8,015 research outputs found
EGRET Observations of the Diffuse Gamma-Ray Emission in Orion: Analysis Through Cycle 6
We present a study of the high-energy diffuse emission observed toward Orion
by the Energetic Gamma-Ray Experiment Telescope (EGRET) on the Compton
Gamma-Ray Observatory. The total exposure by EGRET in this region has increased
by more than a factor of two since a previous study. A simple model for the
diffuse emission adequately fits the data; no significant point sources are
detected in the region studied ( to and ) in either the composite dataset or in two separate
groups of EGRET viewing periods considered. The gamma-ray emissivity in Orion
is found to be for E > 100 MeV,
and the differential emissivity is well-described as a combination of
contributions from cosmic-ray electrons and protons with approximately the
local density. The molecular mass calibrating ratio is .Comment: 16 pages, including 5 figures. 3 Tables as three separate files.
Latex document, needs AASTEX style files. Accepted for publication in Ap
Giant Molecular Clouds in M33 - I. BIMA All Disk Survey
We present the first interferometric CO(J=1->0) map of the entire H-alpha
disk of M33. The 13" diameter synthesized beam corresponds to a linear
resolution of 50 pc, sufficient to distinguish individual giant molecular
clouds (GMCs). From these data we generated a catalog of 148 GMCs with an
expectation that no more than 15 of the sources are spurious. The catalog is
complete down to GMC masses of 1.5 X 10^5 M_sun and contains a total mass of
2.3 X 10^7 M_sun. Single dish observations of CO in selected fields imply that
our survey detects ~50% of the CO flux, hence that the total molecular mass of
M33 is 4.5 X 10^7 M_sun, approximately 2% of the HI mass. The GMCs in our
catalog are confined largely to the central region (R < 4 kpc). They show a
remarkable spatial and kinematic correlation with overdense HI filaments; the
geometry suggests that the formation of GMCs follows that of the filaments. The
GMCs exhibit a mass spectrum dN/dM ~ M^(-2.6 +/- 0.3), considerably steeper
than that found in the Milky Way and in the LMC. Combined with the total mass,
this steep function implies that the GMCs in M33 form with a characteristic
mass of 7 X 10^4 M_sun. More than 2/3 of the GMCs have associated HII regions,
implying that the GMCs have a short quiescent period. Our results suggest the
rapid assembly of molecular clouds from atomic gas, with prompt onset of
massive star formation.Comment: 19 pages, Accepted for Publication in the Astrophysical Journal
Supplemen
Silent messages in negotiations: The role of nonverbal communication in cross-cultural business negotiations
This study specifically explored the perceived importance of the following nonverbal factors in the negotiation process: proxemics (location and negotiation site), physical arrangement (seating and furniture arrangement), and kinesics (eye contact, facial expressions and gestures). The participants are professional business negotiators of different nationalities. The findings show that the negotiators\u27 perception about the three factors and their roles in negotiation are consistent with the nonverbal communication literature
First limits on the 3-200 keV X-ray spectrum of the quiet Sun using RHESSI
We present the first results using the Reuven Ramaty High-Energy Solar
Spectroscopic Imager, RHESSI, to observe solar X-ray emission not associated
with active regions, sunspots or flares (the quiet Sun). Using a newly
developed chopping technique (fan-beam modulation) during seven periods of
offpointing between June 2005 to October 2006, we obtained upper limits over
3-200 keV for the quietest times when the GOES12 1-8A flux fell below
Wm. These values are smaller than previous limits in the 17-120 keV
range and extend them to both lower and higher energies. The limit in 3-6 keV
is consistent with a coronal temperature MK. For quiet Sun periods
when the GOES12 1-8A background flux was between Wm and
Wm, the RHESSI 3-6 keV flux correlates to this as a power-law,
with an index of . The power-law correlation for microflares has
a steeper index of . We also discuss the possibility of
observing quiet Sun X-rays due to solar axions and use the RHESSI quiet Sun
limits to estimate the axion-to-photon coupling constant for two different
axion emission scenarios.Comment: 4 pages, 3 figures, Accepted by ApJ letter
Molecular Gas Dynamics in NGC 6946: a Bar-driven Nuclear Starburst "Caught in the Act"
