20 research outputs found
Microwave ISM Emission in the Green Bank Galactic Plane Survey: Evidence for Spinning Dust
We observe significant dust-correlated emission outside of H II regions in
the Green Bank Galactic Plane Survey (-4 < b < 4 degrees) at 8.35 and 14.35
GHz. The rising spectral slope rules out synchrotron and free-free emission as
majority constituents at 14 GHz, and the amplitude is at least 500 times higher
than expected thermal dust emission. When combined with the Rhodes (2.326 GHz),
and WMAP (23-94 GHz) data it is possible to fit dust-correlated emission at
2.3-94 GHz with only soft synchrotron, free-free, thermal dust, and an
additional dust-correlated component similar to Draine & Lazarian spinning
dust. The rising component generally dominates free-free and synchrotron for
\nu >~ 14 GHz and is overwhelmed by thermal dust at \nu > 60 GHz. The current
data fulfill most of the criteria laid out by Finkbeiner et al. (2002) for
detection of spinning dust.Comment: ApJ in press. 26 pages, 11 figures, figures jpeg compressed to save
spac
A Giant Sample of Giant Pulses from the Crab Pulsar
We observed the Crab pulsar with the 43-m telescope in Green Bank, WV over a
timespan of 15 months. In total we obtained 100 hours of data at 1.2 GHz and
seven hours at 330 MHz, resulting in a sample of about 95000 giant pulses
(GPs). This is the largest sample, to date, of GPs from the Crab pulsar taken
with the same telescope and backend and analyzed as one data set. We calculated
power-law fits to amplitude distributions for main pulse (MP) and interpulse
(IP) GPs, resulting in indices in the range of 2.1-3.1 for MP GPs at 1.2 GHz
and in the range of 2.5-3.0 and 2.4-3.1 for MP and IP GPs at 330 MHz. We also
correlated the GPs at 1.2 GHz with GPs from the Robert C. Byrd Green Bank
Telescope (GBT), which were obtained simultaneously at a higher frequency (8.9
GHz) over a span of 26 hours. In total, 7933 GPs from the 43-m telescope at 1.2
GHz and 39900 GPs from the GBT were recorded during these contemporaneous
observations. At 1.2 GHz, 236 (3%) MP GPs and 23 (5%) IP GPs were detected at
8.9 GHz, both with zero chance probability. Another 15 (4%) low-frequency IP
GPs were detected within one spin period of high-frequency IP GPs, with a
chance probability of 9%. This indicates that the emission processes at high
and low radio frequencies are related, despite significant pulse profile shape
differences. The 43-m GPs were also correlated with Fermi gamma-ray photons to
see if increased pair production in the magnetosphere is the mechanism
responsible for GP emission. A total of 92022 GPs and 393 gamma-ray photons
were used in this correlation analysis. No significant correlations were found
between GPs and gamma-ray photons. This indicates that increased pair
production in the magnetosphere is likely not the dominant cause of GPs.
Possible methods of GP production may be increased coherence of synchrotron
emission or changes in beaming direction.Comment: 33 pages, 10 figures, 6 tables, accepted for publication in Ap
HI Clouds in the M81 Filament as Dark Matter Minihalos--A Phase-Space Mismatch
Cosmological galaxy formation models predict the existence of dark matter
minihalos surrounding galaxies and in filaments connecting groups of galaxies.
The more massive of these minihalos are predicted to host HI gas that should be
detectable by current radio telescopes such as the GBT. We observed the region
including the M81/M82 and NGC 2403 galaxy groups, searching for observational
evidence of an HI component associated with dark matter halos within the "M81
Filament", using the Robert C. Byrd Green Bank Telescope (GBT). The map covers
an 8.7 degree x 21.3 degree (480 kpc x 1.2 Mpc) region centered between the
M81/M82 and NGC 2403 galaxy groups. Our observations cover a wide velocity
range, from -890 to 1320 km/s, which spans much of the range predicted by
cosmological N-body simulations for dark matter minihalo velocities. Our search
is not complete in the velocity range -210 to 85 km/s, containing Galactic
emission and the HVC Complex A. For an HI cloud at the distance of M81, with a
size < 10 kpc, our average 5-sigma mass detection limit is 3.2 x 10^6 M_Sun,
for a linewidth of 20 km/s. We compare our observations to two large
cosmological N-body simulations and find that the simulation predicts a
significantly greater number of detectable minihalos than are found in our
observations, and that the simulated minihalos do not match the phase space of
observed HI clouds. These results place strong constraints on the HI gas that
can be associated with dark-matter halos. Our observations indicate that the
majority of extragalactic HI clouds with a mass greater than 10^6 M_Sun are
likely to be generated through tidal stripping caused by galaxy interactions.Comment: 15 pages, 7 figures. Accepted for publication in the AJ with minor
revision
The Origin of Neutral Hydrogen Clouds in Nearby Galaxy Groups: Exploring the Range Of Galaxy Interactions
We combine high resolution N-body simulations with deep observations of
neutral hydrogen (HI) in nearby galaxy groups in order to explore two
well-known theories of HI cloud formation: HI stripping by galaxy interactions
and dark matter minihalos with embedded HI gas. This paper presents new data
from three galaxy groups, Canes Venatici I, NGC 672, and NGC 45, and assembles
data from our previous galaxy group campaign to generate a rich HI cloud
archive to compare to our simulated data.
