Transcript Neistein_dekel60

Hydro simulations and SAMs:
two sides of the same coin
arXiv:1109.4635
Eyal Neistein
TMoX group, MPE Garching
Collaborators:
Sadegh Khochfar, Claudio Dalla-Vecchia, Joop Schaye
Eyal Neistein
Dekel 60
Hydrodynamic simulations (HYDs)
Typical questions:
• How each process affects the galaxy mass? (feedback, SF, Cooling)
• Why changing the parameters of a given process (e.g. SF) do not affect the
galaxies? What is `self-regulation’?
• What is the physics missing in order to reproduce the observational results
(e.g. the LF)?
• Can we extrapolate the results of one zoom simulation into a large volume
easily?
• Can we easily quantify the differences between different
codes/parameters?
We need a tool to post-process a HYD !
Eyal Neistein
Dekel 60
Semi-analytic models (SAMs)
Can we use a SAM in order to interpret HYDs?
What is a SAM?
• Each galaxy is described by only 3 numbers
• Use the same underlying DM merger trees as in the HYD
fs – star formation
fc – cooling;
fd – feedback
fa - accretion
Is this description accurate? Unique?
Do we need only hot & cold gas?
Is it the right tool ??
Eyal Neistein
Dekel 60
Project outline
1. We take a HYD that was run over a
cosmological box (OWLS, Schaye+10)
2. We extract the rates of: accretion,
cooling, feedback, and SF directly
from the HYD
3. We save these rates as function of halo
mass and redshift only
HYD
f  f (M , z)
4. We run our SAM using the above
recipes over the merger trees that are
extracted from the HYD
Recipes:
fs, fc, fd, fa
SAM
Dark matter
merger trees
Eyal Neistein
Dekel 60
The history of one galaxy
We follow all the particles, and check
which got heated/cooled/SF/accreted
fs – star formation
fc – cooling; fd – feedback
fa - accretion
Eyal Neistein
Dekel 60
How similar are the galaxies?
Galaxies are compared on an object-by-object basis:
The HYD & SAM are similar at a level of ~0.1 dex
Eyal Neistein
Dekel 60
Star-formation rates
The SFR includes more scatter than integrated
properties (like stellar mass)
Eyal Neistein
Dekel 60
Efficiency values
The HYD
physics is
different
from
typical
SAMs
Eyal Neistein
Dekel 60
One-phase model
Assume that each galaxy is composed
from ‘gas’ and ‘stars’ only:
Works well!!
Bouche +(2010), Krumholz & Dekel (2011); Khochfar & Silk (2011); Dave+ (2011)
Eyal Neistein
Dekel 60
SAM based on only one galaxy?
We chose 3 random galaxies from the box (
)
The SAM recipes are extracted from one galaxy only
The SAM runs over the entire volume
Works well!!
Eyal Neistein
Dekel 60
Summary
• HYD and SAM agree quite well, once efficiencies are matched on average
•
The SAM can be very simple, even one phase model is enough
•
All the recipes are summarized as a function of the host halo mass and redshift
•
The evolution of one galaxy includes enough information to extract the baryonic behavior
•
We have a common language for both SAMs & HYDs
Happy birthday Avishai !
Eyal Neistein
Dekel 60