119 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
On the kinematics of the Local cosmic void
We collected the existing data on the distances and radial velocities of
galaxies around the Local Void in the Aquila/Hercules to examine the peculiar
velocity field induced by its underdensity. A sample of 1056 galaxies with
distances measured from the Tip of the Red Giant Branch, the Cepheid
luminosity, the SNIa luminosity, the surface brightness fluctuation method, and
the Tully-Fisher relation has been used for this purpose. The amplitude of
outflow is found to be ~300 km/s. The galaxies located within the void produce
the mean intra-void number density about 1/5 of the mean external number
density of galaxies. The void's population has a lower luminosity and a later
morphological type with the medians: M_B = -15.7^m and T = 8 (Sdm),
respectively.Comment: Version 1. 14 pages, 8 figures, 2 tables. Accepted to Astrophysics,
Volume 54, Issue
Dark Matter, Muon g-2 and Other SUSY Constraints
Recent developments constraining the SUSY parameter space are reviewed within
the framework of SUGRA GUT models. The WMAP data is seen to reduce the error in
the density of cold dark matter by about a factor of four, implying that the
lightest stau is only 5 -10 GeV heavier than the lightest neutralino when m_0,
m_{1/2} < 1 TeV. The CMD-2 re-analysis of their data has reduced the
disagreement between the Standard Model prediction and the Brookhaven
measurement of the muon magnetic moment to 1.9 sigma, while using the tau decay
data plus CVC, the disagreement is 0.7 sigma. (However, the two sets of data
remain inconsistent at the 2.9 sigma level.) The recent Belle and BABAR
measurements of the B -> phi K CP violating parameters and branching ratios are
discussed. They are analyzed theoretically within the BBNS improved
factorization method. The CP parameters are in disagreement with the Standard
Model at the 2.7 sigma level, and the branching ratios are low by a factor of
two or more over most of the parameter space. It is shown that both anomalies
can naturally be accounted for by adding a non-universal cubic soft breaking
term at M_G mixing the second and third generations.Comment: 16 pages, 7 figures, plenary talk at Beyond The Desert '03, Castle
Ringberg, Germany, June 9, 2003. Typos correcte
Non-BBN Constraints On The Key Cosmological Parameters
Since the baryon-to-photon ratio "eta" is in some doubt at present, we ignore
the constraints on eta from big bang nucleosynthesis (BBN) and fit the three
key cosmological parameters (h, Omega_M, eta) to four other observational
constraints: Hubble parameter, age of the universe, cluster gas (baryon)
fraction, and effective shape parameter "Gamma". We consider open and flat CDM
models and flat "Lambda"-CDM models, testing goodness of fit and drawing
confidence regions by the Delta-chi^2 method. CDM models with Omega_M = 1 (SCDM
models) are accepted only because we allow a large error on h, permitting h <
0.5. Open CDM models are accepted only for Omega_M \gsim 0.4. Lambda-CDM models
give similar results. In all of these models, large eta (\gsim 6) is favored
strongly over small eta, supporting reports of low deuterium abundances on some
QSO lines of sight, and suggesting that observational determinations of
primordial 4He may be contaminated by systematic errors. Only if we drop the
crucial Gamma constraint are much lower values of Omega_M and eta permitted.Comment: 12 pages, Kluwer Latex, 2 Postscript figures, to appear in the
proceedings of the ISSI Workshop, "The Primordial Nuclei and Their Galactic
Evolution" (Bern, May 6-10, 1997), ed. N. Prantzos, M. Tosi, and R. von
Steiger (Kluwer, Dordrecht
Blueshifted galaxies in the Virgo Cluster
We examine a sample of 65 galaxies in the Virgo cluster with negative radial
velocities relative to the Local Group. Some features of this sample are
pointed out. All of these objects are positioned compactly within a virial zone
of radius 6{\deg} in the cluster, but their centroid is displaced relative to
the dynamic center of the cluster, M87, by 1.1{\deg} to the northwest. The
dwarf galaxies in this sample are clumped on a scale of ~10' (50 kpc). The
observed asymmetry in the distribution of the blueshifted galaxies may be
caused by infall of a group of galaxies around M86 onto the main body of the
cluster. We offer another attempt to explain this phenomenon, assuming a mutual
tangential velocity of ~300 km/s between the Local Group and the Virgo cluster
owing to their being repelled from the local cosmological void.Comment: 10 pages, 4 figures, 1 table. Published in Astrophysics, Vol. 53, No.
