimeter, and infrared data. Among the 10 targeted regions,
measurable excess emission at 33 GHz is detected for half of them, but in only
one region is the excess found to be statistically significant
(). We interpret this as the first likely detection of so
called `anomalous' dust emission outside of the Milky Way. We find that models
explaining this feature as the result of dipole emission from rapidly rotating
ultrasmall grains are able to reproduce the observations for reasonable
interstellar medium conditions. While these results suggest that the use of
Ka-band data as a measure of star formation activity in external galaxies may
be complicated by the presence of anomalous dust, it is unclear how significant
a factor this will be for globally integrated measurements as the excess
emission accounts for \la10% of the total Ka-band flux density from all 10
regions.Comment: 6 pages; Accepted to ApJ Letter
A Small Satellite as an Attached Payload on ISSâThe Merger of âSmallâ and âVery Largeâ
This paper describes the use of the Floating Potential Probe (FPP) as an âAttached Payloadâ on ISS. Background and motivation for building the FPP and well as detailed descriptions of its subsystems are described in another paper published in these proceedings (ref # SSC01-V-4b). With itâs solar arrays, primary/secondary power system, control/data processor unit, RF command/data link, thermal protection system, and two science instruments, the FPP displays most of the characteristics of a small spacecraftâ with the exception of attitude control and propulsion subsystems. The FPP was attached to the top of the P6 truss during one of several Flight 4A EVAs. It uses an RF link to communicate with an antenna (deployed at the same time as the probe) which feeds though the module and into a transmitter/receiver and portable computer inside the habitable volume. Real time data on the ISS potential is displayed on the laptop and downlinked through the ISS server when requested. This paper will provide an overview of the major subsystems, discuss how such small satellites could be made to work within the ISS system, and the possibilities of using small satellites as attached payloads for short term science or technology experiments. We will provide insight into deployment and operational considerations, show examples of the use of such a low cost system, and discuss briefly the data and science impact of this small $1M class probe
An Exploration of Partnerships Between Disability Service Units and Academic Libraries
The University of Saskatchewanâs University Library has been partnering with its institutionâs Disability Services unit for almost twenty-five years to provide space and equipment for students with disabilities in some of its library locations. This partnership has grown from piloting a Kurzweil reader, to the development of multiple assistive technology and exam writing rooms, to the recent creation of a multi-purpose room. These library spaces complement spaces Disability Services has within its own office suite and reflect the growth in the number of students registered with them, a widening spectrum of disabilities, and a collaborative desire to make disability services and resources more accessible. A literature scan revealed a small number of articles about partnerships, many of which were in response to legislation. A survey directed at North American post-secondary institutionsâ Disability Services employees surfaced further information about partnerships, but did not reveal any common best practices. With the increase in the number of students with disabilities attending academic institutions and a changing landscape of what is defined as a disability, how and how well academic libraries and Disability Services units are partnering to respond to these changes appears to require further exploration and assessment
Environmental Effects in Clusters: Modified Far-Infrared--Radio Relations within Virgo Cluster Galaxies
(abridged) We present a study on the effects of the intracluster medium (ICM)
on the interstellar medium (ISM) of 10 Virgo cluster spiral galaxies using {\it
Spitzer} far-infrared (FIR) and VLA radio continuum imaging. Relying on the
FIR-radio correlation within normal galaxies, we use our infrared data to
create model radio maps which we compare to the observed radio images. For 6 of
our sample galaxies we find regions along their outer edges that are highly
deficient in the radio compared with our models. We believe these observations
are the signatures of ICM ram pressure. For NGC 4522 we find the radio deficit
region to lie just exterior to a region of high radio polarization and flat
radio spectral index, although the total 20 cm radio continuum in this region
does not appear strongly enhanced. These characteristics seem consistent for
other galaxies with radio polarization data in the literature. The strength of
the radio deficit is inversely correlated with the time since peak pressure as
inferred from stellar population studies and gas stripping simulations,
suggesting the strength of the radio deficit is good indicator of the strength
of the current ram pressure. We also find that galaxies having {\it local}
radio {\it deficits} appear to have {\it enhanced global} radio fluxes. Our
preferred physical picture is that the observed radio deficit regions arise
from the ICM wind sweeping away cosmic-ray (CR) electrons and the associated
magnetic field, thereby creating synchrotron tails as observed for some of our
galaxies. We propose that CR particles are also re-accelerated by ICM-driven
shocklets behind the observed radio deficit regions which in turn enhances the
remaining radio disk brightness.Comment: 19 pages, 10 figures; Astrophysical Journa
Little Drummer Bot: Building, Testing, and Interfacing With a New Expressive Mechatronic Drum System
(Abstract to follow
An Accounting of the Dust-Obscured Star Formation and Accretion Histories Over the Last ~11~Billion Years
(Abridged) We report on an accounting of the star formation and accretion
driven energetics of 24um detected sources in GOODS North. For sources having
