SPS Seminar - The role of halo assembly history on black hole growth, circumgalactic gas expulsion, and the evolution of (simulated) ~L* galaxies

When:  Thursday 21^st January at 14.00

Where:  Microsoft Teams - Online

Speaker:  Rob Crain - Liverpool John Moores University

Hosted by: Hugh Dickinson

Abstract:

Galaxy formation models posit that the growth of massive galaxies is regulated, and even quenched, by energy liberated as gas accretes onto supermassive black holes (BHs) at their centres. We analyse the EAGLE and IllustrisTNG cosmological simulations to show that a fundamental
(but largely overlooked) step in the quenching of central galaxies is the efficient expulsion of a significant fraction of the circumgalactic medium (CGM), the reservoir of diffuse gas that envelops galaxies. It is notable that the simulations concur, because they adopt different assumptions about, and implementations of, the coupling of the energy liberated by BHs to interstellar gas. The simulations also concur that CGM expulsion is more efficient in early-assembling dark matter haloes
(at fixed halo mass), because their central galaxies develop more massive BHs than later-forming counterparts. However, the simulations yield dissimilar scaling relations between the properties of BHs and the CGM, potentially affording an effective route to constrain observationally the influence of BHs on the evolution of their host.

We isolate the influence of halo assembly from related variables (e.g. large-scale environment) using simulations of an individual present-day star-forming disc galaxy, whose initial conditions have been
"genetically" modified to enable controlled adjustment of its assembly history. These show convincingly that accelerating assembly generally leads to simulated galaxies quenching and evolving towards a more elliptical morphology, whilst delayed assembly leads to more vigorous
present day star formation rates.