Letter to the Editor

A triple active galactic nucleus in the NGC 7733–7734 merging group

¹ Indian Institute of Astrophysics, Koramangala II Block, Bangalore 560034, India
e-mail: jyoti@iiap.res.in
² Pondicherry University, R.V. Nagar, Kalapet, 605014 Puducherry, India
³ Observatoire de Paris, LERMA, College de France, CNRS, PSL University, Sorbonne University, 75014 Paris, France

Received: 29 April 2021
Accepted: 22 June 2021

Abstract

Context. Galaxy interactions and mergers can lead to supermassive black hole (SMBH) binaries, which become active galactic nucleus (AGN) pairs when the SMBHs start accreting mass. If there is a third galaxy involved in the interaction, then a triple-AGN system can form.

Aims. Our goal is to investigate the nature of the nuclear emission from the galaxies in the interacting pair NGC 7733–NGC 7734 using archival VLT/MUSE integral field spectrograph data and study its relation to the stellar mass distribution traced by near-infrared (NIR) observations from the South African Astronomical Observatory (SAAO).

Methods. We conducted NIR observations using the SAAO and identified the morphological properties of bulges in each galaxy. We used MUSE data to obtain a set of ionized emission lines from each galaxy and studied the ionization mechanism. We also examined the relation of the galaxy pair with any nearby companions with far-ultraviolet observations using the UVIT.

Results. The emission line analysis from the central regions of NGC 7733 and NGC 7734 shows Seyfert and low ionization nuclear emission-line regions type AGN activity. The galaxy pair NGC 7733−34 also shows evidence of a third component, which has Seyfert-like emission. Hence, the galaxy pair NGC 7733−34 forms a triple-AGN system. We also detected an extended narrow-line region associated with the nucleus of NGC 7733.