We present high angular resolution ~1" and 0.6" mm-interferometric
observations of the 12CO(1-0) and 12CO(2-1) line emission in the central 300pc
of the late-type spiral galaxy NGC6946. The data, obtained with the IRAM
Plateau de Bure Interferometer (PdBI), allow the first detection of a molecular
gas spiral in the inner ~10" (270pc) with a large concentration of molecular
gas (M(H_2) ~1.6x10^7M_sun) within the inner 60pc. This nuclear clump shows
evidence for a ring-like geometry with a radius of ~10pc as inferred from the
p-v diagrams. Both the distribution of the molecular gas as well as its
kinematics can be well explained by the influence of an inner stellar bar of
about 400pc length. A qualitative model of the expected gas flow shows that
streaming motions along the leading sides of this bar are a plausible
explanation for the high nuclear gas density. Thus, NGC6946 is a prime example
of molecular gas kinematics being driven by a small-scale, secondary stellar
bar.Comment: accepted for publication in the Astrophysical Journal; 47 pages, 17
figures, 1 tabl
Diffractive Interaction and Scaling Violation in pp->pi^0 Interaction and GeV Excess in Galactic Diffuse Gamma-Ray Spectrum of EGRET
We present here a new calculation of the gamma-ray spectrum from pp->pi^0 in
the Galactic ridge environment. The calculation includes the diffractive pp
interaction and incorporates the Feynman scaling violation for the first time.
Galactic diffuse gamma-rays come, predominantly, from pi^0->gamma gamma in the
sub-GeV to multi-GeV range. Hunter et al. found, however, an excess in the GeV
range ("GeV Excess") in the EGRET Galactic diffuse spectrum above the
prediction based on experimental pp->pi^0 cross-sections and the Feynman
scaling hypothesis. We show, in this work, that the diffractive process makes
the gamma-ray spectrum harder than the incident proton spectrum by ~0.05 in
power-law index, and, that the scaling violation produces 30-80% more pi^0 than
the scaling model for incident proton energies above 100GeV. Combination of the
two can explain about a half of the "GeV Excess" with the local cosmic proton
(power-law index ~2.7). The excess can be fully explained if the proton
spectral index in the Galactic ridge is a little harder (~0.2 in power-law
index) than the local spectrum. Given also in the paper is that the diffractive
process enhances e^+ over e^- and the scaling violation gives 50-100% higher
p-bar yield than without the violation, both in the multi-GeV range.Comment: 35 pages, 11 figures, to appear in Astrophysical Journa
The Mass Function of Super Giant Molecular Complexes and Implications for Forming Young Massive Star Clusters in the Antennae (NGC 4038/39)
We have used previously published observations of the CO emission from the
Antennae (NGC 4038/39) to study the detailed properties of the super giant
molecular complexes with the goal of understanding the formation of young
massive star clusters. Over a mass range from 5E6 to 9E8 solar masses, the
molecular complexes follow a power-law mass function with a slope of -1.4 +/-
0.1, which is very similar to the slope seen at lower masses in molecular
clouds and cloud cores in the Galaxy. Compared to the spiral galaxy M51, which
has a similar surface density and total mass of molecular gas, the Antennae
contain clouds that are an order of magnitude more massive. Many of the
youngest star clusters lie in the gas-rich overlap region, where extinctions as
high as Av~100 imply that the clusters must lie in front of the gas. Combining
data on the young clusters, thermal and nonthermal radio sources, and the
molecular gas suggests that young massive clusters could have formed at a
constant rate in the Antennae over the last 160 Myr and that sufficient gas
exists to sustain this cluster formation rate well into the future. However,
this conclusion requires that a very high fraction of the massive clusters that
form initially in the Antennae do not survive as long as 100 Myr. Finally, we
compare our data with two models for massive star cluster formation and
conclude that the model where young massive star clusters form from dense cores
within the observed super giant molecular complexes is most consistent with our
current understanding of this merging system. (abbreviated)Comment: 40 pages, four figures; accepted for publication in Ap
The Origin of the Dust Arch in the Halo of NGC 4631: An Expanding Superbubble?
