35 research outputs found
A First Comparison of the SBF Survey Distances with the Galaxy Density Field: Implications for H_0 and Omega
We compare the peculiar velocities measured in the SBF Survey of Galaxy
Distances with the predictions from the density fields of the IRAS 1.2 Jy
flux-limited redshift survey and the Optical Redshift Survey (ORS) to derive
simultaneous constraints on the Hubble constant and the density parameter
, where is the linear bias. We find
and for the IRAS and ORS
comparisons, respectively, and \kmsMpc (with an additional 9%
uncertainty due to the Cepheids themselves). The match between predicted and
observed peculiar velocities is good for these values of and , and
although there is covariance between the two parameters, our results clearly
point toward low-density cosmologies. Thus, the unresolved discrepancy between
the ``velocity-velocity'' and ``density-density'' measurements of
continues.Comment: 4 pages with 3 embedded ps figures; uses emulateapj.sty (included).
Accepted for publication in ApJ Letter
Supermassive Black Holes and the Evolution of Galaxies
Black holes, an extreme consequence of the mathematics of General Relativity,
have long been suspected of being the prime movers of quasars, which emit more
energy than any other objects in the Universe. Recent evidence indicates that
supermassive black holes, which are probably quasar remnants, reside at the
centers of most galaxies. As our knowledge of the demographics of these relics
of a violent earlier Universe improve, we see tantalizing clues that they
participated intimately in the formation of galaxies and have strongly
influenced their present-day structure.Comment: 20 pages, - This is a near-duplicate of the paper in Nature 395, A14,
1998 (Oct 1
The Centers of Early-Type Galaxies with HST II: Empirical Models and Structural Parameters
We present a set of structural parameters for the central parts of 57
early-type galaxies observed with the Planetary Camera of the Hubble Space
Telescope. These parameters are based on a new empirical law that successfully
characterizes the centers of early type galaxies. This empirical law assumes
that the surface brightness profile is a combination of two power laws with
different slopes gamma and beta for the inner and outer regions. Conventional
structural parameters such as core radius and central surface brightness are
replaced by break radius r_b, where the transition between power-law slopes
takes place, and surface brightness mu_b at that radius. An additional
parameter alpha describes the sharpness of the break. The structural parameters
are derived using a chi-squared minimization process applied to the mean
surface brightness profiles. The resulting model profiles generally give very
good agreement to the observed profiles out to the radius of 10 arcseconds
imaged by the Planetary Camera. Exceptions include galaxies which depart from
pure power-laws at large radius, those with strong nuclear components, and
galaxies partly obscured by dust. The uncertainties in the derived parameters
are estimated using Monte-Carlo simulations which test the stability of
solutions in the face of photon noise and the effects of the deconvolution
process. The covariance of the structural parameters is examined by computing
contours of constant chi squared in multi-dimensional parameter space.Comment: 14 pages, 1 table, 8 postscript figures, aaspp4.sty included,
accepted for publication in the Astronomical Journa