3,704 research outputs found
The Caltech Faint Galaxy Redshift Survey XII: Clustering of Galaxies
A clustering analysis is performed on two samples of faint
galaxies each, in two widely separated regions of the sky, including the Hubble
Deep Field. One of the survey regions is configured so that some galaxy pairs
span angular separations of up to 1 deg. The median redshift is . Strong clustering is obvious, with every pencil-beam field containing a
handful of narrow redshift-space features, corresponding to galaxy structures
with sizes of 5 to 20 Mpc. The structures are not obviously organized on
planes, though one prominent, colinear triplet of structures is observed,
spanning Mpc. This may be evidence of a filament. A galaxy--galaxy
correlation function calculation is performed. No significant evolution of
clustering (relative to stable clustering) is found in the redshift range
0.3<z<1.0. This is not surprising, since uncertainties in the correlation
amplitude estimated from surveys like these are large; field-to-field
variations and covariances between data points are both shown to be
significant. Consistent with other studies in this redshift range, the
galaxy--galaxy correlation length is found to be somewhat smaller than that
predicted from local measurements and an assumption of no evolution. Galaxies
with absorption-line-dominated spectra show much stronger clustering at
distances of <2 Mpc than typical field galaxies. There is some evidence for
weaker clustering at intermediate redshift than at low redshift, when the
results presented here are compared with surveys of the local Universe. In
subsets of the data, the measured pairwise velocity dispersion of galaxies
ranges from 200 to , depending on the properties of the dominant
redshift structures in each subset.Comment: accepted for publication in the Ap
On the Expressivity and Applicability of Model Representation Formalisms
A number of first-order calculi employ an explicit model representation
formalism for automated reasoning and for detecting satisfiability. Many of
these formalisms can represent infinite Herbrand models. The first-order
fragment of monadic, shallow, linear, Horn (MSLH) clauses, is such a formalism
used in the approximation refinement calculus. Our first result is a finite
model property for MSLH clause sets. Therefore, MSLH clause sets cannot
represent models of clause sets with inherently infinite models. Through a
translation to tree automata, we further show that this limitation also applies
to the linear fragments of implicit generalizations, which is the formalism
used in the model-evolution calculus, to atoms with disequality constraints,
the formalisms used in the non-redundant clause learning calculus (NRCL), and
to atoms with membership constraints, a formalism used for example in decision
procedures for algebraic data types. Although these formalisms cannot represent
models of clause sets with inherently infinite models, through an additional
approximation step they can. This is our second main result. For clause sets
including the definition of an equivalence relation with the help of an
additional, novel approximation, called reflexive relation splitting, the
approximation refinement calculus can automatically show satisfiability through
the MSLH clause set formalism.Comment: 15 page
The Fourth BATSE Gamma-Ray Burst Catalog (Revised)
The Burst and Transient Source Experiment (BATSE) on the Compton Gamma Ray
Observatory (CGRO) has triggered on 1637 cosmic gamma-ray bursts between 1991
April 19 and 1996 August 29. These events constitute the Fourth BATSE burst
catalog. The current version (4Br) has been revised from the version first
circulated on CD-ROM in September 1997 (4B) to include improved locations for a
subset of bursts that have been reprocssed using additional data. A significant
difference from previous BATSE catalogs is the inclusion of bursts from periods
when the trigger energy range differed from the nominal 50-300 keV. We present
tables of the burst occurrence times, locations, peak fluxes, fluences, and
durations. In general, results from previous BATSE catalogs are confirmed here
with greater statistical significance.Comment: 45 pages, 12 Postscript figures, accepted for publication in Ap. J.
