The MARVELous Dwarfs meet the Justice League: Constraints on Dwarf Galaxies using a heroically large simulated sample Ferah Munshi VIDA Fellow, Vanderbilt University (—> Assistant Prof, OU this fall) In collaboration with: Alyson Brooks, Dan Weisz, Jillian Bellovary, Kelly Holley-Bockelmann , Elaad Applebaum, Charlotte Christensen+ UW N-body Shop* Email: [email protected] The Abundance of Dwarf Galaxies Ferah Munshi VIDA Fellow, Vanderbilt University (—> Assistant Prof, OU this fall) In collaboration with: Alyson Brooks, Dan Weisz, Jillian Bellovary, Kelly Holley-Bockelmann , Elaad Applebaum, Charlotte Christensen + UW N-body Shop* Email: [email protected] I use cosmological N- body + SPH galaxy simulations to figure out how galaxies form and evolve- i.e., how they come to look as they do today. What is a (N-body) Simulation? Modeling a dynamical system of particles, usually under the influence of physical forces, in this case: gravity For me: stars + dark matter, acting under the influence of gravity, within a galaxy What is an N-body + SPH Simulation? • SPH= “smoothed particle hydrodynamics” • computational method used for simulating fluid flows- ie, gas • Gas is divided into a set of discrete elements, referred to as “particles” • “cosmological”= from early times all the way to present day Galaxies are made up of stars, gas and dark matter (the majority of a galaxy is in dark matter) FEEDBACK can imprint its affects on all three components In dwarf galaxies, feedback is key in understanding the dark matter profiles. (α) FEEDBACK Figure courtesy of F. Governato Galaxies are made up of stars, gas and dark matter (the majority of a galaxy is in dark matter) FEEDBACK can imprint its affects on all three components In dwarf galaxies, feedback is key in understanding the dark matter profiles. How does feedback imprint itself on the other components? All feedback mechanisms have this in common: They heat gas, drive outflows, and suppress star formation In order to simulate a galaxy, you must be able to model feedback. Feedback is necessary to form realistic* galaxies. *realistic= look like observed galaxies in basic properties Stellar e.g. winds from massive stars Feedback Supernova Black Hole e.g. AGN feedback Depending on mass of galaxy, different sources have varying importance So how do you know you’re modeling feedback correctly? Compare to observations! Big question #1: How do feedback and star formation affect the stellar to halo mass relationship (SMHM)? What is the abundance and scatter of low mass galaxies? How do they populate their dark matter halos? MARVELous Dwarf Volumes Captain Marvel • run with ChaNGa a.k.a 40 Thieves • mgas=1.4e3 Msun, mstar=400Msun, mdark=6e3Msun 3 • Effective resolution (4096) COMPLETE TOTAL # RESOLVED DWARFS = 64 COMPLETE Rogue Storm Elektra COMPLETE COMPLETE 13 MARVELous Dwarfs Cpt Marvel run encapsulating multiple subgrid models- Captain Marvel 1. High density threshold SF (MC run) [formerly 40 Thieves] 2. H2 based SF (H2 run) [formerly 40 Thieves] 3. H2 based SF + “SM”BHs (BH COMPLETE implementation from Tremmel+ 2015) TOTAL # RESOLVED DWARFS = 64 COMPLETE Rogue Storm Elektra COMPLETE COMPLETE 14 Justice League Dwarfs • run with ChaNGa • 4 volumes containing a • mstar=3.9e3 Msun, Milky-Way sized halo- mgas=8.1e3Msun, Sandra, Ruth, Sonia, mdark=1.3e5Msun Elena • Effective resolution (3072)3 TOTAL # RESOLVED DWARFS = 101 15 MARVELous Dwarf Volumes + Justice League Dwarfs = 165 High-resolution simulated dwarfs Charm Nbody GrAvity solver • Massively parallel SPH (smoothed particle hydrodynamics); fully cosmological • SNe feedback creating realistic outflows • SF linked to shielded gas • Optimized SF parameters • NEW SPH implementation • Previous gen code: Gasoline Menon+ 2014, Governato+ 2014 z=0 DM density z=0 Gas density Sandra: highest simulated redshift —> present day Mass-Metallicity matches observations Mass-Metallicity matches