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

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 largescale 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.

The dependence of mass and environment on the secular processes of AGNs in terms of morphology, colour, and specific star-formation rate

“…We refer to "mass triggered" or "environment triggered" when the AGN is mostly triggered by stellar mass or environment, respectively, in a population of isolated galaxies where AGN would not be triggered by recent galaxy interactions or mergers. With this work we are extending a previous study carried out by Argudo-Fernández et al (2016). They observed different trends depending on galaxy mass.…”

“…Accordingly, we try to identify the connections between AGN activity and the stellar mass and the large-scale environment (LSS) in a population of isolated galaxies, where AGN would not be triggered by recent galaxy interactions or mergers, and thus black hole growths by secular processes (Hirschmann et al 2013). In this work we extend a previous study carried out by Argudo-Fernández et al (2016) and we focus on isolated galaxies to investigate the effect of both, mass and environment, on the fraction of optical nuclear activity in isolated galaxies as a function of their morphology, colour, and sSFR. We selected galaxies in the the SDSS-based catalogue of isolated galaxies (SIG, Argudo-Fernández et al 2015b).…”

“…2.2, the classification of AGN based on BPT diagrams is not perfect and there might be some issues to take into consideration. The obtained results, in comparison to Argudo-Fernández et al (2016), show that a separation between quenched and star-forming galaxies in terms of the sSFR provides a clean selection of SFN and AGN galaxy populations, since some star-forming galaxies could be classified as AGNs using BPT diagrams. Note also the sensitivity of the stellar mass cut log(M ) = 10.6 [M ] on the fraction of AGN in terms of sSFR when separating between low-mass and high-mass galaxies (see Appendix B for results using other stellar mass cuts).…”

“…With except to low-mass star-forming galaxies, where the fraction increases with higher Q LSS , the fractions of SFN are independent of the LSS. Therefore, even when exploring the trends observed in Argudo-Fernández et al (2016) in terms of morphology, colour, and sSFR, we still do not observe an increment of the SFN in void galaxies (here SIG galaxies with low values of the Q LSS ), as reported in Liu et al (2015). The difference between the results of the two studies may be therefore caused by the fact that the void population of galaxies are composed of galaxies with diverse local environments, commonly known as field galaxies, which may be composed of pairs and small groups of galaxies, where the spectral properties may be different and be affected by the group environment and/or interactions.…”

Probing the merger history of red early-type galaxies with their faint stellar substructures

“…Naab et al 2007), although direct gas accretion from cold streams, as inferred from numerical simulations and, very likely, from observations (e.g. Argudo-Fernandez et al 2016), may also play a key role in the building of galaxy disks.…”