410 research outputs found
Sidereal time analysis as a toll for the study of the space distribution of sources of gravitational waves
Gravitational wave (GW) detectors operating on a long time range can be used
for the study of space distribution of sources of GW bursts or to put strong
upper limits on the GW signal of a wide class of source candidates. For this
purpose we propose here a sidereal time analysis to analyze the output signal
of GW detectors. Using the characteristics of some existing detectors, we
demonstrate the capability of the sidereal time analysis to give a clear
signature of different localizations of GW sources: the Galactic Center, the
Galactic Plane, the Supergalactic plane, the Great Attractor. On the contrary,
a homogeneous 3D-distribution of GW sources gives a signal without features. In
this paper we consider tensor gravitational waves with randomly oriented
polarization. We consider GW detectors at fixed positions on the Earth, and a
fixed orientation of the antenna.Comment: 7 pages, 6 figure
Reduction of the COSMOS Southern Sky galaxy survey data to the RC3 standard system
After having cross-identified a subsample of LEDA galaxies in the COSMOS
database, we defined the best relations to convert COSMOS parameters
(coordinates, position angle, diameter, axis ratio and apparent magnitude) into
RC3 system used in the LEDA database. Tiny secondary effects can be tested:
distance to plate cenetrs effect and air-mass effect. The converted COSMOS
parameters are used to add missing parameters on LEDA galaxies.
Key words: galaxies - catalogue - photometryComment: 5 pages, postcript including figures, to appear in MNRAS, reprint
requests: [email protected]
Are the Perseus-Pisces chain and the Pavo-Indus wall connected?
A significant empty region was found between the southern Pavo- Indus (PI)
wall and the northern Perseus-Pisces (PP) chain. This survey tests the reality
of this void which may simply reflect previous poor sampling of the galaxies in
this region. Redshifts for a magnitude selected sample of 379 galaxies were
obtained covering the four UKST/SERC survey fields with Bt <= 17.0. All
redshifts were obtained with the FLAIR multi-object spectroscopy system on the
1.2 m U.K. Schmidt Telescope at Siding Spring, Australia. Two highly
significant density enhancements were found in the galaxy distribution at 133
Mpc and 200 Mpc (Ho=75 km/s/Mpc). We claim that no connexion exists between PP
and PI. However, a southern extension of PP was detected and makes the total
length of this chain of more than 150 Mpc.Comment: 14 pages, postscript including tables and figures
FERENGI: Redshifting galaxies from SDSS to GEMS, STAGES and COSMOS
We describe the creation of a set of artificially "redshifted" galaxies in
the range 0.1<z<1.1 using a set of ~100 SDSS low redshift (v<7000 km/s) images
as input. The intention is to generate a training set of realistic images of
galaxies of diverse morphologies and a large range of redshifts for the GEMS
and COSMOS galaxy evolution projects. This training set allows other studies to
investigate and quantify the effects of cosmological redshift on the
determination of galaxy morphologies, distortions and other galaxy properties
that are potentially sensitive to resolution, surface brightness and bandpass
issues. We use galaxy images from the SDSS in the u, g, r, i, z filter bands as
input, and computed new galaxy images from these data, resembling the same
galaxies as located at redshifts 0.1<z<1.1 and viewed with the Hubble Space
Telescope Advanced Camera for Surveys (HST ACS). In this process we take into
account angular size change, cosmological surface brightness dimming, and
spectral change. The latter is achieved by interpolating a spectral energy
distribution that is fit to the input images on a pixel-to-pixel basis. The
output images are created for the specific HST ACS point spread function and
the filters used for GEMS (F606W and F850LP) and COSMOS (F814W). All images are
binned onto the desired pixel grids (0.03" for GEMS and 0.05" for COSMOS) and
corrected to an appropriate point spread function. Noise is added corresponding
to the data quality of the two projects and the images are added onto empty sky
pieces of real data images. We make these datasets available from our website,
as well as the code - FERENGI: "Full and Efficient Redshifting of Ensembles of
Nearby Galaxy Images" - to produce datasets for other redshifts and/or
instruments.Comment: 11 pages, 10 figures, 3 table
Luminosity density estimation from redshift surveys and the mass density of the Universe
In most direct estimates of the mass density (visible or dark) of the
Universe, a central input parameter is the luminosity density of the Universe.
Here we consider the measurement of this luminosity density from red-shift
surveys, as a function of the yet undetermined characteristic scale R_H at
which the spatial distribution of visible matter tends to a well defined
homogeneity. Making the canonical assumption that the cluster mass to
luminosity ratio M/L is the universal one, we can estimate the total mass
density as a function \Omega_m(R_H,M/L). Taking the highest estimated cluster
value M/L ~300h and a conservative lower limit R_H > 20 Mpc/h, we obtain the
upper bound \Omega_m < 0.1 . We note that for values of the homogeneity scale
R_H in the range R_H ~ (90 +/- 45) hMpc, the value of \Omega_m may be
compatible with the nucleosynthesis inferred density in baryons.Comment: 16 pages, latex, no figures. To be published in Astrophysical Journal
Letter
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