Effects of galaxy environment on merger fraction^⋆

¹ National Centre for Nuclear Research, Pasteura 7, 02-093 Warszawa, Poland
e-mail: william.pearson@ncbj.gov.pl
² Max Planck Institute for Extraterrestrial Physics, Gießenbachstraße 1, 85748 Garching, Germany
³ Institute of Astronomy, National Tsing Hua University, 101, Section 2. Kuang-Fu Road, Hsinchu 30013, Taiwan
⁴ Department of Space and Astronautical Science, Graduate University for Advanced Studies, SOKENDAI, Shonankokusaimura, Hayama, Miura District, Kanagawa 240-0193, Japan
⁵ Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, Kanagawa 252-5210, Japan
⁶ Research School of Astronomy and Astrophysics, The Australian National University, Canberra, ACT 2611, Australia
⁷ Centre for Astrophysics and Supercomputing, Swinburne University of Technology, PO Box 218 Hawthorn, VIC 3122, Australia
⁸ OzGrav: The Australian Research Council Centre of Excellence for Gravitational Wave Discovery, Hawthorn, VIC 3122, Australia
⁹ ASTRO3D: The Australian Research Council Centre of Excellence for All-sky Astrophysics in 3D, Canberra, ACT 2611, Australia
¹⁰ Astronomy Program, Department of Physics and Astronomy, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 08826, Republic of Korea
¹¹ SNU Astronomy Research Center, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 08826, Republic of Korea
¹² INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
¹³ School of Physical Sciences,The Open University, Walton Hall, Milton Keynes MK7 6AA, England, UK
¹⁴ Department of Earth Science Education, Kyungpook National University, 80 Daehak-ro, Buk-gu, Daegu 41566, Republic of Korea
¹⁵ Space Science and Technology Division, RALSpace, STFC Rutherford Appleton Laboratory, Chilton, Didcot OX11 0QX, England, UK

Received: 20 December 2023
Accepted: 15 March 2024

Abstract

Aims. In this work we examine how environment influences the merger fraction, from the low density field environment to higher density groups and clusters. We also study how the properties of a group or cluster, as well as the position of a galaxy in the group or cluster, influences the merger fraction.

Methods. We identified galaxy groups and clusters in the North Ecliptic Pole using a friends-of-friends algorithm and the local density. Once identified, we determined the central galaxies, group radii, velocity dispersions, and group masses of these groups and clusters. Merging systems were identified with a neural network as well as visually. With these identifications and properties of groups and clusters and merging galaxy identifications, we examined how the merger fraction changes as the local density changes for all galaxies as well as how the merger fraction changes as the properties of the groups or clusters change.

Results. We find that the merger fraction increases as local density increases and decreases as the velocity dispersion increases, as is often found in the literature. A decrease in merger fraction as the group mass increases is also found. We also find that groups with larger radii have higher merger fractions. The number of galaxies in a group does not influence the merger fraction.

Conclusions. The decrease in merger fraction as group mass increases is a result of the link between group mass and velocity dispersion. Hence, this decrease in merger fraction with increasing mass is a result of the decrease of merger fraction with velocity dispersion. The increasing relation between group radii and merger fraction may be a result of larger groups having smaller velocity dispersion at a larger distance from the centre or larger groups hosting smaller, infalling groups with more mergers. However, we do not find evidence of smaller groups having higher merger fractions.