2,052 research outputs found
Distances from Surface Brightness Fluctuations
The practice of measuring galaxy distances from their spatial fluctuations in
surface brightness is now a decade old. While several past articles have
included some review material, this is the first intended as a comprehensive
review of the surface brightness fluctuation (SBF) method. The method is
conceptually quite simple, the basic idea being that nearby (but unresolved)
star clusters and galaxies appear "bumpy", while more distant ones appear
smooth. This is quantified via a measurement of the amplitude of the Poisson
fluctuations in the number of unresolved stars encompassed by a CCD pixel
(usually in an image of an elliptical galaxy). Here, we describe the technical
details and difficulties involved in making SBF measurements, discuss
theoretical and empirical calibrations of the method, and review the numerous
applications of the method from the ground and space, in the optical and
near-infrared. We include discussions of stellar population effects and the
"universality" of the SBF standard candle. A final section considers the future
of the method.Comment: Invited review article to appear in: `Post-Hipparcos Cosmic Candles',
A. Heck & F. Caputo (Eds), Kluwer Academic Publ., Dordrecht, in press. 22
pages, including 3 postscript figures; uses Kluwer's crckapb.sty LaTex macro
file, enclose
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
Potential of the Surface Brightness Fluctuations method to measure distances to dwarf elliptical galaxies in nearby clusters
The potential of the Surface Brightness Fluctuations (SBF) method to
determine the membership of dwarf elliptical galaxies (dEs) in nearby galaxy
clusters is investigated. Extensive simulations for SBF measurements on dEs in
the I-band for various combinations of distance modulus, seeing and integration
time are presented, based on average VLT FORS1 and FORS2 zero points. These
show that for distances up to 20 Mpc (Fornax or Virgo cluster distance),
reliable membership determination of dEs can be obtained down to very faint
magnitudes -10<M_V<-12 mag (25 mag / arcsec^2) within integration times of the
order of 1 hour and with good seeing. Comparing the limiting magnitudes of the
method for the different simulated observing conditions we derive some simple
rules to calculate integration time and seeing needed to reach a determined
limiting magnitude at a given distance modulus for observing conditions
different to the ones adopted in the simulations. Our simulations show a small
offset of the order of 0.15 mag towards measuring too faint SBF. It is shown
that this is due to loss of fluctuation signal when recovering pixel-to-pixel
fluctuations from a seeing convolved image. To check whether our simulations
represent well the behaviour of real data, SBF measurements for a real and
simulated sample of bright Centaurus Cluster dEs are presented. They show that
our simulations are in good agreement with the achievable S/N of SBF
measurements on real galaxies.Comment: 12 pages, 8 figures, accepted by A&A, replaced by version with
non-abridged bottom page limi
On surface brightness fluctuations: probabilistic and statistical bases I: Stellar population and theoretical SBF
This work aims to provide a theoretical formulation of Surface Brightness
Fluctuations (SBF) in the framework of probabilistic synthesis models, and to
distinguish between the different distributions involved in the SBF definition.
RESULTS: We propose three definitions of SBF: (i) stellar population SBF, which
can be computed from synthesis models and provide an intrinsic metric of fit
for stellar population studies; (ii) theoretical SBF, which include the stellar
population SBF plus an additional term that takes into account the distribution
of the number of stars per resolution element psi(N); theoretical SBF coincide
with Tonry & Schneider (1998) definition in the very particular case that
psi(N) is assumed to be a Poisson distribution. However, the Poisson
contribution to theoretical SBF is around 0.1% of the contribution due to the
stellar population SBF, so there is no justification to include any reference
to Poisson statistics in the SBF definition; (iii) observational SBF, which are
those obtained in observations that are distributed around the theoretical SBF.
Finally, we show alternative ways to compute SBF and extend the application of
stellar population SBF to defining a metric of fitting for standard stellar
population studies. CONCLUSIONS: We demostrate that SBF are observational
evidence of a probabilistic paradigm in population synthesis, where integrated
luminosities have an intrinsic distributed nature, and they rule out the
commonly assumed deterministic paradigm of stellar population modeling.Comment: A&A accepte
The Infrared Surface Brightness Fluctuation Distances to the Hydra and Coma Clusters
We present IR surface brightness fluctuation (SBF) distance measurements to
NGC 4889 in the Coma cluster and to NGC 3309 and NGC 3311 in the Hydra cluster.
We explicitly corrected for the contributions to the fluctuations from globular
clusters, background galaxies, and residual background variance. We measured a
distance of 85 +/- 10 Mpc to NGC 4889 and a distance of 46 +/- 5 Mpc to the
Hydra cluster. Adopting recession velocities of 7186 +/- 428 km/s for Coma and
4054 +/- 296 km/s for Hydra gives a mean Hubble constant of H_0 = 87 +/- 11
km/s/Mpc. Corrections for residual variances were a significant fraction of the
SBF signal measured, and, if underestimated, would bias our measurement towards
smaller distances and larger values of H_0. Both NICMOS on the Hubble Space
Telescope and large-aperture ground-based telescopes with new IR detectors will
make accurate SBF distance measurements possible to 100 Mpc and beyond.Comment: 24 pages, 4 PostScript figures, 2 JPEG images; accepted for
publication in Ap
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
A CO Survey of Gravitationally Lensed Quasars with the IRAM Interferometer
We present the results of a CO survey of gravitationally lensed quasars,
conducted with the Plateau de Bure Interferometer over the last three years.
Among the 18 objects surveyed, one was detected in CO line emission, while six
were detected in the continuum at 3mm and three in the continuum at 1mm. The
low CO detection rate may at least in part be due to uncertainties in the
redshifts derived from quasar broad emission lines. The detected CO source, the
z=3.2 radio quiet quasar MG0751+2716, is quite strong in the CO(4-3) line and
in the millimeter/submillimeter continuum, the latter being emission from cool
dust. The integrated CO line flux is 5.96 +- 0.45 Jy.km/s, and the total
molecular gas mass is estimated to be in the range M(H_2) = 1.6-3.1 X 10^9
solar masses.Comment: 5 pages, 2 figures, uses aa.cls and psfig.st
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
Dark Matter Relic Abundance and Scalar-Tensor Dark Energy
Scalar-tensor theories of gravity provide a consistent framework to
accommodate an ultra-light quintessence scalar field. While the equivalence
principle is respected by construction, deviations from General Relativity and
standard cosmology may show up at nucleosynthesis, CMB, and solar system tests
of gravity. After imposing all the bounds coming from these observations, we
consider the expansion rate of the universe at WIMP decoupling, showing that it
can lead to an enhancement of the dark matter relic density up to few orders of
magnitude with respect to the standard case. This effect can have an impact on
supersymmetric candidates for dark matter.Comment: 12 pages, 13 figures; V2: references added, matches published versio
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