Complex Dynamics of Multiphase Gas in X-ray Cooling Cores

Abstract

This thesis investigates the dynamics of baryons in galaxy clusters, from hot X-ray atmospheres to stars, by connecting multi-wavelength observations across physical scales. I focus on the interplay between radiative cooling and radio-mechanical active galactic nuclei (AGN) feedback, which governs the dynamics of multiphase gas, and ultimately the evolution of cooling cores. First, I establish the large-scale thermodynamic conditions that govern cooling in cluster cores. Using the X-ray thermodynamic profiles of 85 groups and clusters, I quantify the differences between cool core and non-cool core systems, and study how they vary with radius. After accounting for mass-driven scatter, I demonstrate that cooling core signatures can be observed to a substantial fraction of R₂₅₀₀ (the radius within which the mean density is 2500 times that of the critical density), showing that these thermodynamic conditions are not simply constrained to the very central region where multiphase gas is observed, but are indeed well-established extended structures. This large-scale framework sets the stage for the detailed physical processes occurring on smaller scales. Next, I probe the complex dynamics of multiphase gas and stars in the central tens of kpc of four brightest cluster galaxies: Abell 1835, PKS 0745−191, Abell 262 and RX J0820.9+0752, using integral field spectroscopy obtained using the Keck Cosmic Web Imager. First, I map the distribution and kinematics of the warm ionized gas in these systems. In three of our four targets, the central galaxy and the nebular gas have a relative velocity of ∼150 km s⁻¹, revealing a dynamically active core environment where cooling and feedback proceed in a moving reference frame. In Abell 1835 and PKS 0745−191, I investigate how AGN feedback directly interacts with multiphase gas. Their nebular gas is composed of two kinematic components: an extended, quiescent phase and a churned-up component closer to the AGN that is disturbed by radio jets and cavities. Analysis of the churned-up phase reveals nebular gas outflows, leading to the first measurements of cavity velocities from nebular gas. The cavities' low speeds likely indicate mass-loading from uplifted gas, a process that can locally stimulate cooling. Finally, I connect these dynamics to stellar kinematics and star formation histories in three of the systems. This analysis further supports that AGN feedback can stimulate localized cooling and star formation. Abell 1835 and PKS 0745−191, both with strong AGN feedback, have extended recent star formation in their cores, while RX J0820.9+0752, with little AGN activity, lacks recent star formation. Most directly, in Abell 1835, I find tentative evidence that blueshifted young stars cooled out of a redshifted nebular outflow and are now infalling, supporting feedback-stimulated cooling and star formation. Together, this thesis links the larger-scale thermodynamic properties of the intracluster medium to the smaller-scale dynamics of multiphase gas and stars in cooling cores.