2,097 research outputs found

### K-band versus I-band Surface Brightness Fluctuations as distance indicators

We evaluate the method of optical and infrared Surface Brightness
Fluctuations (SBF) as a distance indicator and its application on 8-m class
telescopes, such as the Very Large Telescope (VLT). The novelty of our approach
resides in the development of Monte Carlo simulations of SBF observations
incorporating realistic elliptical galaxy stellar population models, the
effects induced by globular clusters and background galaxies, instrumental
noise, sky background and PSF blurring. We discuss, for each band and in
different observational conditions, the errors on distance measurements arising
from stellar population effects, data treatment and observational constraints.
With 8-m class telescopes, one can extend I-band SBF measurements out to
6000-10000 km/s. Integration times in the K-band are too expensive from the
ground, due to the high infrared background for large-scale distance
determination projects. Nevertheless ground-based K-band measurements are
necessary to understand stellar population effects on the SBF calibration, and
to prepare future space-based observations, where this band is more efficient.Comment: A&A, in press, 17 pages, 10 figure

### 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 $H_0$ and the density parameter
$\beta = \Omega^{0.6}/b$, where $b$ is the linear bias. We find
$\beta_I=0.42^{+0.10}_{-0.06}$ and $\beta_O=0.26\pm0.08$ for the IRAS and ORS
comparisons, respectively, and $H_0=74\pm4$ \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 $H_0$ and $\beta$, 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 $\beta$
continues.Comment: 4 pages with 3 embedded ps figures; uses emulateapj.sty (included).
Accepted for publication in ApJ Letter

### Redshift-Independent Distances to Type Ia Supernovae

We describe a procedure for accurately determining luminosity distances to
Type Ia supernovae (SNe Ia) without knowledge of redshift. This procedure,
which may be used as an extension of any of the various distance determination
methods currently in use, is based on marginalizing over redshift, removing the
requirement of knowing $z$ a priori. We demonstrate that the Hubble diagram
scatter of distances measured with this technique is approximately equal to
that of distances derived from conventional redshift-specific methods for a set
of 60 nearby SNe Ia. This indicates that accurate distances for cosmological
SNe Ia may be determined without the requirement of spectroscopic redshifts,
which are typically the limiting factor for the number of SNe that modern
surveys can collect. Removing this limitation would greatly increase the number
of SNe for which current and future SN surveys will be able to accurately
measure distance. The method may also be able to be used for high-$z$ SNe Ia to
determine cosmological density parameters without redshift information.Comment: 12 pages, 3 figures, accepted for publication in Astrophysical
Journal Letter

### Redshifts of the Gravitational Lenses MG1131+0456 and B1938+666

The redshifts of the gravitational lens galaxies in MG1131+0456 and B1938+666
are 0.844 and 0.881 respectively. Both are early-type galaxies lying at the
redshifts predicted by assuming that they are early-type galaxies with old
stellar populations lying on the fundamental plane. We also find evidence for a
foreground group of galaxies at z=0.343 near MG1131+0456. The source redshifts
are predicted to be >1.8 in both systems, but they are so red that infrared
spectra will be required to determine their redshifts.Comment: 10 pages, AASTeX Latex, including 1 JPEG and 2 postscript figures,
submitted to Astronomical Journal Minor typos fixe

### Discovery of Non-radial pulsations in PQ Andromedae

We have detected pulsations in time-series photometry of the WZ Sge dwarf
nova PQ And. The strongest peak in the power spectrum occurs at a period of
10.5 minutes. Similar periods have been observed in other WZ Sge systems and
are attributed to ZZ Ceti type non-radial pulsations. There is no indication in
the photometry of an approximately 1.7 hour orbital period as reported in
previous spectroscopic observations.Comment: 7 pages, 5 figure

### Asymmetric Drift and the Stellar Velocity Ellipsoid

We present the decomposition of the stellar velocity ellipsoid using stellar
velocity dispersions within a 40 deg wedge about the major-axis (sigma_maj),
the epicycle approximation, and the asymmetric drift equation. Thus, we employ
no fitted forms for sigma_maj and escape interpolation errors resulting from
comparisons of the major and minor axes. We apply the theoretical construction
of the method to integral field data taken for NGC 3949 and NGC 3982. We derive
the vertical-to-radial velocity dispersion ratio (sigma_z / sigma_R) and find
(1) our decomposition method is accurate and reasonable, (2) NGC 3982 appears
to be rather typical of an Sb type galaxy with sigma_z / sigma_R = 0.73
(+0.13/-0.11) despite its high surface brightness and small size, and (3) NGC
3949 has a hot disk with sigma_z / sigma_R = 1.18 (+0.36/-0.28).Comment: 4 pages including 3 figures, to appear in "Island Universes:
Structure and Evolution of Disk Galaxies", Terschelling, Netherlands, July
3-8, 200

### Tomography of Collisionless Stellar Systems

In this paper the concept of tomography of a collisionless stellar system of
general shape is introduced, and a generalization of the Projected Virial
Theorem is obtained. Applying the tomographic procedure we then derive a new
family of virial equations which coincides with the already known ones for
spherically symmetric systems. This result is obtained without any use of
explicit expressions for the line-of-sight velocity dispersion, or spherical
coordinate system.Comment: BAP-06-1994-016-OAB. 7 pages, postscript file. In press on Celestial
Mechanic

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