852 research outputs found
Void probability as a function of the void's shape and scale-invariant models
The dependence of counts in cells on the shape of the cell for the large scale galaxy distribution is studied. A very concrete prediction can be done concerning the void distribution for scale invariant models. The prediction is tested on a sample of the CfA catalog, and good agreement is found. It is observed that the probability of a cell to be occupied is bigger for some elongated cells. A phenomenological scale invariant model for the observed distribution of the counts in cells, an extension of the negative binomial distribution, is presented in order to illustrate how this dependence can be quantitatively determined. An original, intuitive derivation of this model is presented
Higher-Order Angular Galaxy Correlations in the SDSS: Redshift and Color Dependence of non-Linear Bias
We present estimates of the N-point galaxy, area-averaged, angular
correlation functions () for = 2,...,7 for
galaxies from the fifth data release of the Sloan Digital Sky Survey. Our
parent sample is selected from galaxies with , and is the
largest ever used to study higher-order correlations. We subdivide this parent
sample into two volume limited samples using photometric redshifts, and these
two samples are further subdivided by magnitude, redshift, and color (producing
early- and late-type galaxy samples) to determine the dependence of
() on luminosity, redshift, and galaxy-type. We
measure () using oversampling techniques and use them
to calculate the projected, . Using models derived from theoretical
power-spectra and perturbation theory, we measure the bias parameters and
, finding that the large differences in both bias parameters ( and
) between early- and late-type galaxies are robust against changes in
redshift, luminosity, and , and that both terms are consistently
smaller for late-type galaxies. By directly comparing their higher-order
correlation measurements, we find large differences in the clustering of
late-type galaxies at redshifts lower than 0.3 and those at redshifts higher
than 0.3, both at large scales ( is larger by at ) and
small scales (large amplitudes are measured at small scales only for ,
suggesting much more merger driven star formation at ). Finally, our
measurements of suggest both that and is negative.Comment: 46 pages, 19 figures, Accepted to Ap
On the CCD Calibration of Zwicky galaxy magnitudes & The Properties of Nearby Field Galaxies
We present CCD photometry for galaxies around 204 bright (m_Z < 15.5) Zwicky
galaxies in the equatorial extension of the APM Galaxy Survey, sampling and
area over 400 square degrees, which extends 6 hours in right ascension. We fit
a best linear relation between the Zwicky magnitude system, m_Z, and the CCD
photometry, B, by doing a likehood analysis that corrects for Malmquist bias.
This fit yields a mean scale error in Zwicky of 0.38 mag per magnitude: ie
Delta m_Z = (0.62 \pm 0.05) Delta B and a mean zero point of = -0.35
\pm 0.15 mag. The scatter around this fit is about 0.4 mag. Correcting the
Zwicky magnitude system with the best fit model results in a 60% lower
normalization and 0.35 mag brighter M_* in the luminosity function. This brings
the CfA2 luminosity function closer to the other low redshift estimations (eg
Stromlo-APM or LCRS). We find a significant positive angular correlation of
magnitudes and position in the sky at scales smaller than about 5 armin, which
corresponds to a mean separation of 120 Kpc/h. We also present colours, sizes
and ellipticities for galaxies in our fields which provides a good local
reference for the studies of galaxy evolution.Comment: Full size figures can be found in
http://www.ieec.fcr.es/cosmo-www/zwicky.ps Version accepted for publication
in MNRAS. Extended discussion on properties of nearby galaxies. References
added. An inconsistency in the R band isophote used has been corrected. Main
results and conclusions are unchange
Reconstruction of cosmological density and velocity fields in the Lagrangian Zel'dovich Approximation
We present a method for reconstructing cosmological densityn for and velocity
fields using the Lagrangian Zel'dovich formalism. . The method involves finding
the least action solution for straight line particle paths in an evolving
density field. Our starting point is the final, evolved density , so that we
are in effect carrying out the standard Zel'dovich Approximation based process
in reverse. Using a simple numerical algorithm we are able to minimise the
action for the trajectories of several million particles. We apply our method
to the evolved density taken from N-body simulations of different cold dark
matter dominated universes, testing both the prediction for the present day
velocity field and for the initial density field. The method is easy to apply,
reproduces the accuracy of the forward Zel'dovich Approximation, and also works
directly in redshift space with minimal modification.Comment: 13 pages with only 2 (out 9) figures. MNRAS in press. New Appendix
shows the relation between shell crossing and PIZA. A completed version with
all 9 figures available by anonymous ftp at
ftp://bessel.mps.ohio-state.edu/pub/racc/piza.ps.gz (USA) or
ftp://ftp-astro.physics.ox.ac.uk/pub/eg/piza3.ps.gz (UK
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