Supp
The non-Gaussian tail of cosmic-shear statistics
Due to gravitational instability, an initially Gaussian density field
develops non-Gaussian features as the Universe evolves. The most prominent
non-Gaussian features are massive haloes, visible as clusters of galaxies. The
distortion of high-redshift galaxy images due to the tidal gravitational field
of the large-scale matter distribution, called cosmic shear, can be used to
investigate the statistical properties of the LSS. In particular, non-Gaussian
properties of the LSS will lead to a non-Gaussian distribution of cosmic-shear
statistics. The aperture mass () statistics, recently introduced as
a measure for cosmic shear, is particularly well suited for measuring these
non-Gaussian properties. In this paper we calculate the highly non-Gaussian
tail of the aperture mass probability distribution, assuming Press-Schechter
theory for the halo abundance and the `universal' density profile of haloes as
obtained from numerical simulations. We find that for values of
much larger than its dispersion, this probability distribution is closely
approximated by an exponential, rather than a Gaussian. We determine the
amplitude and shape of this exponential for various cosmological models and
aperture sizes, and show that wide-field imaging surveys can be used to
distinguish between some of the currently most popular cosmogonies. Our study
here is complementary to earlier cosmic-shear investigations which focussed
more on two-point statistical properties.Comment: 9 pages, 5 figures, submitted to MNRA
The Opacity of Nearby Galaxies from Counts of Background Galaxies: II. Limits of the Synthetic Field Method
Recently, we have developed and calibrated the Synthetic Field Method (SFM)
to derive the total extinction through disk galaxies. The method is based on
the number counts and colors of distant background field galaxies that can be
seen through the foreground object, and has been successfully applied to NGC
4536 and NGC 3664, two late-type galaxies located, respectively, at 16 and 11
Mpc. Here, we study the applicability of the SFM to HST images of galaxies in
the Local Group, and show that background galaxies cannot be easily identified
through these nearby objects, even with the best resolution available today. In
the case of M 31, each pixel in the HST images contains 50 to 100 stars, and
the background galaxies cannot be seen because of the intrinsic granularity due
to strong surface brightness fluctuations. In the LMC, on the other hand, there
is only about one star every six linear pixels, and the lack of detectable
background galaxies results from a ``secondary'' granularity, introduced by
structure in the wings of the point spread function. The success of the SFM in
NGC 4536 and NGC 3664 is a natural consequence of the reduction of the
intensity of surface brightness fluctuations with distance. When the dominant
confusion factor is structure in the PSF wings, as is the case of HST images of
the LMC, and would happen in M 31 images obtained with a 10-m diffraction-
limited optical telescope, it becomes in principle possible to improve the
detectability of background galaxies by subtracting the stars in the foreground
object. However, a much better characterization of optical PSFs than is
currently available would be required for an adequate subtraction of the wings.
Given the importance of determining the dust content of Local Group galaxies,
efforts should be made in that direction.Comment: 45 pages, 10 Postscript figure
Galaxy Clustering Evolution in the UH8K Weak Lensing Fields
We present measurements of the two-point galaxy angular correlation function
as a function of apparent magnitude, color, and morphology. We present new
galaxy number counts to limiting magnitudes of I=24.0 and V=25.0. We find
to be well described by a power-law of slope -0.8. We find the
amplitude of the correlation function to decrease monotonically with
increasingly faint apparent magnitude. We compare with predictions utilizing
redshift distributions based on deep spectroscopic observations. We conclude
that simple redshift-dependent models which characterize evolution by means of
the epsilon parameter inadequately describe the observations. We find a strong
clustering dependence on V-I color because galaxies of extreme color lie at
similar redshifts and the angular correlation functions for these samples are
minimally diluted by chance projections.
We then present the first attempt to investigate the redshift evolution of
clustering, utilizing a population of galaxies of the same morphological type
and absolute luminosity. We study the dependence of on
redshift for Lstar early-type galaxies in the redshift range 0.2<z<0.9.
Although uncertainties are large, we find the evolution in the clustering of
these galaxies to be consistent with stable clustering [epsilon=0]. We find
Lstar early-type galaxies to cluster slightly more strongly (rnought =
5.25\pm0.28 \hMpc assuming epsilon=0) than the local full field population.
