Exploring Galactic Scaling Relations with Numerical Simulations Claire Kopenhafer with Dr. Brian O’Shea Michigan State University, Dept. of Physics & Astronomy and Dept. of Computational Mathematics, Science, and Engineering

What usually people think of when they hear “galaxy”: What usually people think of when they hear “galaxy”: Disk of stars + gas

Circumgalactic Medium (gas) Bulge Disk Dark Matter Halo Not to scale; CGM radius is ~20 larger than the disk DM provides the gravitational potential (defines “out” and “in”)

Relationship of the Disk & CGM Outflows = feedback = SNe and AGN Hard to observe, unsure of specifics, but a good clue its important... c/o M. Peeples, STScI

Example of a Scaling Relation: Stellar Mass & Metallicity scaling relations = correlations between OBSERVABLE properties; notice how tight the relation is metals: metallicity = metal fraction; Metals come from stars, can trace where star stuff goes, change (cooling) properties of gas stellar mass scales with halo mass (not directly observable) 0.08 - 1 billion yrs ago 1.4 - 9 billion 2.5 - 11 billion (line styles - different methods for finding Z) Zahid et al. 2013, ApJ Letters, 771, L19

What is regulating feedback so that these scaling relations emerge? Scaling relations imply regulation Relationship between CGM & disk is a good candidate

Regulation via Precipitation “Cold” gas clouds precipitate out of the CGM, initiating star formation The largest of these stars result in supernovae, dumping energy and metals into the CGM The CGM inflates, lowering the density and increasing the cooling time of the gas Once the cooling time is long enough: precipitation stops star formation stops metal enrichment stops Voit et al. 2015 - analytic description of this process Stellar mass levels off over time as metals enter the CGM, slowing precipitation Explanation developed (primarily) by profs at MSU & their collaborators Cold is ~10,000 K for the MW Gas can also accrete on the central black hole, but AGN aren’t as important in MW sized halos (only larger) This process limits both the stellar mass and the metallicity (t_cool < 10 * t_ff; both cooling & t_ff affected by halo mass)

My Research: Testing the Analytic Predictions with Simulations In particular, reproduce MZR from Voit et al. (along with stellar baryon frac vs. max circular vel)

Kopenhafer et al., in prep Idealized, isolated galaxies Stars aren’t directly modeled Instead, gas is subtracted as if stars had formed Feedback occurs in defined regions (~3 million ly) 1 Mpc Simulation: cubic volume; dark matter halo What you’re seeing: projection of gas density; disk from the edge Full sim volume (why) & zoom in w/ feedback zones Left: full simulation volume Above: galactic disk over time Kopenhafer et al., in prep

A Different Approach Silvia et al., in prep So you get more of an idea of what I’m going for, & what the process looks like Temp Slices What to watch: center; start seeing some self-regulation That’s the goal for my sim; we’ve seen self-regulation develop in other sims from the group Silvia et al., in prep

Summary There are tight correlations between observable galaxy properties These relationships imply self-regulation mechanism(s) Precipitation is one possible mechanism I’m using simulations to test precipitation’s plausibility Importantly, the scaling relations all relate back to the halo mass We’ve talked about precip regulating stellar mass & metallicity (but it will also work for others - PAPER) Specifically, I’m testing in the context of MZR (+ one other but that’s not relevant rn)