We study the nature and the origin of the dust arch in the halo of the
edge-on galaxy NGC 4631 detected by Neininger & Dumke (1999). We present CO
observations made using the new On-The-Fly mapping mode with the FCRAO 14m
telescope, and find no evidence for CO emission associated with the dust arch.
Our examination of previously published HI data shows that if previous
assumptions about the dust temperature and gas/dust ratio are correct, then
there must be molecular gas associated with the arch, below our detection
threshold. If this is true, then the molecular mass associated with the dust
arch is between 1.5 x 10^8 M(sun)and 9.7 x 10^8 M(sun), and likely towards the
low end of the range. A consequence of this is that the maximum allowed value
for the CO-to-H_2 conversion factor is 6.5 times the Galactic value, but most
likely closer to the Galactic value. The kinematics of the HI apparently
associated with the dust arch reveal that the gas here is not part of an
expanding shell or outflow, but is instead two separate features (a tidal arm
and a plume of HI sticking out into the halo) which are seen projected together
and appear as a shell. Thus there is no connection between the dust "arch" and
the hot X-ray emitting gas that appears to surround the galaxy Wang et al.
(2001).Comment: 14 pages, including 4 figures. Accepted by A.J. for March 200
Density Matrix Renormalization Group Study of the Spin 1/2 Heisenberg Ladder with Antiferromagnetic Legs and Ferromagnetic Rungs
The ground state and low lying excitation of the spin 1/2 Heisenberg ladder
with antiferromagnetic leg () and ferromagnetic rung () interaction is studied by means of the density matrix renormalization
group method. It is found that the state remains in the Haldane phase even for
small suggesting the continuous transition to the gapless
phase at . The critical behavior for small is studied by
the finite size scaling analysis. The result is consistent with the recent
field theoretical prediction.Comment: 11 pages, revtex, figures upon reques
Gas and Dust in the Taffy Galaxies: Ugc12914/15
We present a comprehensive study of the dust and gas properties in the
after-head-on-collision UGC12914/15 galaxy system using multi-transition CO
data and SCUBA sub-mm continuum images at both 450 and 850m. CO(3-2) line
emission was detected in the disks of UGC 12914 and UGC 12915 as well as in a
bridge connecting the two galaxies. Dust emission at 450m was detected for
the first time in the two galactic disks and in the connecting bridge. Using an
LVG excitation analysis model we have obtained good estimates of the physical
parameters in different regions of this system and the amount of molecular gas
was found to be 3-4 times lower than that estimated by other investigators
using the standard Galactic CO-to-H2 conversion factor. Comparing with the dust
mass derived from the SCUBA data, we found that the gas-to-dust ratio was
comparable to the Galactic value in the two galaxy disks but a factor of ~3
higher in the bridge. The physical condition of the molecular gas in the bridge
is comparable to that in the diffuse clouds in our Galaxy. Our result is
consistent with the scenario that the bridge molecular gas originated from the
disk molecular clouds and has been drawn out of the galactic disks due to
direct cloud-cloud collision.
Our data indicate that the global star formation efficiency (SFE) in UGC
12915 is comparable to that of normal spiral galaxies, and the SFE is 40% lower
in UGC 12914 than in UGC 12915. Little star formation activity was found in the
bridge except in an HII region adjacent to the disk of UGC 12915.Comment: Accepted by AJ. 45 pages, 10 figures (Fig 1-5 and Fig 7 in gif
format
- …