Astronomy and Astrophysics Seminars

Modeling the Formation and Evolution of Massive Galaxies in the Cosmos: Successes & Opportunities

by Dr. Arif Babul (University of Victoria)

Friday, June 2, 2023 from to (Asia/Kolkata)
at Hybrid ( A 269 ) Meeting ID: 946 5082 3821 Passcode: 599084
Over the past decade, there has been significant progress in modeling the formation and evolution of Milky-Way-like galaxies in the universe. Such galaxies, however, just the tip of the iceberg, so to speak. Put another way, they are the building blocks of cosmic structure, which includes massive galaxies, galaxy groups, clusters of galaxies. Holistic theories of galaxy formation ought to be able to, at the very least, explain, the properties of larger systems especially since these are directly impacted by galaxy scale properties. In this colloquium, I will discuss how well state-of-the-art cosmological structure simulations can account for the observed diversity in the properties of the massive galaxies, focusing on a subset of massive galaxies, the brightest group galaxies (BGGs). We use a high-resolution cosmological suite of simulations based on the Romulus model, and compare simulated central galaxies in group-scale halos at 𝑧 = 0 to observed systems. Since most galaxy formation models are calibrated using measures that are strongly influenced by the properties and evolution of “normal” Milky-Way like galaxies, this exercise is also an opportunity to test the limits of these models. We find Romulus BGGs that are early-type S0 and elliptical galaxies as well as late-type disk galaxies; we find Romulus BGGs that are fast-rotators as well as slow-rotators; and we observe galaxies transforming from late-type to early-type following strong dynamical interactions with satellites. In short, we find that Romulus reproduces the full spectrum of diversity in the properties of the BGGs very well. However, we also find a tendency towards lower than the observed fraction of quenched BGGs, with increasing halo mass, and the problem appears to be due to decreasing effectiveness of AGN feedback with increasing halo mass. Examining some of the other galaxy formation models, we find that they too run into trouble on the same scale — but in an opposite way. I will conclude by discussing what we are to make of this and what the path forward looks like.
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