8,661 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
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
A Face-On Tully-Fisher Relation
We construct the first "face-on" Tully-Fisher (TF) relation for 24 galaxies
with inclinations between 16 degrees and 41 degrees. The enabling measurements
are integral-field, echelle spectroscopy from the WIYN 3.5m telescope, which
yield accurate kinematic estimates of disk inclination to 15 degrees. Kinematic
inclinations are of sufficient accuracy that our measured TF scatter of 0.42
mag is comparable to other surveys even without internal-absorption
corrections. Three of four galaxies with significant kinematic and photometric
asymmetries also have the largest deviations from our TF relation, suggesting
that asymmetries make an important contribution to TF scatter. By measuring
inclinations below 40 degrees, we establish a direct path to linking this
scatter to the unprojected structure of disks and making non-degenerate
dynamical mass-decompositions of spiral galaxies.Comment: 13 pages, 3 figures (2 color). Accepted for publication in ApJ
Letter
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.
Constraints on the Massive Supernova Progenitors
Generally accepted scheme distinguishes two main classes of supernovae (SNe):
Ia resulting from the old stellar population (deflagration of a white dwarf in
close binary systems), and SNe of type II and Ib/c whose ancestors are young
massive stars (died in a core-collapse explosion). Concerning the latter, there
are suggestions that the SNe II are connected to early B stars, and SNe Ib/c to
isolated O or Wolf-Rayet (W-R) stars. However, little or no effort was made to
further separate SNe Ib from Ic. We have used assumed SN rates for different SN
types in spiral galaxies in an attempt to perform this task. If isolated
progenitor hypothesis is correct, our analysis indicates that SNe Ib result
from stars of main-sequence mass , while the progenitors of SNe Ic are more
massive stars with .
Alternatively, if the majority of SNe Ib/c appear in close binary systems
(CBs) then they would result from the same progenitor population as most of the
SNe II, i.e. early B stars with initial masses of order . Future observations of SNe at high-redshift () and
their rate will provide us with unique information on SN progenitors and
star-formation history of galaxies. At higher- (deeper in the cosmic past)
we expect to see the lack of type Ia events, i.e. the dominance of
core-collapse SNe. Better understanding of the stripped-envelope SNe (Ib/c),
and their potential use as distance indicators at high-, would therefore be
of great practical importance.Comment: 11 pages, 2 figures, accepted for publication in IJMP
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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