# Structure and dynamics in low density regions: galaxy-galaxy correlations inside cosmic voids

## TL;DR

This study analyzes the clustering and dynamics of faint galaxies within cosmic voids, revealing their mildly non-linear structure, low pairwise velocities, and environmental independence, supported by observational data and semi-analytic models.

## Contribution

It provides the first detailed analysis of galaxy correlations and velocities inside voids using SDSS data and semi-analytic models, highlighting their unique dynamical properties.

## Key findings

- Faint galaxies in voids show mildly non-linear clustering.
- Pairwise velocities of void galaxies are significantly lower than the global average.
- Void internal structure is environment-independent.

## Abstract

We compute the galaxy-galaxy correlation function of low-luminosity SDSS-DR7 galaxies $(-20 < M_{\rm r} - 5\log_{10}(h) < -18)$ inside cosmic voids identified in a volume limited sample of galaxies at $z=0.085$. To identify voids, we use bright galaxies with $M_{\rm r} - 5\log_{10}(h) < -20.0$. We find that structure in voids as traced by faint galaxies is mildly non-linear as compared with the general population of galaxies with similar luminosities. This implies a redshift-space correlation function with a similar shape than the real-space correlation albeit a normalization factor. The redshift space distortions of void galaxies allow to calculate pairwise velocity distributions which are consistent with an exponential model with a pairwise velocity dispersion of $w \sim 50-70$ km/s, significantly lower than the global value of $w \sim 500$ km/s. We also find that the internal structure of voids as traced by faint galaxies is independent of void environment, namely the correlation functions of galaxies residing in void-in-void or void-in-shell regions are identical within uncertainties. We have tested all our results with the semi-analytic catalogue MDPL2-\textsc{Sag} finding a suitable agreement with the observations in all topics studied.