3,369 research outputs found
Radio continuum and far-infrared emission from the galaxies in the Eridanus group
The Eridanus galaxies follow the well-known radio-FIR correlation. Majority
(70%) of these galaxies have their star formation rates below that of the Milky
Way. The galaxies having a significant excess of radio emission are identified
as low luminosity AGNs based on their radio morphologies obtained from the GMRT
observations. There are no powerful AGNs (L{20cm} > 10^{23} W Hz^{-1}) in the
group. The two most far-infrared and radio luminous galaxies in the group have
optical and HI morphologies suggestive of recent tidal interactions. The
Eridanus group also has two far-infrared luminous but radio-deficient galaxies.
It is believed that these galaxies are observed within a few Myr of the onset
of an intense star formation episode after being quiescent for at least a 100
Myr. The upper end of the radio luminosity distribution of the Eridanus
galaxies (L_{20cm} ~ 10^{22} W Hz^{-1}) is consistent with that of the field
galaxies, other groups, and late-type galaxies in nearby clusters.Comment: 16 pages; Accepted for publication in Journal of Astroph. & Astron.
March, 200
Dynamics of Electrons in Graded Semiconductors
I present a theory of electron dynamics in semiconductors with slowly varying
composition. I show that the frequency-dependent conductivity, required for the
description of transport and optical properties, can be obtained from a
knowledge of the band structures and momentum matrix elements of homogeneous
semiconductor alloys. New sum rules for the electronic oscillator strengths,
which apply within a given energy band or between any two bands, are derived,
and a general expression for the width of the intraband absorption peak is
given. Finally, the low-frequency dynamics is discussed, and a correspondence
with the semiclassical motion is established.Comment: 4 pages, Revte
Quasars in the MAMBO blank field survey
Our MAMBO 1.2 mm blank field imaging survey of ~0.75 sqd has uncovered four
unusually bright sources, with flux densities between 10 and 90 mJy, all
located in the Abell 2125 field. The three brightest are flat spectrum radio
sources with bright optical and X-ray counterparts. Their mm and radio flux
densities are variable on timescales of months. Their X-ray luminosities
classify them as quasars. The faintest of the four mm bright sources appears to
be a bright, radio-quiet starburst at z~3, similar to the sources seen at lower
flux densities in the MAMBO and SCUBA surveys. It may also host a mildly
obscured AGN of quasar-like X-ray luminosity. The three non-thermal mm sources
imply an areal density of flat spectrum radio sources higher by at least 7
compared with that expected from an extrapolation of the lower frequency radio
number counts.Comment: 8 pages, 7 figures. Accepted for publication by A&
Alternative Mathematical Technique to Determine LS Spectral Terms
We presented an alternative computational method for determining the
permitted LS spectral terms arising from electronic configurations. This
method makes the direct calculation of LS terms possible. Using only basic
algebra, we derived our theory from LS-coupling scheme and Pauli exclusion
principle. As an application, we have performed the most complete set of
calculations to date of the spectral terms arising from electronic
configurations, and the representative results were shown. As another
application on deducing LS-coupling rules, for two equivalent electrons, we
deduced the famous Even Rule; for three equivalent electrons, we derived a new
simple rule.Comment: Submitted to Phys. Rev.
The Megamaser Cosmology Project. III. Accurate Masses of Seven Supermassive Black Holes in Active Galaxies with Circumnuclear Megamaser Disks
Observations of HO masers from circumnuclear disks in active galaxies for
the Megamaser Cosmology Project allow accurate measurement of the mass of
supermassive black holes (BH) in these galaxies. We present the Very Long
Baseline Interferometry (VLBI) images and kinematics of water maser emission in
six active galaxies: NGC~1194, NGC~2273, NGC~2960 (Mrk~1419), NGC~4388,
NGC~6264 and NGC~6323. We use the Keplerian rotation curves of these six
megamaser galaxies, plus a seventh previously published, to determine accurate
enclosed masses within the central pc of these galaxies, smaller than
the radius of the sphere of influence of the central mass in all cases. We also
set lower limits to the central mass densities of between 0.12 and 60 ~pc. For six of the seven disks, the high central
densities rule out clusters of stars or stellar remnants as the central
objects, and this result further supports our assumption that the enclosed mass
can be attributed predominantly to a supermassive black hole. The seven BHs
have masses ranging between 0.76 and 6.510. The BH mass
errors are \%, dominated by the uncertainty of the Hubble constant.
