271 research outputs found
OMEGA AND BIASING FROM OPTICAL GALAXIES VERSUS POTENT MASS
The mass density field in the local universe, recovered by the POTENT method
from peculiar velocities of 3000 galaxies, is compared with the density
field of optically-selected galaxies. Both density fields are smoothed with a
Gaussian filter of radius 12 Mpc. Under the assumptions of
gravitational instability and a linear biasing parameter b\sbo between
optical galaxies and mass, we obtain \beta\sbo \equiv \om^{0.6}/b\sbo = 0.74
\pm 0.13. This result is obtained from a regression of POTENT mass density on
optical density after correcting the mass density field for systematic biases
in the velocity data and POTENT method. The error quoted is just the
formal error estimated from the observed scatter in the density--density
scatterplot; it does not include the uncertainty due to cosmic scatter in the
mean density or in the biasing relation. We do not attempt a formal analysis of
the goodness of fit, but the scatter about the fit is consistent with our
estimates of the uncertainties.Comment: Final revised version (minor typos corrected). 13 pages, gzipped tar
file containing LaTeX and figures. The Postscript file is available at
ftp://dust0.dur.ac.uk/pub/mjh/potopt/potopt.ps.Z or (gzipped) at
ftp://xxx.lanl.gov/astro-ph/ps/9501/9501074.ps.gz or via WWW at
http://xxx.lanl.gov/ps/astro-ph/9501074 or as separate LaTeX text and
encapsulated Postscript figures in a compressed tar'd file at
ftp://dust0.dur.ac.uk/pub/mjh/potopt/latex/potopt.tar.
Shellflow. I. The Convergence of the Velocity Field at 6000 km/s
We present the first results from the Shellflow program, an all-sky
Tully-Fisher (TF) peculiar velocity survey of 276 Sb-Sc galaxies with redshifts
between 4500 and 7000 km/s. Shellflow was designed to minimize systematic
errors between observing runs and between telescopes, thereby removing the
possibility of a spurious bulk flow caused by data inhomogeneity. A fit to the
data yields a bulk flow amplitude V_bulk = 70{+100}{-70} km/s (1 sigma error)
with respect to the Cosmic Microwave Background, i.e., consistent with being at
rest. At the 95% confidence level, the flow amplitude is < 300 km/s. Our
results are insensitive to which Galactic extinction maps we use, and to the
parameterization of the TF relation. The larger bulk motion found in analyses
of the Mark III peculiar velocity catalog are thus likely to be due to
non-uniformities between the subsamples making up Mark III. The absence of bulk
flow is consistent with the study of Giovanelli and collaborators and flow
field predictions from the observed distribution of IRAS galaxies.Comment: Accepted version for publication in ApJ. Includes an epitaph for
Jeffrey Alan Willick (Oct 8, 1959 - Jun 18, 2000
A Library of Integrated Spectra of Galactic Globular Clusters
We present a new library of integrated spectra of 40 Galactic globular
clusters, obtained with the Blanco 4-m telescope and the R-C spectrograph at
the Cerro Tololo Interamerican Observatory. The spectra cover the range ~ 3350
-- 6430 A with ~ 3.1 A (FWHM) resolution. The spectroscopic observations and
data reduction were designed to integrate the full projected area within the
cluster core radii in order to properly sample the light from stars in all
relevant evolutionary stages. The S/N values of the flux-calibrated spectra
range from 50 to 240/A at 4000 A and from 125 to 500/A at 5000 A. The selected
targets span a wide range of cluster parameters, including metallicity,
horizontal-branch morphology, Galactic coordinates, Galactocentric distance,
and concentration. The total sample is thus fairly representative of the entire
Galactic globular cluster population and should be valuable for comparison with
similar integrated spectra of unresolved stellar populations in remote systems.
For most of the library clusters, our spectra can be coupled with deep
color-magnitude diagrams and reliable metal abundances from the literature to
enable the calibration of stellar population synthesis models. In this paper we
present a detailed account of the observations and data reduction. The spectral
library is publicly available in electronic format from the National Optical
Astronomical Observatory website.Comment: 39 Pages, including 2 tables and 15 Figures. To appear in the
Astrophysical Journal, Supplement Serie
Disc-like Objects in Hierarchical Hydrodynamical Simulations: Comparison with Observations
We present results from a careful and detailed analysis of the structural and
dynamical properties of a sample of 29 disc-like objects identified at z=0 in
three AP3M-SPH fully consistent cosmological simulations. These simulations are
realizations of a CDM hierarchical model, where an inefficient Schmidt law-like
algorithm to model the stellar formation process has been implemented. We focus
on properties that can be constrained with available data from observations of
spiral galaxies, namely, the bulge and disc structural parameters and the
rotation curves. Comparisons with data from Broeils (1992), de Jong (1996) and
Courteau (1996, 1997) give satisfactory agreement, in contrast with previous
findings using other codes. This suggests that the stellar formation
implementation we have used has succeded in forming compact bulges that
stabilize disc-like structures in the violent phases of their assembly, while
in the quiescent phases the gas has cooled and collapsed according with the
Fall & Efstathiou standard model of disc formation.Comment: 22 pages, LaTeX; 14 figures; references updated. MNRAS, in pres
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