AGN in dwarf galaxies: frequency, triggering processes and the plausibility of AGN feedback

Abstract

While AGN are considered to be key drivers of the evolution of massive galaxies, their potentially significant role in the dwarf-galaxy regime (M * < 10 9 M ⊙ ) remains largely unexplored. We combine optical and infrared data, from the Hyper Suprime-Cam (HSC) and the Wide-field Infrared Explorer (WISE) respectively, to explore the properties of ∼800 AGN in dwarfs at low redshift (z < 0.3). Infrared-selected AGN fractions are ∼10 -30 per cent in dwarfs, which, for reasonable duty cycles, indicates a high BH-occupation fraction. Visual inspection of the deep HSC images indicates that the merger fraction in dwarf AGN (∼6 per cent) shows no excess compared to a control sample of non-AGN, suggesting that the AGN-triggering processes are secular in nature. Energetic arguments indicate that, in both dwarfs and massive galaxies, bolometric AGN luminosities (L AGN ) are significantly greater than supernova luminosities (L SN ). L AGN /L SN is, in fact, higher in dwarfs, with predictions from simulations suggesting that this ratio only increases with redshift. Together with the potentially high BH-occupation fraction, this suggests that, if AGN feedback is an important driver of massive-galaxy evolution, the same is likely to be true in the dwarf regime, contrary to our classical thinking.

A binning-free method reveals a continuous relationship between galaxies’ AGN power and offset from main sequence

“…AGNs) ranges from a few per cent to a few tens of per cent, depending on galaxy mass (e.g. Kauffmann et al 2003;Best et al 2005;Mullaney et al 2012;Kaviraj, Martin & Silk 2019). What this implies is that an individual supermassive black hole (SMBH) spends most of cosmic time in a 'dormant' state during which it accretes at such a low rate as to make it unidentifiable as an AGN (e.g.…”

Galaxy morphological classification in deep-wide surveys via unsupervised machine learning

“…Finally, morphological details, such as extended tidal features, are signposts of recent mergers and/or strong interactions (e.g. Kaviraj 2014b; Kaviraj et al 2019), with the surfacebrightness of these tidal features typically scaling with the mass ratios of the mergers in question (e.g. Peirani et al 2010;Kaviraj 2010).…”

Eigengalaxies: describing galaxy morphology using principal components in image space

“…In a similar vein, morphological details such as extended tidal features suge.uzeirbegovic@herts.ac.uk gest recent mergers and/or interactions (e.g. Kaviraj 2014;Kaviraj et al 2019;Jackson et al 2019), with the surface brightness of these tidal features typically scaling with the mass ratios of the mergers in question (e.g. Peirani et al 2010;Kaviraj 2010).…”

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