Sociology and hierarchy of voids: A study of seven nearby CAVITY galaxy voids and their dynamical CosmicFlows-3 environment

¹ Université Claude Bernard Lyon 1, IUF, IP2I Lyon, 69622 Villeurbanne, France
e-mail: helene.courtois@univ-lyon1.fr
² Kapteyn Astronomical Institute, University of Groningen, PO Box 800 9700 AV Groningen, The Netherlands
³ IRFU, CEA Université Paris-Saclay, 91191 Gif-sur-Yvette, France
⁴ Departamento de Física Teórica y del Cosmos, Campus de Fuente Nueva, Edificio Mecenas, Universidad de Granada, 18071 Granada, Spain
⁵ Instituto Carlos I de Física Teórica y Computacional, Facultad de Ciencias, 18071 Granada, Spain
⁶ Institute of Space Sciences (ICE, CSIC), Campus UAB, Carrer de Can Magrans, s/n, 08193 Barcelona, Spain
⁷ Institut d’Estudis Espacials de Catalunya (IEEC), 08034 Barcelona, Spain
⁸ Instituto de Astrofísica de Andalucía – CSIC Glorieta de la Astronomía, 18008 Granada, Spain
⁹ Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstrasse 12-14, 69120 Heidelberg, Germany
¹⁰ National Astronomical Observatory of Japan, National Institutes of Natural Sciences, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
¹¹ Departamento de Astronomía y Astrofísica, Universidad de Valencia, c/ Dr. Moliner n 50, 46100 Burjassot, Valencia, Spain
¹² Observatori Astronémic, Universitat de València, 46980 Paterna, València, Spain
¹³ Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
¹⁴ Instituto de Astrofísica de Canarias, c/ Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
¹⁵ Institut de Radioastronomie Millimétrique (IRAM), Av. Divina Pastora 7, Local 20, 18012 Granada, Spain

Received: 29 November 2022
Accepted: 9 February 2023

Abstract

Context. The present study addresses a key question related to our understanding of the relation between void galaxies and their environment: the relationship between luminous and dark matter in and around voids.

Aims. To explore the extent to which local Universe voids are empty of matter, we study the full (dark+luminous) matter content of seven nearby cosmic voids that are fully contained within the CosmicFlows-3 volume.

Methods. We obtained the matter-density profiles of seven cosmic voids using two independent methods. These were built from the galaxy redshift space two-point correlation function in conjunction with peculiar velocity gradients from the CosmicFlows-3 dataset.

Results. The results are striking, because when the redshift survey is used, all voids show a radial positive gradient of galaxies, while based on the dynamical analysis, only three of these voids display a clear underdensity of matter in their center.

Conclusions. This work constitutes the most detailed observational analysis of voids conducted so far, and shows that void emptiness should be derived from dynamical information. From this limited study, the Hercules void appears to be the best candidate for a local Universe pure “pristine volume”, expanding in three directions with no dark matter located in that void.