How Stochastic is the Relative Bias Between Galaxy Types?

Abstract

Examining the nature of the relative clustering of different galaxy types can help tell us how galaxies formed. To measure this relative clustering, I perform a joint counts-in-cells analysis of galaxies of different spectral types in the Las Campanas Redshift Survey (LCRS). I develop a maximum-likelihood technique to fit for the relationship between the density fields of early- and late-type galaxies. This technique can directly measure nonlinearity and stochasticity in the biasing relation. At high significance, a small amount of stochasticity is measured, corresponding to a correlation coefficient of about 0.87 on scales corresponding to 15 Mpc/h spheres. A large proportion of this signal appears to derive from errors in the selection function, and a more realistic estimate finds a correlation coefficient of about 0.95. These selection function errors probably account for the large stochasticity measured by Tegmark & Bromley (1999), and may have affected measurements of very large-scale structure in the LCRS. Analysis of the data and of mock catalogs shows that the peculiar geometry, variable flux limits, and central surface-brightness selection effects of the LCRS do not seem to cause the effect.Comment: 38 pages, 14 figures. Submitted to Apj. Modified from a chapter of my Ph.D. Thesis at Princeton University, available at http://www-astro-theory.fnal.gov/Personal/blanton/thesis/index.htm