How galaxies populate haloes in very low-density environments

An analysis of the halo occupation distribution in cosmic voids

¹ Instituto de Astronomía Teórica y Experimental, CONICET-UNC, Laprida 854, X5000BGR Córdoba, Argentina
e-mail: german.alfaro@unc.edu.ar
² Observatorio Astronómico de Córdoba, UNC, Laprida 854, X5000BGR Córdoba, Argentina

Received: 30 December 2019
Accepted: 9 April 2020

Abstract

Context. Evidence shows that properties of dark matter haloes may vary with large-scale environment. Studying the halo occupation distribution in cosmic voids makes it possible to obtain useful information that can shed light on the subject. The history of the formation of the haloes and galaxies residing in these regions is likely to differ from the global behaviour given their extreme environment.

Aims. Our goal is to characterise the halo occupation distribution in the interior of cosmic voids and compare with the general results to unveil the way galaxies populate haloes in simulated galaxy catalogues.

Methods. We used two publicly accessible simulated galaxy catalogues constructed with different methods: a semi-analytical model and a hydrodynamic simulation. In both cases, we identified cosmic voids, and we measured the halo occupation distribution inside these regions for different absolute magnitude thresholds. We compared these determinations with the overall results, and we studied the dependence of different characteristics of the voids. We also analysed the stellar content and the formation time of the haloes inside voids and confronted the general halo population results.

Results. Inside the voids, we find a significantly different halo occupation distribution with respect to the general results. This is present in all absolute magnitude ranges explored. We obtain no signs of variation related to void characteristics, indicating that the effects depend only on the density of the large-scale environment. Additionally, we find that the stellar-mass content also differs within voids that host haloes with less massive central galaxies (∼10%), as well as satellites with significantly lower stellar-mass content (∼30%). Finally, we find a slight difference between the formation times of the younger haloes in voids than the average population. These characteristics indicate that haloes populating voids have had a different formation history, inducing significant changes on the halo occupation distribution.