Alignment between Luminous Red Galaxies and surrounding structures at $z\sim ~0.5$

Abstract

We analyse a high redshift sample ($0.4<z<0.5$) of LRG's extracted from the Sloan Digital Sky Survey Data Release 4 and their surrounding structures to explore the presence of alignment effects of these bright galaxies with neighbor objects. In order to avoid projection effects we compute photometric redshifts for galaxies within $3~\mpc$ in projection of LRGs and calculate the relative angle between the LRG major axis and the direction to neighbors within 1000 km/s. We find a clear signal of alignment between LRG orientations and the distribution of galaxies within $1.5\mpc$. The alignment effects are present only for the red population of tracers, LRG orientation is uncorrelated to the blue population of neighbor galaxies. These results add evidence to the alignment effects between primaries and satellites detected at low redshifts. We conclude that such alignments were already present at $z\sim 0.5$