Measuring galaxy segregation using the mark connection function

TL;DR

This paper reviews and introduces spatial marked statistics, especially the mark connection function, to analyze galaxy clustering based on properties like luminosity and morphology, demonstrating their effectiveness with 2dFGRS data.

Contribution

It introduces the mark connection function as a new method for analyzing galaxy mark correlations and compares it with existing spatial marked statistics.

Findings

Passive galaxies show stronger clustering than active ones at small scales.

The mark connection function effectively characterizes spatial correlations between galaxy properties.

Different methods reveal various aspects of galaxy mark dependence and clustering.

Abstract

(abridged) The clustering properties of galaxies belonging to different luminosity ranges or having different morphological types are different. These characteristics or `marks' permit to understand the galaxy catalogs that carry all this information as realizations of marked point processes. Many attempts have been presented to quantify the dependence of the clustering of galaxies on their inner properties. The present paper summarizes methods on spatial marked statistics used in cosmology to disentangle luminosity, colour or morphological segregation and introduces a new one in this context, the mark connection function. The methods used here are the partial correlation functions, including the cross-correlation function, the normalised mark correlation function, the mark variogram and the mark connection function. All these methods are applied to a volume-limited sample drawn from the 2dFGRS, using the spectral type as the mark. We show the virtues of each method to provide information about the clustering properties of each population, the dependence of the clustering on the marks, the similarity of the marks as a function of the pair distances, and the way to characterise the spatial correlation between the marks. We demonstrate by means of these statistics that passive galaxies exhibit stronger spatial correlation than active galaxies at small scales (r <20 Mpc/h). The mark connection function, introduced here, is particularly useful for understanding the spatial correlation between the marks.