1,436 research outputs found
PC1643+4631A,B: The Lyman-Alpha Forest at the Edge of Coherence
This is the first measurement and detection of coherence in the intergalactic
medium (IGM) at substantially high redshift (z~3.8) and on large physical
scales (~2.5 h^-1 Mpc). We perform the measurement by presenting new
observations from Keck LRIS of the high redshift quasar pair PC 1643+4631A, B
and their Ly-alpha absorber coincidences. This experiment extends multiple
sightline quasar absorber studies to higher redshift, higher opacity, larger
transverse separation, and into a regime where coherence across the IGM becomes
weak and difficult to detect. We fit 222 discrete Ly-alpha absorbers to
sightline A and 211 to sightline B. Relative to a Monte Carlo pairing test
(using symmetric, nearest neighbor matching) the data exhibit a 4sigma excess
of pairs at low velocity splitting (<150 km/s), thus detecting coherence on
transverse scales of ~2.5 h^-1 Mpc. We use spectra extracted from an SPH
simulation to analyze symmetric pair matching, transmission distributions as a
function of redshift and compute zero-lag cross-correlations to compare with
the quasar pair data. The simulations agree with the data with the same
strength (~4sigma) at similarly low velocity splitting above random chance
pairings. In cross-correlation tests, the simulations agree when the mean flux
(as a function of redshift) is assumed to follow the prescription given by
Kirkman et al. (2005). While the detection of flux correlation (measured
through coincident absorbers and cross-correlation amplitude) is only
marginally significant, the agreement between data and simulations is
encouraging for future work in which even better quality data will provide the
best insight into the overarching structure of the IGM and its understanding as
shown by SPH simulations.Comment: 15 pages, 11 figures; accepted for publication in Astronomical
Journa
Comparing Simulations and Observations of the Lyman-Alpha Forest I. Methodology
We describe techniques for comparing spectra extracted from cosmological
simulations and observational data, using the same methodology to link
Lyman-alpha properties derived from the simulations with properties derived
from observational data. The eventual goal is to measure the coherence or
clustering properties of Lyman-alpha absorbers using observations of quasar
pairs and groups. We quantify the systematic underestimate in opacity that is
inherent in the continuum fitting process of observed spectra over a range of
resolution and signal-to-noise ratio. We present an automated process for
detecting and selecting absorption features over the range of resolution and
signal-to-noise of typical observational data on the Lyman-alpha "forest".
Using these techniques, we detect coherence over transverse scales out to 500
h^{-1}_{50} kpc in spectra extracted from a cosmological simulation at z = 2.Comment: 52 pages, includes 14 figures, to appear in ApJ v566 Feb 200
Ocean feature recognition using genetic algorithms with fuzzy fitness functions (GA/F3)
A model for genetic algorithms with semantic nets is derived for which the relationships between concepts is depicted as a semantic net. An organism represents the manner in which objects in a scene are attached to concepts in the net. Predicates between object pairs are continuous valued truth functions in the form of an inverse exponential function (e sub beta lxl). 1:n relationships are combined via the fuzzy OR (Max (...)). Finally, predicates between pairs of concepts are resolved by taking the average of the combined predicate values of the objects attached to the concept at the tail of the arc representing the predicate in the semantic net. The method is illustrated by applying it to the identification of oceanic features in the North Atlantic
Quasars as Absorption Probes of the J0053+1234 Region
We present UBRI photometry and spectra for 60 quasars found within one square
degree centered on the J0053+1234 region, which has been the subject of the
Caltech Faint Galaxy Redshift Survey. Candidate quasars were selected by their
ultraviolet excess with respect to the stellar locus, and confirmed
spectroscopically. The quasars span a wide range in brightness (17.5<B<21.6)
and redshift (0.43<z<2.38). These new quasars comprise a grid of absorption
probes that can be used to study large-scale structure as well as the
correlation between luminous galaxies, non-luminous halos, and Lyman-alpha
absorbers in the direction of the deep pencil-beam galaxy survey. Spectra of 14
emission line galaxies found using the same technique are also presented.Comment: Accepted for publication in the Astronomical Journal; 29 pages,
including 6 tables and 7 figure
Investigation for high-impact SNPs on important genes for muscle growth characteristics in broilers.
A Study of Lyman-Alpha Quasar Absorbers in the Nearby Universe
Spectroscopy of ten quasars obtained with the Goddard High Resolution
Spectrograph (GHRS) of the Hubble Space Telescope (HST) is presented. A
clustering analysis reveals an excess of nearest neighbor line pairs on
velocity scales of 250-750 km/s at a 95-98% confidence level. The hypothesis
that the absorbers are randomly distributed in velocity space can be ruled out
at the 99.8% confidence level. No two-point correlation power is detected (xi <
1 with 95% confidence). Lyman-alpha absorbers have correlation amplitudes on
scales of 250-500 km/s at least 4-5 times smaller than the correlation
amplitude of bright galaxies. A detailed comparison between absorbers in nearby
galaxies is carried out on a limited subset of 11 Lyman- alpha absorbers where
the galaxy sample in a large contiguous volume is complete to M_B = -16.
Absorbers lie preferentially in regions of intermediate galaxy density but it
is often not possible to uniquely assign a galaxy counterpart to an absorber.
This sample provides no explicit support for the hypothesis that absorbers are
preferentially associated with the halos of luminous galaxies. We have made a
preliminary comparison of the absorption line properties and environments with
the results of hydrodynamic simulations. The results suggest that the
Lyman-alpha absorbers represent diffuse or shocked gas in the IGM that traces
the cosmic web of large scale structure. (abridged)Comment: 36 pages of text, 15 figures, 4 tables, 36 file
A search for signatures of interactions of X-ray binary outflows with their environments with ALMA
We observed the X-ray binaries CirX-1, ScoX-1, GRS 1915+105, GX13+1, and
CygX-1 with the Atacama Large Millimeter/submillimeter Array (ALMA). Unresolved
continuum emission is found at the positions of all the sources at a frequency
of 92 GHz, with flux densities ranging between 0.8 and 10 mJy/beam. In all
cases the emission can be associated with jets that have been extensively
observed at lower frequencies. We searched for line emission from H
recombination, SiO,H2O, and CH3OH at the positions of all the sources and, for
CirX-1 and CygX-1, also at regions where shocks associated with an interaction
between the jet and the interstellar medium had previously been observed. The
search did not yield any significant detection, resulting in 3 upper
limits between 0.65 and 3.7 K km s for the existence of line emission in
these regions. In contrast, we detected spatially unresolved SiO emission in
the field of view of GX13+1, and we tentatively associate this emission with a
SiO maser in a potential young stellar object or evolved star. We also found
spatially extended line emission at two additional sites in the field of view
of GX13+1 that we tentatively associate with emission from SO and CH3OH; we
speculate that it may be associated with a star-forming region, but again we
cannot rule out alternative origins such as emission from evolved stars.Comment: Accepted for publication in A&
Electromagnetic Meson Form Factors in the Salpeter Model
We present a covariant scheme to calculate mesonic transitions in the
framework of the Salpeter equation for -states. The full Bethe
Salpeter amplitudes are reconstructed from equal time amplitudes which were
obtained in a previous paper\cite{Mue} by solving the Salpeter equation for a
confining plus an instanton induced interaction. This method is applied to
calculate electromagnetic form factors and decay widths of low lying
pseudoscalar and vector mesons including predictions for CEBAF experiments. We
also describe the momentum transfer dependence for the processes
.Comment: 22 pages including 10 figure
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