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

Sophie Koudmani,Debora Sijacki,Nicholas A Henden

doi:10.1093/mnras/stab677

Sophie Koudmani, Debora Sijacki + Show 1 more

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https://doi.org/10.1093/mnras/stab677

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Abstract

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 &lt; 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.

Highlights

In the ΛCDM model of structure formation, primordial density fluctuations grow and collapse into dark matter (DM) haloes
Though we note that any effect we find from active galactic nuclei (AGN) feedback in the low-mass regime is likely to be a lower limit
Focusing on the spatial distribution, there are low-mass galaxies with AGN in all types of cosmic environments: voids, filaments, and knots. This is in line with the observational findings from SDSS galaxies, which suggest that environment is not an important factor in triggering AGN activity in dwarf galaxies (Kristensen et al 2020)

Summary

Introduction

In the ΛCDM model of structure formation, primordial density fluctuations grow and collapse into dark matter (DM) haloes. The gas collapses within these haloes, cools and condenses to form stars. The dark and baryonic components build up together by accreting and merging with other structures. When comparing the DM halo mass function to the galaxy stellar mass function (GSMF), both the low-mass end and the high-mass end of the GSMF are found to be significantly suppressed. Feedback processes are usually invoked to explain this mismatch and to regulate the overall efficiency of star formation. In the common theoretical model, the low-mass end of the GSMF is suppressed by reionization Larson 1974; Dekel & Silk 1986; Mori et al 2002), whilst AGN feedback regulates the high-mass end In the common theoretical model, the low-mass end of the GSMF is suppressed by reionization (e.g. Efstathiou 1992; Okamoto et al 2008; Fitts et al 2017) and SN feedback (e.g. Larson 1974; Dekel & Silk 1986; Mori et al 2002), whilst AGN feedback regulates the high-mass end (e.g. Binney & Tabor 1995; Di Matteo et al 2005; Bower et al 2006; Croton 2006; Sijacki et al 2007; Cattaneo et al 2009)

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