A little FABLE: exploring AGN feedback in dwarf galaxies with cosmological simulations

Abstract

Contrary to the standard lore, there is mounting observational evidence that feedback from active galactic nuclei (AGN) may also play a role at the low-mass end of the galaxy population. We investigate this using the cosmological simulation suite fable, with a particular focus on the dwarf regime (Mstellar < 109.5 M⊙). We find that overmassive black holes (BHs), with respect to the mean scaling relations with their host galaxies, drive hotter and faster outflows and lead to significantly reduced gas mass fractions. They are also more likely to display a kinematically misaligned ionized gas component in our mock MaNGA velocity maps, although we caution that cosmic inflows and mergers contribute to misalignments as well. While in the local Universe the majority of AGN in dwarfs are much dimmer than the stellar component, for z ≥ 2 there is a significant population that outshines their hosts. These high-redshift overmassive BHs contribute to the quenching of dwarfs, whereas at late cosmic times supernova (SN) feedback is more efficient. While our results are overall in good agreement with X-ray observations of AGN in dwarfs, the lack of high-luminosity X-ray AGN in fable at low redshifts highlights an interesting possibility that SN feedback could be too strong in fable’s dwarfs, curtailing AGN growth and feedback. We predict that future observations may uncover many more AGN in dwarfs with lower luminosities and at higher redshifts.

Merger Histories and Environments of Dwarf AGN in IllustrisTNG

“…Similarly, a lower stellar mass limit of 10 9 M is also used to resem- The copper 2D histogram shows TNG100-1 galaxies ble large scale observational surveys where this the effective mass limit (see e.g Kristensen et al 2020, Figure 11 for a mass distribution of local SDSS dwarf galaxies) and to ensure well resolved galaxies. This is in line with other studies on dwarf galaxies in simulations (Sharma et al 2020;Fattahi et al 2020;Dickey et al 2021;Koudmani et al 2021;Reddish et al 2021;Jahn et al 2021). These requirements can be summarised as follows:…”

“…The reasoning behind requiring a black hole is due to large number of dwarf galaxies with no black holes (N = 1 001, assuming same requirements for regular dwarf galaxies except M BH = 0 M ). This requirement is also used in other studies (e.g Koudmani et al 2021). For these galaxies' real life counterparts, there is no reason to assume they should not have a black hole as seeding mechanisms are still very unconstrained.…”

The black hole population in low-mass galaxies in large-scale cosmological simulations

“…These simulations include a physical BH formation model mimicking the PopIII remnant and compact stellar cluster models. The AGN occupation fraction was investigated in the FABLE cosmological simulation (whose BH seeding model does not follow one of the theoretical models) down to z = 0 in Koudmani, Henden & Sijacki (2021). Recently, a model for the AGN occupation fraction was derived in Pacucci, Mezcua & Regan (2021), based on gas properties and angular momentum of galaxies and calibrated against the X-ray AGN occupation fractions.…”

SDSS-IV MaNGA : spatial resolved properties of kinematically misaligned galaxies

“…In the last decades, several formation scenarios of gas-star misalignments have been proposed, including external gas accretion from dwarf companions as well as cosmic webs (Thakar & Ryden 1998;Chen et al 2016;Jin et al 2016), minor/major mergers (Naab et al 2014;Li et al 2020). Recent simulations (Starkenburg et al 2019;Duckworth et al 2020c;Koudmani et al 2021) find a higher incidence of AGN in misaligned galaxies, suggesting AGN feedback also plays a role in the formation of misalignment.…”

“…And the misaligned phenomenon is prevalence in 'red geysers'. Based on cosmological simulations, Starkenburg et al (2019), Duckworth et al (2020c and Koudmani et al (2021) investigated the impact of AGN feedback on the formation of low-mass misaligned galaxies, suggesting that low-mass misaligned galaxies tend to have increased AGN feedback and increased energy injection, which leads to the removal of pre-existing gas and further reduces the interaction between accreted and pre-existing gas, follow up external gas accretion leads to the gas-star misaligned phenomenon. In this work, we also find that the AGN fraction is 2-3 times higher in the SF and GV misaligned galaxies than their control samples, however, we would like to trust this as a nature result of gas inflow.…”