The effect of local and large-scale environments on nuclear activity and star formation

¹ Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, 200030 Shanghai, PR China
e-mail: margudo@shao.ac.cn
² Universidad de Antofagasta, Unidad de Astronomía, Facultad Cs. Básicas, Av. U. de Antofagasta 02800, Antofagasta, Chile
³ Key Lab for Astrophysics, 200234 Shanghai, PR China
⁴ Institute for Astronomy, University of Edinburgh, Edinburgh EH9 3HJ, UK
⁵ Instituto de Astrofísica de Andalucía (CSIC) Apdo. 3004, 18080 Granada, Spain
⁶ Departamento de Física Teórica y del Cosmos, Universidad de Granada, 18071 Granada, Spain
⁷ Instituto Universitario Carlos I de Física Teórica y Computacional, Universidad de Granada, 18071 Granada, Spain
⁸ Center for Astronomy and Astrophysics, Shanghai Jiao Tong University, 200240 Shanghai, PR China
⁹ IFSA Collaborative Innovation Center, Shanghai Jiao Tong University, 200240 Shanghai, PR China

Received: 1 February 2016
Accepted: 17 May 2016

Abstract

Context. Active galactic nuclei (AGN) are one of the main drivers for the transition from star-forming disk to passive spheroidal galaxies, however, the role of large-scale environment versus one-on-one interactions in triggering different types of AGN is still uncertain. We present a statistical study of the prevalence of the nuclear activity in isolated galaxies and physically bound isolated pairs.

Aims. For the purpose of this study we considered optically and radio selected nuclear activity types. We aim to assess the effect of one-on-one interaction on the fraction of AGN and the role of their large-scale environment.

Methods. To study the effect of one-on-one interaction on the fraction of AGN in isolated galaxy pairs, we compare these AGN with a sample of isolated galaxies homogeneously selected under the same isolation criterion. We examine the effect of the large-scale environment by comparing isolated systems with control samples of single galaxies and galaxy pairs. We use the tidal strength parameter to quantify the effects of local and large-scale environments.

Results. In general we found no difference in the prevalence of optical AGN for the considered samples. For massive galaxies, the fraction of optical AGN in isolated galaxies is slightly higher than that in the control samples. Also, the fraction of passives in high mass isolated galaxies is smaller than in any other sample. Generally, there is no dependence on optical nuclear activity with local environment. On the other hand, we found evidence that radio AGN are strongly affected by the local environment.

Conclusions. The optical AGN phenomenon is related to cold gas accretion, while radio AGN are related to hot gas accretion. In this context, there is more cold gas, fuelling the central optical AGN, in isolated systems. Our results are in agreement with a scenario where cold gas accretion by secular evolution is the main driver of optical AGN, while hot gas accretion and one-on-one interactions are the main drivers of radio AGN activity.