The Spatial Range of Conformity

Abstract

Properties of galaxies like their absolute magnitude and their stellar mass content are correlated. These correlations are tighter for close pairs of galaxies, which is called galactic conformity. In hierarchical structure formation scenarios, galaxies form within dark matter halos. To explain the amplitude and the spatial range of galactic conformity two--halo terms or assembly bias become important. With the scale dependent correlation coefficients the amplitude and the spatial range of conformity are determined from galaxy and halo samples. The scale dependent correlation coefficients are introduced as a new descriptive statistic to quantify the correlations between properties of galaxies or halos, depending on the distances to other galaxies or halos. These scale dependent correlation coefficients can be applied to the galaxy distribution directly. Neither a splitting of the sample into subsamples, nor an a priori clustering is needed. This new descriptive statistic is applied to galaxy catalogues derived from the Sloan Digital Sky Survey III and to halo catalogues from the MultiDark simulations. In the galaxy sample the correlations between absolute Magnitude, velocity dispersion, ellipticity, and stellar mass content are investigated. The correlations of mass, spin, and ellipticity are explored in the halo samples. Both for galaxies and halos a scale dependent conformity is confirmed. Moreover the scale dependent correlation coefficients reveal a signal of conformity out to 40Mpc and beyond. The halo and galaxy samples show a differing amplitude and range of conformity.

10 pages with 7 figures using aa.cls, added further discussion of systematic effects and an expanded introduction and abstract

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