We find no HI clouds in the Canes Venatici I, NGC 672, or NGC 45 galaxy
groups. We conclude that HI clouds in our detection space are most likely to be
generated through recent, strong galaxy interactions. We find no evidence of HI
clouds associated with dark matter halos above M_HI = 10^6 M_Sun, within +/-
700 km/s of galaxies, and within 50 kpc projected distance of galaxies.Comment: 35 pages, 10 figures, AJ accepte
Search for Diffuse Neutral Hydrogen and HI Clouds in the NGC 2403 Group
We have observed the NGC 2403 group of galaxies using the Robert C. Byrd
Green Bank Telescope (GBT) in a search for faint, extended neutral hydrogen
clouds similar to the clouds found around the M81/M82 group, which is located
approximately 250 kpc from the NGC 2403 group along the same filament of
galaxies. For an HI cloud with a size < 10 kpc within 50 kpc of a group galaxy,
our 7-sigma mass detection limit is 2.2 x 10^6 M_sun for a cloud with a
linewidth of 20 km/s, over the velocity range from -890 to 1750 km/s. At this
sensitivity level we detect 3 new HI clouds in the direction of the group, as
well as the known galaxies. The mean velocity of the new clouds differs from
that of the group galaxies by more than 250 km/s, but are in the range of Milky
Way High Velocity Clouds (HVCs) in that direction. It is most likely that the
clouds are part of the Milky Way HVC population. If HI clouds exist in the NGC
2403 group, their masses are less than 2.2 x 10^6 M_sun. We also compared our
results to structures that are expected based on recent cosmological models,
and found none of the predicted clouds. If NGC 2403 is surrounded by a
population of dark matter halos similar to those proposed for the Milky Way in
recent models, our observations imply that their HI content is less than 1% of
their total mass.Comment: Accepted by A
Neutral Hydrogen Clouds in the M81/M82 Group
We have observed a 3 degree x 3 degree area centered on the M81/M82 group of
galaxies using the Robert C. Byrd Green Bank Telescope (GBT) in a search for
analogs to the High Velocity Clouds (HVCs) of neutral hydrogen found around our
galaxy. The velocity range from -605 to -85 km/s and 25 to 1970 km/s was
searched for HI clouds. Over the inner 2 degrees x 2 degrees the 7-sigma
detection threshold was 9.6 x 10^5 M_sun. We detect 5 previously unknown HI
clouds associated with the group, as well as numerous associated filamentary HI
structures, all lying in the range -105 < V_helio < +280 km/s. From the small
angular distance of the clouds to group members, and the small velocity
difference between group members and clouds, we conclude that the clouds are
most likely relics of ongoing interactions between galaxies in the group.Comment: 17 pages, 5 figures, AJ accepte
G28.17+0.05: An unusual giant HI cloud in the inner Galaxy
New 21 cm HI observations have revealed a giant HI cloud in the Galactic
plane that has unusual properties. It is quite well defined, about 150 pc in
diameter at a distance of 5 kpc, and contains as much as 100,000 Solar Masses
of atomic hydrogen. The outer parts of the cloud appear in HI emission above
the HI background, while the central regions show HI self-absorption. Models
which reproduce the observations have a core with a temperature <40 K and an
outer envelope as much as an order of magnitude hotter. The cold core is
elongated along the Galactic plane, whereas the overall outline of the cloud is
approximately spherical. The warm and cold parts of the HI cloud have a
similar, and relatively large, line width of approximately 7 km/s. The cloud
core is a source of weak, anomalously-excited 1720 MHz OH emission, also with a
relatively large line width, which delineates the region of HI self-absorption
but is slightly blue-shifted in velocity. The intensity of the 1720 MHz OH
emission is correlated with N(H) derived from models of the cold core. There is
12CO emission associated with the cloud core. Most of the cloud mass is in
molecules, and the total mass is > 200,000 Solar Masses. In the cold core the
HI mass fraction may be 10 percent. The cloud has only a few sites of current
star formation. There may be about 100 more objects like this in the inner
Galaxy; every line of sight through the Galactic plane within 50 degrees of the
Galactic center probably intersects at least one. We suggest that G28.17+0.05
is a cloud being observed as it enters a spiral arm and that it is in the
transition from the atomic to the molecular state.Comment: 35 pages, inludes 12 figure
Radio Astronomy
Contains reports on nine research projects.National Science Foundation (Grant AST 86-17172)National Aeronautics and Space Administration (Contract NAS7-918)Jet Propulsion Laboratory (Contract 958048)U.S. Navy - Office of Naval Research (Contract N00014-84-C-2082)U.S. Navy - Office of Naval Research (Contract N00014-86-C-2114)SM Systems and Research, Inc.National Aeronautics and Space Administration/Goddard Space Flight Center (Grant NAG5-10)Center for Advanced Television StudiesBrazil, Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (Grant 300.832-82)National Aeronautics and Space Administration/Goddard Space Flight Center (Grant NAG5-537
Overview of the coordinated ground-based observations of Titan during the Huygens mission
Coordinated ground-based observations of Titan were performed around or during the Huygens atmospheric probe mission at Titan on 14 January 2005, connecting the momentary in situ observations by the probe with the synoptic coverage provided by continuing ground-based programs. These observations consisted of three different categories: (1) radio telescope tracking of the Huygens signal at 2040 MHz, (2) observations of the atmosphere and surface of Titan, and (3) attempts to observe radiation emitted during the Huygens Probe entry into Titan's atmosphere. The Probe radio signal was successfully acquired by a network of terrestrial telescopes, recovering a vertical profile of wind speed in Titan's atmosphere from 140 km altitude down to the surface. Ground-based observations brought new information on atmosphere and surface properties of the largest Satumian moon. No positive detection of phenomena associated with the Probe entry was reported. This paper reviews all these measurements and highlights the achieved results. The ground-based observations, both radio and optical, are of fundamental imnortance for the interpretatinn of results from the Huygens mission