Transcript Radial Profiles of Star Formation in the Far Outer Regions

A bit of (my) history
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My main PhD simulations
were performed on
COSMOS Mk I in 1998-99!
32 R10000, 8 GB of
memory, $2,000,000
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0.5×106 particles, only 4,000
timesteps
Simulations I’ll talk about
today, 32 core servers, with
64 GB, $20,000
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2.5×106 particles, but ×10
timesteps
AGN feedback modelling:
a comparison of methods
(a work in progress)
Rob Thacker
Associate Professor
& Canada Research Chair
Saint Mary’s University, Canada
Credit where a lot of credit is due
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This work is part of PhD student James
Wurster’s thesis
Outline
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Motivation
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Methods
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Physics issues, obs vs theory
Difficult choices to make, complicating factors
Problem(s) and resolution(s)
Our results
Conclusions
In a PhD thesis, far, far away….
Motivation
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Obs. evidence of AGN feedback has been
noted for years
Is the observational case compelling?
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Schawinski et al 2007, Fabian review
(arXiv:1204.4114)
Large ellipticals case is pretty good
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Radio mode commonly observed
Still need to understand situation in intermediate
masses, plus redshifts
Feedback Terminology
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Radio mode
Accreting hot gas
Sub-Eddington
luminosity
Radiatively inefficient
accretion
Radio jets provide
heat source
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Quasar mode
Accreting cold gas
Up to Eddington
luminosity
Radiatively efficient
accretion disk
Why compare?
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Comparison studies:
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1999 Santa Barbara cluster comparison
2006 Radiative transfer comparison
2011 Aquila galaxy formation comparison
Don’t give any real “answers”
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But do provide estimates of variation between
methods
=> “Be careful” about results until 3 groups agree
on it 
Remember…
“The 9 orders of magnitude in
The Optimistic
physical scale means
that all such Numericists view:
simulations include subgrid
assumptions and approximations.”
- Andy Fabian
Can we be “unwrong”
enough to give good insight?
Some thoughts to ponder…
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Timescale between onset of nuclear inflow
and AGN activity ~ 108 yrs
Many dynamical signatures evolve signifcantly
on that time scale
ALMA + JWST will be an enormous help
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Simultaneous SFRs, mass inflow rates,
understanding radiative behaviour
Good reasons to be optimistic
Prototype
merger
Merger movie
Four base models + one extra
But plenty of other work is related:
High res simulations of individual BH
Springel, di Matteo,
evolution/small scaleOkamato,
accretion Nemmen &
Hernquist 2005
Bower 2008
(SDH05) e.g. Levine et al 2008, 2010
(ONB08)
Alvarez, Wise & Abel 2009
Kim et al 2011
Hopkins & Quateart 2010
Booth & Schaye 2009
De Buhr, Quataret, & Ma
(BS09, slightly odd one
2011
Other “collision” work
out)
(DQM11)
e.g. Johansson, Naab & Burkert 2009
+WT2012
Halo
evolution
e.g. Sijacki et al 2009
Five key components
Model for BH
accretion rate
SPH particle
accretion algorithm
(Feedback) energy
return algorithm
Black hole advection
algorithm
Black hole merger
algorithm
Accretion physics
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Accretion of gas on to point in 1d: BondiHoyle-Lyttleton (1939,1944,1952)
- Gas density & sound speed at infinity
- Velocity of BH wrt to (distant) gas
Accretion physics II
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Maximal symmetric accretion rate is limited by
the Eddington rate
- Proton mass and Thompson X-section
- Efficiency of mass to energy conversion
Problems with BHL
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Physics:
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2d problem is known to produce unstable flow
Material inflow not radial – what about angular
momentum?
Radiative, magnetic effects etc
Numerics:
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How to relate physical variables to simulation
ones?
What additional variables to introduce for this?
What about angular momentum?
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Is the key physics
actually how material
reaches the black
hole?
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Gravitational torques
& viscosity keys?