1, pp. 32-41, 201
The White Dwarf Luminosity Functions from the Pan-STARRS 1 3π Steradian Survey
A large sample of white dwarfs is selected by both proper motion and colours from the Pan-STARRS 1 3{\pi} Steradian Survey Processing Version 2 to construct the White Dwarf Luminosity Functions of the discs and halo in the solar neighbourhood. Four-parameter astrometric solutions were recomputed from the epoch data. The generalised maximum volume method is then used to calculate the density of the populations. After removal of crowded areas near the Galactic plane and centre, the final sky area used by this work is 7.833 sr, which is 83% of the 3{\pi} sky and 62% of the whole sky. By dividing the sky using Voronoi tessellation, photometric and astrometric uncertainties are recomputed at each step of the integration to improve the accuracy of the maximum volume. Interstellar reddening is considered throughout the work. We find a disc-to-halo white dwarf ratio of about 100
A very faint core-collapse supernova in M85
An anomalous transient in the early Hubble-type (S0) galaxy Messier 85 (M85)
in the Virgo cluster was discovered by Kulkarni et al. (2007) on 7 January 2006
that had very low luminosity (peak absolute R-band magnitude MR of about -12)
that was constant over more than 80 days, red colour and narrow spectral lines,
which seem inconsistent with those observed in any known class of transient
events. Kulkarni et al. (2007) suggest an exotic stellar merger as the possible
origin. An alternative explanation is that the transient in M85 was a type
II-plateau supernova of extremely low luminosity, exploding in a lenticular
galaxy with residual star-forming activity. This intriguing transient might be
the faintest supernova that has ever been discovered.Comment: 7 pages, 2 figures. Submitted to Nature "Brief Communication Arising"
on 18 July 2007, Accepted on 17 August 2007. Arising from: Kulkarni et al.
2007, Nature, 447, 458-46
Discovery of the progenitor of the type Ia supernova 2007on
Type Ia supernovae are exploding stars that are used to measure the
accelerated expansion of the Universe and are responsible for most of the iron
ever produced. Although there is general agreement that the exploding star is a
white dwarf in a binary system, the exact configuration and trigger of the
explosion is unclear, which could hamper their use for precision cosmology. Two
families of progenitor models have been proposed. In the first, a white dwarf
accretes material from a companion until it exceeds the Chandrasekhar mass,
collapses and explodes. Alternatively, two white dwarfs merge, again causing
catastrophic collapse and an explosion. It has hitherto been impossible to
determine if either model is correct. Here we report the discovery of an object
in pre-supernova archival X-ray images at the position of the recent type Ia
supernova (2007on) in the elliptical galaxy NGC 1404. Deep optical images (also
archival) show no sign of this object. From this we conclude that the X-ray
source is the progenitor of the supernova, which favours the accretion model
for this supernova, although the host galaxy is older (6-9 Gyr) than the age at
which the explosions are predicted in the accreting models.Comment: Published in Nature See also the two follow-up papers: Roelofs,
Bassa, Voss, Nelemans Nelemans, Voss, Roelofs, Bassa both on astro-ph
02/15/0
The Hubble Constant from Observations of the Brightest Red Giant Stars in a Virgo-Cluster Galaxy
The Virgo and Fornax clusters of galaxies play central roles in determining
the Hubble constant H_0. A powerful and direct way of establishing distances
for elliptical galaxies is to use the luminosities of the brightest red-giant
stars (the TRGB luminosity, at M_I = -4.2). Here we report the direct
observation of the TRGB stars in a dwarf elliptical galaxy in the Virgo
cluster. We find its distance to be 15.7 +- 1.5 Megaparsecs, from which we
estimate a Hubble constant of H_0 = 77 +- 8 km/s/Mpc. Under the assumption of a
low-density Universe with the simplest cosmology, the age of the Universe is no
more than 12-13 billion years.Comment: 12 pages, LaTeX, with 2 postscript figures; in press for Nature, July
199
Gravitational detection of a low-mass dark satellite at cosmological distance
The mass-function of dwarf satellite galaxies that are observed around Local
Group galaxies substantially differs from simulations based on cold dark
matter: the simulations predict many more dwarf galaxies than are seen. The
Local Group, however, may be anomalous in this regard. A massive dark satellite
in an early-type lens galaxy at z = 0.222 was recently found using a new method
based on gravitational lensing, suggesting that the mass fraction contained in
substructure could be higher than is predicted from simulations. The lack of
very low mass detections, however, prohibited any constraint on their mass
function. Here we report the presence of a 1.9 +/- 0.1 x 10^8 M_sun dark
satellite in the Einstein-ring system JVAS B1938+666 at z = 0.881, where M_sun
denotes solar mass. This satellite galaxy has a mass similar to the Sagittarius
galaxy, which is a satellite of the Milky Way. We determine the logarithmic
slope of the mass function for substructure beyond the local Universe to be
alpha = 1.1^+0.6_-0.4, with an average mass-fraction of f = 3.3^+3.6_-1.8 %, by
combining data on both of these recently discovered galaxies. Our results are
consistent with the predictions from cold dark matter simulations at the 95 per
cent confidence level, and therefore agree with the view that galaxies formed
hierarchically in a Universe composed of cold dark matter.Comment: 25 pages, 7 figures, accepted for publication in Nature (19 January
2012
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