Affiliation: University of Southampton

Contribution: Oral

Title: Self-Consistently Modelling Galaxy-Supermassive Black Hole Coevolution from z = 0–6

Abstract: The unprecedented view of the universe prior to cosmic noon facilitated by JWST challenges our understanding of galaxy evolution. Among the most unexpected discoveries are the Little Red Dots (LRDs), a population of active galactic nuclei (AGN) at z~4-6. These LRDs are over-massive with respect to local scaling relations, display a compact morphology, and are weak in the X-ray regime – possibly intrinsically so – but lie approximately an order of magnitude above the bolometric luminosity function. Another notable discovery is the population of massive, quenched galaxies observed 3<z<4. Here, we present a new, flexible approach, based on methodology of a semi-empirical model (SEM) but with some assumptions as in a semi-analytic model (SAM). This method reduces the number of free parameters by using abundance matching, while treating supermassive black hole (BH) growth in a more analytic manner. This approach enables the investigation of BH growth from z=6 to z=0, facilitating the investigation of the BH population at z=5, which can be compared to the LRDs, and exploring the link between BH growth, galaxy growth, and halo growth, which could constrain quenching via AGN feedback. In our model, galaxy growth is associated with the growth of their host dark matter (DM) halos through abundance matching between the specific halo accretion rate and the specific star formation rate. Central BHs within these galaxies are grown by sampling the observed Eddington ratio distribution function and integrating the accretion rates over cosmic time. Galaxy mergers are incorporated using the DM halo merger trees, assigning the stellar mass and BH mass at infall are assigned via the mean stellar mass – halo mass and stellar mass – BH mass relations, respectively. Quenching via AGN feedback is implemented by quenching the star formation and BH growth when a galaxy’s central BH mass surpasses a given galaxy – BH mass relation, under the assumption that the AGN driven wind is sufficient to expel the cold gas. We present results demonstrating the evolution of the BH mass function (BHMF) and the BH – galaxy scaling relations within this framework. We provide a detailed comparison of the BH demography at z=5 with the LRDs and infer the constraints under which the LRDs can naturally reproduce the local scaling relations, bolometric luminosity function, and BHMF. In addition, we analyse the contribution of BH quenching to the observed quenched fraction.

This contribution can be found here (pdf).