The orientation of disk galaxies around large cosmic voids

TL;DR

This study analyzes the alignment of disk galaxies around large cosmic voids using SDSS data, finding significant alignment for larger voids and suggesting a link with dark matter halo orientations.

Contribution

It provides the first observational evidence of galaxy angular momentum alignment with voids and compares it with dark matter halo orientations from simulations.

Findings

Galaxies near large voids show significant alignment with the void's radial direction.

Alignment strength depends on the void's radius, diminishing for smaller voids.

The observed galaxy alignment is similar to dark matter halo orientations in simulations.

Abstract

Using a large sample of galaxies from the SDSS-DR7, we have analysed the alignment of disk galaxies around cosmic voids. We have constructed a complete sample of cosmic voids (devoid of galaxies brighter than M_r-5 log(h) =-20.17) with radii larger than 10 Mpc/h up to redshift 0.12. Disk galaxies in shells around these voids have been used to look for particular alignments between the angular momentum of the galaxies and the radial direction of the voids. We find that disk galaxies around voids larger than >~ 15 Mpc/h within distances not much larger than 5 Mpc/h from the surface of the voids present a significant tendency to have their angular momenta aligned with the void's radial direction with a significance >~ 98.8% against the null hypothesis. The strength of this alignment is dependent on the void's radius and for voids with ~<15 Mpc/h the distribution of the orientation of the galaxies is compatible with a random distribution. Finally, we find that this trend observed in the alignment of galaxies is similar to the one observed for the minor axis of dark matter halos around cosmic voids found in cosmological simulations, suggesting a possible link in the evolution of both components.