157 research outputs found
Distance Measurement of Galaxies to Redshift of 0.1 using the CO-Line Tully-Fisher Relation
We report on the first results of a long-term project to derive distances of
galaxies at cosmological distances by applying the CO-line width-luminosity
relation. We have obtained deep CO-line observations of galaxies at redshifts
up to 29,000 km/s using the Nobeyama 45-m mm-wave Telescope, and some
supplementary data were obtained by using the IRAM 30-m telescope. We have
detected the CO line emission for several galaxies, and used their CO line
widths to estimate the absolute luminosities using the line-width-luminosity
relation. In order to obtain photometric data and inclination correction, we
also performed optical imaging observations of the CO-detected galaxies using
the CFHT 3.6-m telescope at high resolution. The radio and optical data have
been combined to derive the distance moduli and distances of the galaxies, and
Hubble ratios were estimated for these galaxies. We propose that the CO line
width-luminosity relation can be a powerful method to derive distances of
galaxies to redfhift of z = 0.1 and to derive the Hubble ratio in a significant
volume of the universe.
Key words: Cosmology - Galaxies: general - Distance scale - CO lineComment: To appear in PASJ, Plain Tex, 3 figures (in 10 ps files
Comparing phenomenological recipes with a microscopic model for the electric amplitude in strangeness photoproduction
Corrections to the Born approximation in photo-induced strangeness production
off a proton are calculated in a semi-realistic microscopic model. The vertex
corrections and internal contributions to the amplitude of the reaction are included on the one-loop level. Different
gauge-invariant phenomenological prescriptions for the modification of the Born
contribution via the introduction of form factors and contact terms are
discussed. In particular, it is shown that the popular minimal-substitution
method of Ohta corresponds to a special limit of the more realistic approach.Comment: 10 pages, 6 figures in the tex
Magnetically Regulated Star Formation in 3D: The Case of Taurus Molecular Cloud Complex
We carry out three-dimensional MHD simulations of star formation in
turbulent, magnetized clouds, including ambipolar diffusion and feedback from
protostellar outflows. The calculations focus on relatively diffuse clouds
threaded by a strong magnetic field capable of resisting severe tangling by
turbulent motions and retarding global gravitational contraction in the
cross-field direction. They are motivated by observations of the Taurus
molecular cloud complex (and, to a lesser extent, Pipe Nebula), which shows an
ordered large-scale magnetic field, as well as elongated condensations that are
generally perpendicular to the large-scale field. We find that stars form in
earnest in such clouds when enough material has settled gravitationally along
the field lines that the mass-to-flux ratios of the condensations approach the
critical value. Only a small fraction (of order 1% or less) of the nearly
magnetically-critical, condensed material is turned into stars per local
free-fall time, however. The slow star formation takes place in condensations
that are moderately supersonic; it is regulated primarily by magnetic fields,
rather than turbulence. The quiescent condensations are surrounded by diffuse
halos that are much more turbulent, as observed in the Taurus complex. Strong
support for magnetic regulation of star formation in this complex comes from
the extremely slow conversion of the already condensed, relatively quiescent
CO gas into stars, at a rate two orders of magnitude below the maximum,
free-fall value. We analyze the properties of dense cores, including their mass
spectrum, which resembles the stellar initial mass function.Comment: submitted to Ap
Preserving the gauge invariance of meson production currents in the presence of explicit final-state interactions
A comprehensive formalism is developed to preserve the gauge invariance of
currents describing the photo- or electroproduction of mesons off the nucleon
when the final-state interactions of mesons and nucleons is taken into account
explicitly. Replacing exchange currents by auxiliary currents, it is found that
all contributions due to explicit final-state interactions are purely
transverse and do not contain a Kroll-Ruderman-type contact current. The
relation of the present formulation to tree-level-type prescriptions is shown.Comment: 6 pages, 2 figures; published versio
A Search for Molecular Gas in GHz Peaked Spectrum Radio Sources
We present searches for molecular gas (CO, OH, CS, and Ammonia) in six GHz
Peaked Spectrum (GPS) radio sources. We do not detect gas in any source and
place upper limits on the mass of molecular gas which are generally in the
range 1E9 to a few times 1E10 solar masses. These limits are consistent with
the following interpretations: (1) GPS sources do not require very dense gas in
their hosts, and (2) The GPS sources are unlikely to be confined by dense gas
and will evolve to become larger radio sources
Gauge-invariant theory of pion photoproduction with dressed hadrons
Based on an effective field theory of hadrons in which quantum chromodynamics
is assumed to provide the necessary bare cutoff functions, a gauge-invariant
theory of pion photoproduction with fully dressed nucleons is developed. The
formalism provides consistent dynamical descriptions of pi-N --> pi-N
scattering and Gamma-N --> pi-N production mechanisms in terms of nonlinear
integral equations for fully dressed hadrons. Defining electromagnetic currents
via the gauging of hadronic n-point Green's functions, dynamically detailed
currents for dressed nucleons are introduced. The dressed hadron currents and
the pion photoproduction current are explicitly shown to satisfy gauge
invariance in a self-consistent manner. Approximations are discussed that make
the nonlinear formalism manageable in practice and yet preserve gauge
invariance. This is achieved by recasting the gauge conditions for all
contributing interaction currents as continuity equations with ``surface''
terms for the individual particle legs coming into or going out of the hadronic
interaction region. General procedures are given that approximate any type of
(global) interaction current in a gauge-invariance preserving manner as a sum
of single-particle ``surface'' currents. It is argued that these prescriptions
carry over to other reactions, irrespective of the number or type of
contributing hadrons or hadronic systems.Comment: 33 pages, RevTeX; includes 8 postscript figures (requires psfig.sty).
