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.
Figure courtesy of F. Governato
(α)
FEEDBACK
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.
Feedback
Stellar e.g. winds from massive stars
Supernova
Black Hole e.g. AGN feedback
Depending on mass of galaxy, different sources have varying importance
*realistic= look like observed galaxies in basic properties
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?
13
MARVELous Dwarf VolumesCaptain Marvel
ElektraStorm
Rogue
COMPLETE
COMPLETE
• run with ChaNGa • mgas=1.4e3 Msun,
mstar=400Msun, mdark=6e3Msun
• Effective resolution (4096)3
COMPLETE
a.k.a 40 Thieves
COMPLETE
TOTAL # RESOLVED DWARFS = 64
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MARVELous DwarfsCaptain Marvel
ElektraStorm
Rogue
COMPLETE
COMPLETE
Cpt Marvel run encapsulating multiple subgrid models- 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
implementation from Tremmel+ 2015)
COMPLETECOMPLETE
TOTAL # RESOLVED DWARFS = 64
15
Justice League Dwarfs• run with ChaNGa • mstar=3.9e3 Msun,
mgas=8.1e3Msun, mdark=1.3e5Msun
• Effective resolution (3072)3
• 4 volumes containing a Milky-Way sized halo- Sandra, Ruth, Sonia, Elena
TOTAL # RESOLVED DWARFS = 101
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
We cover a wide range of SFHs
Cum
ulat
ive
SFH
We cover a wide range of SFHs
Cum
ulat
ive
SFH
25
Simulations can predict fraction of halos that remain dark till present day
Only ~20% of 107 solar mass halos actually host a galaxyMunshi, Brooks + submitted
26
~Atomic Cooling Limit
As lower masses are probed, fewer and fewer halos are occupied! The occupied halos have differently shaped cumulative SFHs!
Low mass end of SMHM is poorly constrained…
SatellitesCentrals
Scatter ~ 0.9 dex
Scatter ~ 0.1 dex
Munshi+ submitted 40 Thieves: vMC
Low mass end of SMHM is poorly constrained…
…regardless of subgrid physics
MARVEL + Justice League Dwarfs
H2 based SF SMBH physics Higher SN feedback
29
Single halo- single luminosity assumption breaks down at low mass end
scatter in stellar mass for a given halo mass scatter in halo mass for a given stellar mass
Dark halos and extremely low mass halos contribute significantly to scatter
With one star halos (green)
With dark halos (yellow)
Garrison-Kimmel et al. (2017)
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 satellitesMunshi+, 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
Munshi+ in prep
Newest FIRE results consistent with H2 run- ask Coral
Dif. SF physics predicts different faint end slope of mass function
Munshi+ in prep
Need observations to constrain models!
Low mass end is sensitive to subgrid physics
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.
Feedback
Stellar e.g. winds from massive stars
Supernova
Black Hole e.g. AGN feedback
Depending on mass of galaxy, different sources have varying importance
*realistic= look like observed galaxies in basic properties
Bellovary, Cleary, Munshi + in prep
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)
These MBHs are not AGNs; are not distinguishable from other X-ray sources
Bellovary, Cleary, Munshi + in prep
MBHs preferentially form in denser environments
They are not necessarily in the center of their halos!
Bellovary, Cleary, Munshi + in prep
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!
Most common MBH merger ratio is dwarf’s MBH + SMBH of the MW progenitor nearby
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
45
Talk Summary
Elektra
Storm
Rogue
Captain Marvel
Justice League
• Combination of Justice League dwarfs + MARVELous dwarfs = 165 high-res dwarfs
• Can study broad range of dwarf properties including SMHM, SFHs, MBHs, radial gradients, resolved SFHs
