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 $\bar{\omega}_{N}$($\theta$) for $N$ = 2,...,7 for galaxies from the fifth data release of the Sloan Digital Sky Survey. Our parent sample is selected from galaxies with $18 \leq r < 21$, 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 $\bar{\omega}_{N}$($\theta$) on luminosity, redshift, and galaxy-type. We measure $\bar{\omega}_{N}$($\theta$) using oversampling techniques and use them to calculate the projected, $s_{N}$. Using models derived from theoretical power-spectra and perturbation theory, we measure the bias parameters $b_1$ and $c_2$, finding that the large differences in both bias parameters ($b_1$ and $c_2$) between early- and late-type galaxies are robust against changes in redshift, luminosity, and $\sigma_8$, 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 ($c_2$ is larger by $\sim0.5$ at $z > 0.3$) and small scales (large amplitudes are measured at small scales only for $z > 0.3$, suggesting much more merger driven star formation at $z > 0.3$). Finally, our measurements of $c_2$ suggest both that $\sigma_8 < 0.8$ and $c_2$ 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