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