Baryon Cycles in the Biggest Galaxies

Michigan State University, East Lansing MI

Investigators

Abstract

In order to fully understand galaxy evolution one must identify the major processes that shape them over time. One such process is the “baryon cycle”, analogous to the Water and Carbon cycles on Earth, whereby gas cycles between a galaxy’s interstellar (ISM) and circum-galactic media (CGM) as determined by various heating (e.g., supernovae and radio jets) and cooling mechanisms, in the process forming a complex and dynamic galactic “atmosphere”. The details of this process regulates gas flows into or out of the galaxy and thus star formation and chemical enrichment of a galaxy’s environment. This research will use detailed numerical simulations to understand the dynamics of galactic atmospheres. The investigators will support public education through a dual-purpose website: one featuring visualizations of computer simulations and a second featuring interactive e-text to introduce students to the physics of galaxy atmospheres. One postdoc will be supported. This research will investigate the dynamics of galaxy atmospheres – i.e., the combined ISM and CGM – by determining its relaxed quasi-hydrostatic equilibrium states and the departures from these states due to energy input (e.g., supernovae and active galactic nuclei) and mass accretion. Three broad groups of numerical simulations will attempt to: (1) better understand how the condensation and subsequent “precipitation” of cool gas from the CGM to the ISM depends on (e.g.) the local gas turbulence, large-scale entropy gradients, perturbations, buoyancy, and the ratio of cooling and free-fall timescales; (2) make the first high spatial resolution study of the ability of narrow (opening angle < 10o) radio jets to indirectly suppress star formation in the ISM by heating the CGM and lowering the pressure and density of both on large scales. Gas from the galaxy ISM may be subsequently pushed into the CGM by supernovae; (3) better understand the ability of entropy gradients in the CGM produced by active galactic nuclei inflated “bubbles” to influence galaxy wide star formation, and how this process might depend on the galaxy’s halo mass (and the CGM’s “cosmological” entropy content). This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.