11,063 research outputs found
The Cosmological Mean Density and its Local Variations Probed by Peculiar Velocities
Peculiar velocities thoughout the region of the local supercluster are
reconstructed by two different orbit-retracing methods. The requirement of the
optimal correlation between the radial components of reconstructed velocities
and the observed peculiar velocities derived from our extensive new catalog of
distances puts stringent constraints on the values of the cosmological
parameters. Our constraints intersect those from studies of microwave
background fluctuations and statistical properties of galaxy clustering: the
ensemble of constraints are consistent with Omega_m=0.22\pm 0.02. While motions
throughout the Local Supercluster provide a measure of the mean ratio of mass
to light, there can be large local fluctuations. Our reconstruction of the
infall velocities in the immediate vicinity of the Virgo Cluster shows that
there is a mass-to-light anomaly of a factor of 3 to 6 between groups in the
general field environment and the heavily populated Virgo Cluster.Comment: 4 pages, 2 figures, version to appear in Astrophysical Journal
Letter
The Scalar Sector in 331 Models
We calculate the exact tree-level scalar mass matrices resulting from
symmetry breaking using the most general gauge-invariant scalar potential of
the 331 model, both with and without the condition that lepton number is
conserved. Physical masses are also obtained in some cases, as well as
couplings to standard and exotic gauge bosons.Comment: LaTex, 15 page
Derivation of Distances with the Tully-Fisher Relation: The Antlia Cluster
The Tully-Fisher relation is a correlation between the luminosity and the HI
21cm line width in spiral galaxies (LLW relation). It is used to derive galaxy
distances in the interval 7 to 100 Mpc. Closer, the Cepheids, TRGB and Surface
Brightness Fluctuation methods give a better accuracy. Further, the SNIa are
luminous objects still available for distance measurement purposes, though with
a dramatically lower density grid of measurements on the sky. Galaxies in
clusters are all at the same distance from the observer. Thus the distance of
the cluster derived from a large number of galaxies (N) has an error reduced
according to the square root of N. However, not all galaxies in a cluster are
suitable for the LLW measurement. The selection criteria we use are explained
hereafter; the important point being to avoid Malmquist bias and to not
introduce any systematics in the distance measurement.Comment: Moriond0
Cosmological fluctuation growth in bimetric MOND
I look at the growth of weak density inhomogeneities of nonrelativistic
matter, in bimetric-MOND (BIMOND) cosmology. I concentrate on
matter-twin-matter-symmetric versions of BIMOND, and assume that, on average,
the universe is symmetrically populated in the two sectors. MOND effects are
absent in an exactly symmetric universe, apart from the appearance of a
cosmological constant, Lambda~(a0/c)^2. MOND effects-local and cosmological-do
enter when density inhomogeneities that differ in the two sectors appear and
develop. MOND later takes its standard form in systems that are islands
dominated by pure matter. I derive the nonrelativistic equations governing
small-scale fluctuation growth. The equations split into two uncoupled systems,
one for the sum, the other for the difference, of the fluctuations in the two
sectors. The former is governed strictly by Newtonian dynamics. The latter is
governed by MOND dynamics, which entails stronger gravity, and nonlinearity
even for the smallest of perturbations. These cause the difference to grow
faster than the sum, conducing to matter-twin-matter segregation. The
nonlinearity also causes interaction between nested perturbations on different
scales. Because matter and twin matter (TM) repel each other in the MOND
regime, matter inhomogeneities grow not only by their own self gravity, but
also through shepherding by flanking TM overdensitie. The relative importance
of gravity and pressure in the MOND system depends also on the strength of the
perturbation. The development of structure in the universe, in either sector,
thus depends crucially on two initial fluctuation spectra: that of matter alone
and that of the matter-TM difference. I also discuss the back reaction on
cosmology of BIMOND effects that appear as "phantom matter" resulting from
inhomogeneity differences between the two sectors.Comment: 14 pages. Some clarifications added. Version published in Phys. Rev.
Unified Brane Gravity: Cosmological Dark Matter from Scale Dependent Newton Constant
We analyze, within the framework of unified brane gravity, the weak-field
perturbations caused by the presence of matter on a 3-brane. Although deviating
from the Randall-Sundrum approach, the masslessness of the graviton is still
preserved. In particular, the four-dimensional Newton force law is recovered,
but serendipitously, the corresponding Newton constant is shown to be
necessarily lower than the one which governs FRW cosmology. This has the
potential to puzzle out cosmological dark matter. A subsequent conjecture
concerning galactic dark matter follows.Comment: 6 pages, to be published in Phys. Rev.
The Velocity Field from Type Ia Supernovae Matches the Gravity Field from Galaxy Surveys
We compare the peculiar velocities of nearby SNe Ia with those predicted by
the gravity fields of full sky galaxy catalogs. The method provides a powerful
test of the gravitational instability paradigm and strong constraints on the
density parameter beta = Omega^0.6/b. For 24 SNe Ia within 10,000 km/s we find
the observed SNe Ia peculiar velocities are well modeled by the predictions
derived from the 1.2 Jy IRAS survey and the Optical Redshift Survey (ORS). Our
best is 0.4 from IRAS, and 0.3 from the ORS, with beta>0.7 and
beta<0.15 ruled out at 95% confidence levels from the IRAS comparison.
Bootstrap resampling tests show these results to be robust in the mean and in
its error. The precision of this technique will improve as additional nearby
SNe Ia are discovered and monitored.Comment: 16 pages (LaTex), 3 postscript figure
Possible Local Spiral Counterparts to Compact Blue Galaxies at Intermediate Redshift
We identify nearby disk galaxies with optical structural parameters similar
to those of intermediate-redshift compact blue galaxies. By comparing HI and
optical emission-line widths, we show that the optical widths substantially
underestimate the true kinematic widths of the local galaxies. By analogy,
optical emission-line widths may underrepresent the masses of intermediate-z
compact objects. For the nearby galaxies, the compact blue morphology is the
result of tidally-triggered central star formation: we argue that interactions
and minor mergers may cause apparently compact morphology at higher redshift.Comment: 5 pages, uses emulateapj5 and psfig. To appear in ApJ
The LCO/Palomar 10,000 km/sec Cluster Survey. I. Properties of the Tully-Fisher Relation
The first results from a Tully-Fisher (TF) survey of cluster galaxies are
presented. The galaxies are drawn from fifteen Abell clusters that lie in the
redshift range 9000-12,000 km/sec and are distributed uniformly around the
celestial sky. The data set consists of R-band CCD photometry and long- slit
H-alpha spectroscopy. The rotation curves (RCs) are characterized by a turnover
radius (r_t) and an asymptotic velocity v_a, while the surface brightness
profiles are characterized in terms of an effective exponential surface
brightness I_e and a scale length r_e. The TF scatter is minimized when the
rotation velocity is measured at 2.0 +/- 0.2 r_e; a significantly larger
scatter results when the rotation velocity is measured at > 3 or < 1.5 scale
lengths. This effect demonstrates that RCs do not have a universal form, as has
been suggested by Persic, Salucci, and Stel. In contrast to previous studies, a
modest but statistically significant surface-brightness dependence of the TF
relation is found, log v = const + 0.28*log L + 0.14*log I_e. This indicates a
stronger parallel between the TF relation and the FP relations of elliptical
galaxies than has previously been recognized. Future papers in this series will
consider the implications of this cluster sample for deviations from Hubble
flow on 100-200 Mpc scales.Comment: 35 pages, 8 figures, uses aaspp4.sty. Submitted to ApJ. Also
available at http://astro.stanford.edu/jeff
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