This version corrects some minor errors, etc.; contains updated references.
Accepted for publication in Phys. Rev. C56 (Oct. 97
A Search for OH Megamasers at z > 0.1. III. The Complete Survey
We present the final results from the Arecibo Observatory OH megamaser
survey. We discuss in detail the properties of the remaining 18 OH megamasers
detected in the survey, including 3 redetections. We place upper limits on the
OH emission from 85 nondetections and examine the properties of 25 ambiguous
cases for which the presence or absence of OH emission could not be determined.
The complete survey has discovered 50 new OH megamasers (OHMs) in
(ultra)luminous infrared galaxies ([U]LIRGs) which doubles the sample of known
OHMs and increases the sample at z>0.1 sevenfold. The Arecibo OH megamaser
survey indicates that the OHM fraction in LIRGs is an increasing function of
the far-IR luminosity (L_{FIR}) and far-IR color, reaching a fraction of
roughly one third in the warmest ULIRGs. Significant relationships between OHMs
and their hosts are few, primarily due to a mismatch in size scales of measured
properties and an intrinsic scatter in OHM properties roughly equal to the span
of the dataset. We investigate relationships between OHMs and their hosts with
a variety of statistical tools including survival analysis, partial correlation
coefficients, and a principal component analysis. There is no apparent OH
megamaser ``fundamental plane.'' We compile data on all previously known OHMs
and evaluate the possible mechanisms and relationships responsible for OHM
production in merging systems. The OH-FIR relationship is reexamined using the
doubled OHM sample and found to be significantly flatter than previously
thought: L_{OH} ~ L_{FIR}^{1.2 +/- 0.1}. This near-linear dependence suggests a
mixture of saturated and unsaturated masers, either within individual galaxies
or across the sample.Comment: 28 pages, 14 figures, accepted by AJ. (AASTeX, includes emulateapj5
and onecolfloat5
Galaxies with unusually high abundances of molecular hydrogen
A sample of 66 galaxies from the catalog of Bettoni et al. (CISM) with
anomalously high molecular-to-atomic hydrogen mass ratios (M_{mol}/M_{HI}>2) is
considered. The sample galaxies do not differ systematically from other
galaxies in the catalog with the same morphological types, in terms of their
photometric parameters, rotational velocities, dust contents, or the total mass
of gas in comparison with galaxies of similar linear sizes and disk angular
momentum. This suggests that the overabundance of is due to transition of
HI to H_2. Galaxies with bars and active nuclei are found more frequently among
galaxies which have M_{mol} estimates in CISM. In a small fraction of galaxies,
high M_{mol}/M_{HI} ratios are caused by the overestimation of M_{mol} due to a
low conversion factor for the translation of CO-line intensities into the
number of H_2 molecules along the line of sight. It is argued that the
"molecularization" of the bulk of the gas mass could be due 1) to the
concentration of gas in the inner regions of the galactic disks, resulting to a
high gas pressure and 2) to relatively low star-formation rate per unit mass of
molecular gas which indeed takes place in galaxies with high M_{mol}/M_{HI}
ratios.Comment: 11 pages,7 figures, published in Astronomy Report
Form factors and photoproduction amplitudes
We examine the use of phenomenological form factors in tree level amplitudes
for meson photoproduction. Two common recipes are shown to be fundamentally
incorrect. An alternate form consistent with gauge invariance and crossing
symmetry is proposed.Comment: To be published in PR
1D Exciton Spectroscopy of Semiconductor Nanorods
We have theoretically shown that optical properties of semiconductor nanorods
are controlled by 1D excitons. The theory, which takes into account anisotropy
of spacial and dielectric confinement, describes size dependence of interband
optical transitions, exciton binding energies. We have demonstrated that the
fine structure of the ground exciton state explains the linear polarization of
photoluminescence. Our results are in good agreement with the measurements in
CdSe nanorods
- âŠ