observations Star Formation consistent with local dwarfs Cumulative SFH We cover a wide range of SFHs Cumulative SFH We cover a wide range of SFHs Simulations can predict fraction of halos that remain dark till present day Only ~20% of 107 solar mass halos actually host a galaxy Munshi, Brooks + submitted25 ~Atomic Cooling Limit As lower masses are probed, fewer and fewer halos are occupied! The occupied halos have differently shaped cumulative SFHs!26 Low mass end of SMHM is poorly constrained… Scatter ~ 0.1 dex Scatter ~ 0.9 dex Satellites Centrals Munshi+ submitted 40 Thieves: vMC Low mass end of SMHM is poorly constrained… MARVEL + Justice League Dwarfs H2 based SF SMBH physics Higher SN feedback …regardless of subgrid physics Single halo- single luminosity assumption breaks down at low mass end 29 Dark halos and extremely low mass halos contribute significantly to scatter scatter in stellar mass for a given halo mass scatter in halo mass for a given stellar mass Garrison-Kimmel et al. (2017) With one star halos (green) With dark halos (yellow) Munshi+ 2017 The scatter has observational ramifications for the stellar mass function In essence, Munshi+ 2017 is a *tool* to populate low mass halos stochastically, in order to make predictions Munshi+ 2017 Two runs, same initial conditions, different SF/ Feedback prescription -predict similar satellite mass functions However… Munshi+, in prep They predict vastly differing numbers of luminous satellites Munshi+, in prep What’s the difference? Conditions of gas where stars are forming (density!) Munshi+, in prep, Christensen+ 2012 Dif. SF physics predicts different frequencies of dwarf satellites in LG Newest FIRE results consistent with H2 run- ask Coral Munshi+ in prep Dif. SF physics predicts different faint end slope of mass function Low mass end is sensitive to subgrid physics Need observations to constrain models! Munshi+ in prep Summary • Abundance of dwarf galaxies is largely unconstrained- abundance matching breaks down here! • Simulations, like MARVEL + Justice League, can begin to constrain fraction of populated galaxies and the scatter • BUT! the physics of your simulation changes your predictions- we have to be very careful Munshi+ 2017 Feedback is necessary to form realistic* galaxies. *realistic= look like observed galaxies in basic properties Stellar e.g. winds from massive stars Feedback Supernova Black Hole e.g. AGN feedback Depending on mass of galaxy, different sources have varying importance Stars are dwarfs which host a MBH Bellovary, Cleary, Munshi + in prep • MBH seeds form via direct collapse • Probabilistic approach- similar conditions to SF • MBH formation prescription as in Tremmel+ 2015,2016 • MBHs form at high -z • Truncation due to propagation of metals (need pristine gas) • Formation halo mass as expected from models of direct collapse (e.g. Lodato & Natarajan 2006) (virialized halo gas reaches 104K) Bellovary, Cleary, Munshi + in prep These MBHs are not AGNs; are not distinguishable from other X-ray sources MBHs preferentially form in denser environments They are not necessarily in the center of their halos! Bellovary, Cleary, Munshi + in prep Most common MBH merger ratio is dwarf’s MBH + SMBH of the MW progenitor nearby MBH mergers happen at all z's. LISA will be sensitive to those at high-z. LISA is a way to probe structure formation at high-z through these MBH mergers! Bellovary, Cleary, Munshi + in prep Part 2 Summary • MBHs in dwarfs preferentially form in higher density environments • MBH mergers at high-z observed by LISA will be a tracer of early structure formation • MBHs are not active (now or in the past)- hard to observe in light Talk Summary • Combination of Justice League dwarfs + MARVELous dwarfs = 165 high-res dwarfs • Can study broad range of Captain Marvel dwarf properties including SMHM, SFHs, MBHs, radial gradients, resolved SFHs Justice League Elektra Rogue Storm 45.