infrared (IR; 8-1000um) luminosities >3x10^12 L_sun when derived by fitting
local SEDs to 24um photometry alone, we find these IR luminosity estimates to
be a factor of ~4 times larger than those estimated when the SED fitting
includes additional 16 and 70um data (and in some cases mid-infrared
spectroscopy and 850um data). This discrepancy arises from the fact that high
luminosity sources at z>>0 appear to have far- to mid-infrared ratios, as well
as aromatic feature equivalent widths, typical of lower luminosity galaxies in
the local Universe. Using our improved estimates for IR luminosity and AGN
contributions, we investigate the evolution of the IR luminosity density versus
redshift arising from star formation and AGN processes alone. We find that,
within the uncertainties, the total star formation driven IR luminosity density
is constant between 1.15 < z < 2.35, although our results suggest a slightly
larger value at z>2. AGN appear to account for <18% of the total IR luminosity
density integrated between 0< z < 2.35, contributing <25% at each epoch. LIRG
appear to dominate the star formation rate (SFR) density along with normal
star-forming galaxies (L_IR < 10^11 L_sun) between 0.6 < z < 1.15. Once beyond
z >2, the contribution from ultraluminous infrared galaxies ULIRGs becomes
comparable with that of LIRGs. Using our improved IR luminosity estimates, we
find existing calibrations for UV extinction corrections based on measurements
of the UV spectral slope typically overcorrect UV luminosities by a factor of
~2, on average, for our sample of 24um-selected sources; accordingly we have
derived a new UV extinction correction more appropriate for our sample.Comment: Accepted for publication in Ap
Characterizing Cosmic-Ray Propagation in Massive Star-forming Regions: The Case of 30 Doradus and the Large Magellanic Cloud
Using infrared, radio, and Îł-ray data, we investigate the propagation characteristics of cosmic-ray (CR) electrons and nuclei in the 30 Doradus (30 Dor) star-forming region in the Large Magellanic Cloud (LMC) using a phenomenological model based on the radio-far-infrared correlation within galaxies. Employing a correlation analysis, we derive an average propagation length of ~100-140 pc for ~3 GeV CR electrons resident in 30 Dor from consideration of the radio and infrared data. Assuming that the observed Îł-ray emission toward 30 Dor is associated with the star-forming region, and applying the same methodology to the infrared and Îł-ray data, we estimate a ~20 GeV propagation length of 200-320 pc for the CR nuclei. This is approximately twice as large as for ~3 GeV CR electrons, corresponding to a spatial diffusion coefficient that is ~4 times higher, scaling as (R/GV)δ with δ â 0.7-0.8 depending on the smearing kernel used in the correlation analysis. This value is in agreement with the results found by extending the correlation analysis to include ~70 GeV CR nuclei traced by the 3-10 GeV Îł-ray data (δ â 0.66 Âą 0.23). Using the mean age of the stellar populations in 30 Dor and the results from our correlation analysis, we estimate a diffusion coefficient D_R â (0.9-1.0) Ă 10^(27)(R/GV)0.7 cm^(2) s^(â1). We compare the values of the CR electron propagation length and surface brightness for 30 Dor and the LMC as a whole with those of entire disk galaxies. We find that the trend of decreasing average CR propagation distance with increasing disk-averaged star formation activity holds for the LMC, and extends down to single star-forming regions, at least for the case of 30 Dor
An upper-limit on the linear polarization fraction of the GW170817 radio continuum
We present late-time radio observations of GW170817, the first binary neutron
star merger discovered through gravitational waves by the advanced LIGO and
Virgo detectors. Our observations, carried out with the Karl G. Jansky Very
Large Array, were optimized to detect polarized radio emission, and thus to
constrain the linear polarization fraction of GW170817. At an epoch of ~244
days after the merger, we rule out linearly polarized emission above a fraction
of ~12% at a frequency of 2.8 GHz (99% confidence). Within the structured jet
scenario (a.k.a. successful jet plus cocoon system) for GW170817, the derived
upper-limit on the radio continuum linear polarization fraction strongly
constrains the magnetic field configuration in the shocked ejecta. We show that
our results for GW170817 are compatible with the low level of linear
polarization found in afterglows of cosmological long gamma-ray bursts.
Finally, we discuss our findings in the context of future expectations for the
study of radio counterparts of binary neutron star mergers identified by
ground-based gravitational-wave detectors.Comment: 5 pages, 2 figures, 1 tabl
APM 08279+5255: Keck Near- and Mid-IR High-Resolution Imaging
We present Keck high-resolution near-IR (2.2 microns; FWHM~0.15") and mid-IR
(12.5 microns; FWHM~0.4") images of APM08279+5255, a z=3.91 IR-luminous BALQSO
with a prodigious apparent bolometric luminosity of 5x10^{15} Lsun, the largest
known in the universe. The K-band image shows that this system consists of
three components, all of which are likely to be the gravitationally lensed
images of the same background object, and the 12.5 micron image shows a
morphology consistent with such an image configuration. Our lens model suggests
that the magnification factor is ~100 from the restframe UV to mid-IR, where
most of the luminosity is released. The intrinsic bolometric luminosity and IR
luminosity of APM08279+5255 are estimated to be 5x10^{13} Lsun and 1x10^{13}
Lsun, respectively. This indicates that APM 08279+5255 is intriniscally
luminous, but it is not the most luminous object known. As for its dust
contents, little can be determined with the currently available data due to the
uncertainties associated with the dust emissivity and the possible effects of
differential magnification. We also suggest that the lensing galaxy is likely
to be a massive galaxy at z~3.Comment: 32 pages, 4 tables, 11 figures; Accepted for publication in Ap
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