We compare the megamaser BH mass determination with other BH mass measurement
techniques. The BH mass based on virial estimation in four galaxies is
consistent with the megamaser BH mass given the latest empirical value of
, but the virial mass uncertainty is much greater. MCP
observations continue and we expect to obtain more maser BH masses in the
future.Comment: 18 pages, 4 figures. This paper has been submitted to ApJ. An updated
version of this paper will be posted when it gets accepte
Incidence of Extended-Spectrum-beta-Lactamase-Producing Escherichia coli and Klebsiella pneumoniae Isolates That Test Susceptible to Cephalosporins and Aztreonam by the Revised CLSI Breakpoints
The incidence of aztreonam and cephalosporin susceptibility, determined using the revised CLSI breakpoints, for extendedspectrum-beta-lactamase (ESBL)-producing Escherichia coli and Klebsiella pneumoniae isolates was evaluated. Our analysis showed that results for aztreonam and/or\u3e 1 cephalosporin were reported as susceptible or intermediate for 89.2% of ESBLproducing E coli isolates (569/638 isolates) and 67.7% of ESBL-producing K. pneumoniae isolates (155/229 isolates)
Cosmology and the Hubble Constant: On the Megamaser Cosmology Project (MCP)
The Hubble constant Ho describes not only the expansion of local space at
redshift z ~ 0, but is also a fundamental parameter determining the evolution
of the universe. Recent measurements of Ho anchored on Cepheid observations
have reached a precision of several percent. However, this problem is so
important that confirmation from several methods is needed to better constrain
Ho and, with it, dark energy and the curvature of space. A particularly direct
method involves the determination of distances to local galaxies far enough to
be part of the Hubble flow through water vapor (H2O) masers orbiting nuclear
supermassive black holes. The goal of this article is to describe the relevance
of Ho with respect to fundamental cosmological questions and to summarize
recent progress of the the `Megamaser Cosmology Project' (MCP) related to the
Hubble constant.Comment: 10 pages, 7 postscript figures (8 ps files), IAU Symposium 287, uses
iaus.cl
Asymptotic solvers for ordinary differential equations with multiple frequencies
We construct asymptotic expansions for ordinary differential equations with highly oscillatory forcing terms, focusing on the case of multiple, non-commensurate frequencies. We derive an asymptotic expansion in inverse powers of the oscillatory parameter and use its truncation as an exceedingly effective means to discretize the differential equation in question. Numerical examples illustrate the effectiveness of the method
Radio continuum of galaxies with HO megamaser disks: 33 GHz VLA data
We investigate the nuclear environment of galaxies with observed 22 GHz water
megamaser in their subparsec edge-on accretion disks, using 33 GHz (9mm) radio
continuum data from VLA, with a resolution of ~ 0.2-0.5 arcsecs, and relate the
maser and host galaxy properties to those of its radio continuum emission.
Eighty-seven percent (21 out of 24) galaxies in our sample show 33 GHz radio
continuum emission at levels of 4.5-240 . Five sources show extended
emission, including one source with two main components and one with three main
components. The remaining detected 16 sources exhibit compact cores within the
sensitivity limits. Little evidence is found for extended jets (>300 pc) in
most sources. Either they do not exist, or our chosen frequency of 33 GHz is
too high for a detection of these supposedly steep spectrum features. In only
one source among those with known maser disk orientation, NGC4388, we found an
extended jet-like feature that appears to be oriented perpendicular to the
water megamaser disk. Smaller 100-300 pc sized jets might also be present, as
is suggested by the beam-deconvolved morphology of our sources. Whenever
possible, central positions with accuracies of 20-280 mas are provided. A
correlation analysis shows that the 33 GHz luminosity weakly correlates with
the infrared luminosity. The 33 GHz luminosity is anticorrelated with the
circular velocity of the galaxy. The black hole masses show stronger
correlations with water maser luminosity than with 1.4 GHz, 33 GHz, or hard
X-ray luminosities. Furthermore, the inner radii of the disks show stronger
correlations with 1.4 GHz, 33 GHz, and hard X-ray luminosities than their outer
radii, suggesting that the outer radii may be affected by disk warping, star
formation, or peculiar density distributions.Comment: 18 pages, 10 figures, Accepted for publication in A&
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