Properties of galaxies and supermassive black holes in cosmic voids
Cosmic voids, the under-dense regions of the cosmic web, are widely used to extract cosmological information. Voids contain few, isolated galaxies, presumably expected to be less evolved and preserving memory of the pristine Universe. We use the cosmological hydrodynamical simulation Horizon-AGN coupled to the void finder VIDE to investigate properties of galaxies in cosmic voids at redshift z=0. We find that low-mass galaxies are more common than their massive counterparts at small void-centric distances. At fixed dark matter halo mass, they also have smaller stellar masses than in denser regions. While the star formation rate of void galaxies is lower when approaching the center of voids, their sSFR increases, suggesting that these void galaxies form stars more efficiently with respect to their stellar mass. We find that this can not only be attributed to the prevalence of low-mass galaxies. As a consequence of the presence of low-mass galaxies in voids, the inner regions of voids also predominantly host low-mass BHs. However, the ratios of BH mass to galaxy mass are similar to those of the whole simulation at z=0. Our results suggest that even if the growth channels in cosmic voids are different than in denser environments, voids grow their galaxies and BHs in a similar way. While a large fraction of the BHs have low Eddington ratios, we find that 20% could be observed as AGN with log10 L=41.5-42.5 erg/s in hard X-ray (2-10 keV). These results pave the way to future work with larger next-generation hydro simulations, aiming to confirm our findings and prepare the application on data from upcoming large surveys such as PFS, Euclid and WFIRST.