This is in good agreement with the 2dFGRS value for Lstar early-type galaxies
in the local universe (abridged).Comment: 41 pages, including 12 figs, 10 tables, to appear in Ap
Unstable states in QED of strong magnetic fields
We question the use of stable asymptotic scattering states in QED of strong
magnetic fields. To correctly describe excited Landau states and photons above
the pair creation threshold the asymptotic fields are chosen as generalized
Licht fields. In this way the off-shell behavior of unstable particles is
automatically taken into account, and the resonant divergences that occur in
scattering cross sections in the presence of a strong external magnetic field
are avoided. While in a limiting case the conventional electron propagator with
Breit-Wigner form is obtained, in this formalism it is also possible to
calculate -matrix elements with external unstable particles.Comment: Revtex, 7 pages. To appear in Phys. Rev. D53(2
The Angular Clustering of Lyman-Break Galaxies at Redshift z=3
We have measured the angular correlation function w(theta) for a sample of
871 Lyman-break galaxies (LBGs) at z=3. Fitting a power-law to a weighted
average of w(theta) from 5 fields, we find the amplitude to be A_w=2
arcsec^{\beta} and the slope \beta=0.9. The slope is the same as in the local
and moderate redshift universe. A slope \beta=0.25 or shallower is ruled out by
the data at the 99.9% confidence level. Because N(z) of LBGs is well determined
from 376 spectroscopic redshifts, the real-space correlation function can be
derived from the angular one through the Limber transform. This inversion is
rather insensitive to the still relatively large errors on A_w and \beta, and
the spatial correlation length is much more tightly constrained than either of
these parameters. We estimate r_0=3.3 -0.6 +0.7 (2.1 -0.5 +0.4) h^{-1} Mpc
(comoving) for q_0=0.1 (0.5) at z=3.04 (h is in units of 100 km/s/Mpc). The
correlation length of LBGs at z=3 is comparable to that of present-day spiral
galaxies and is only about 50% smaller than that of the ellipticals; it is as
large or larger than any measured in galaxy samples at 0.3<z<1. By comparing
the observed galaxy correlation length to that of the mass predicted from CDM
theory, we estimate a bias for LBGs of b\sim 1.5 (4.5) for q_0=0.1 (0.5), in
agreement with our previous estimates based on preliminary spectroscopy. The
strong clustering and the large bias of the LBGs are consistent with biased
galaxy formation theories and provide additional evidence that these systems
are associated with massive dark matter halos. The clustering of LBGs at z=3
emphasizes that apparent evolution of galaxy clustering may be due as much to
variations in effective bias parameter among different samples as to evolution
in the mass distribution through gravitational instability.Comment: 24 pages, 4 postscript figures, LaTex, uses aaspp4.sty, to be
published in The Astrophysical Journa
A Large Structure of Galaxies At Redshift z~3 and its Cosmological Implications
We report the discovery of a highly significant concentration of galaxies at
a redshift of =3.090. The structure is evident in a redshift histogram of
photometrically selected ``Lyman break'' objects in a 9' by 18' field in which
we have obtained 78 spectroscopic redshifts in the range 2.0 < z <3.4. The
dimensions of the structure projected on the plane of the sky are at least
11'by 8', or 14h_{70}^{-1} by 10h_{70}^{-1} Mpc (comoving; \Omega_M=1). The
concentration contains 15 galaxies and one faint (R=21.7) QSO. We consider the
structure in the context of a number of cosmological models and argue that
Lyman-break galaxies must be very biased tracers of mass, with an effective
bias on mass scale M~10^{15}M_{\sun} ranging from b~2 for \Omega_M=0.2 to b >~6
for \Omega_M=1. In a Cold Dark Matter scenario the large bias values suggest
that individual Lyman-break galaxies are associated with dark halos of mass
M~10^{12} M_{\sun}, reinforcing the interpretation of these objects as the
progenitors of massive galaxies at the present epoch. Preliminary results of
spectroscopy in additional fields suggest that such large structures are common
at z~3, with about one similar structure per survey field. The implied space
density is consistent with the possibility that we are observing moderately
rich clusters of galaxies in their early non-linear evolution. Finally, the
spectrum of one of the QSOs discovered in our survey (z_{em} = 3.356) exhibits
metal line absorption systems within the 3 redshift bins having the largest
number of galaxies in field, z = 2.93, 3.09, and 3.28. These results are the
first from an ongoing ``targeted'' redshift survey designed to explore the
nature and distribution of star-forming galaxies in the redshift range 2.7 <~ z
<~ 3.4.Comment: 24 pages including 5 ps figures, LaTeX, uses aaspp4.sty, to appear in
the Astrophysical Journal. Also available at
ftp://astro.caltech.edu/users/ccs/spike_preprint.ps.g
Development of intuitive rules: Evaluating the application of the dual-system framework to understanding children's intuitive reasoning
This is an author-created version of this article. The original source of publication is Psychon Bull Rev. 2006 Dec;13(6):935-53
The final publication is available at www.springerlink.com
Published version: http://dx.doi.org/10.3758/BF0321390
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