MaNGA AGN dwarf galaxies (MAD)

III. The role of mergers and environment in active galactic nucleus activity in dwarf galaxies

¹ Institute of Space Sciences (ICE, CSIC), Campus UAB, Carrer de Magrans s/n, 08193 Barcelona, Spain
² Institut d’Estudis Espacials de Catalunya (IEEC), Edifici RDIT, Campus UPC, 08860 Castelldefels (Barcelona), Spain
³ Instituto de Astrofísica de Canarias, Av. Vía Láctea s/n, E38205 La Laguna, Spain
⁴ Instituto de Física de Cantabria (IFCA, CSIC), Avda. de los Castros s/n, 39005 Santander, Spain

^⋆ Corresponding author: erostegui@ice.csic.es

Received: 5 March 2025
Accepted: 7 June 2025

Abstract

Context. Investigating whether and how galaxy mergers affect black hole growth can be a determinant for black hole-galaxy coevolution models and, in particular, for understanding how early Universe seed black holes grew to become supermassive. However, while mergers have been observed to enhance the active galactic nucleus (AGN) activity and thus black hole growth in massive galaxies, it is not yet known how this relation and the role of the environment translates to dwarf galaxies (the most likely hosts of the early seed black holes) since there are scarce and mixed results in the literature.

Aims. We seek to assess the impact of galaxy mergers and the environment on AGN triggering in dwarf galaxies.

Methods. We used a sample of 3280 dwarf galaxies with integral-field spectroscopic data from the MaNGA survey to study the AGN fraction throughout the merger process and how it is affected by the environment (characterized by galaxy isolation, being in a void, and group richness). We also compare the fraction of interacting galaxies in AGN and non-AGN dwarf galaxies.

Results. We find that dwarf galaxy mergers can ignite AGNs at separations below 20 kpc. The AGN fraction increases notoriously after the first pass and remains enhanced until the final stage. However, mergers are not the dominant AGN triggering mechanism. We also find that the environment has a non-negligible impact on AGN activity in dwarf galaxies, as the AGN fraction increases when moving to lower density environments. These findings provide the most statistically robust constraints to date on the effects of dwarf galaxy mergers and environment on AGN activity and black hole growth.