Berkeley group
(Hopkins et al)
pursuing this
aggressively
Accreting SPH particles on to the
BH
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wi
wi
wi
Generic feedback physics
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E=mc2 makes life
easily
parameterizable, εr
Factor in efficiency of
energy coupling, εf
But is the impact
better modelled as
heating or
momentum?
+How to decide on sphere
of influence?
Heating approach (example)
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wi
wi
Note ONB08 apply heating to
halo gas directly!
Momentum approach
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Sphere of influence 4sft
Black hole advection
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Black hole advection is
trickier than you might
think
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Very important for accretion
calculation
N-body integrators
subject to 2-body effects
Want smooth advection
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Ideally toward potential
well bottom
Black hole advection – SDH05
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For low mass BH
(<10Mgas)
Find gas part. with lowest
PE
Relocate to that position if
vrel<0.25 cs
If BH starts to carve void
– can get problems
Black hole advection – ONB08
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Calculate local stellar density
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Follows local potential well
Move toward density
maximum
Step distance determined by
both velocity and softening
limit
Avoids significant 2-body
issues
Black hole merger algorithm
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Can give BH it’s own
smoothing length
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Or use grav softening
Merge when within certain
distance +
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When grav bound (e.g.
ONB08)
Or, when relative velocity
less than circ (e.g. BS09)
Summary of implemented models
Model
Accretion
model
SPH
accretion
Feedback
model
BH
advection
SDH05
BHL
Classic
probability
Heating
Lowest local Sound speed
PE
criterion
BS09
BHL+alpha
mod
Prob based
on mass
Heating
Lowest local
PE
Circular vel
criterion
DQM11
Viscous
timescale
Prob based
on mass
limit
Wind
Massive
tracer
Distance
only
ONB08
Drag based
Prob based
on mass
WT12
BHL
Local
particles
first
Halo heating Toward max
density
Heating
BH
merger
Grav bound
Toward max Sound speed
density
criterion
Numerical issues
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Some of these processes involve very small
cross-sections => numerically sensitive
Non-associativity of floating point has an
impact
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Worse in parallel comps – accumulations come in
different orders
We’re still quantifying the impact
Difficult decisions
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To vary star formation model or not to vary?
We’ve kept things the same – “classical”
model that’s pseudo-multiphase
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Modified cooling based upon pressure eqlb
between phases
Heated regions obvious in plots/movies
Can introduce some differences compared to
other researcher’s models (ask me at end)
Simulation models
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Classic two spiral
merger (very close to
Springel et al 2005
model)
End state: red & dead
elliptical
Low (~200k particles
per galaxy) and mid
(~1m) resolution
models
Movie 2
SFRs can be numerically sensitive
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SFRs are very numerically sensitive, from
Springel et al 2005:
If the star formation rate is tied to
gas density, the amplitudes of merger-induced starbursts depend
on the compressibility of the gas, which is influenced
by both the stiffness of the EOS, as well as dynamic range in
resolution of the numerical algorithm.
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Multiphase models suppress passage peak
Results – SFRs
Mid res
Initial peak from
disc response
SDH05
BS09
DQMe
DQM
ONB08
WT12
Low res
Disk morphology at apoapsis
Notice bar
mode less
strong
Movie 3
Results – black hole mass growth
M-σ for mid res final states
DQMe
DQM, SDH05, WT12
BS09
ONB08
Densities & temps “similar”
Results – time step
SDH05
BS09
ONB08
WT12
DQM
DQMe
Conclusions
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Very different behaviours – model
assumptions have enormous range
Interaction with SF very important
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Need to quantify degeneracies between model
parameters!
BH tracking is also quite resolution
dependent
AGN impact is far harder to model than SF
Thanks for the invite!
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Acknowledgements:
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NSERC
Canada Research Chairs Program
Canada Foundation for Innovation
Nova Scotia Research & Innovation Trust
Observational hope
Background
sources
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Duty cycle of AGN activity
Foreground
remains big unknown
AGN
Transverse proximity effect
(TPE) can measure it
Problems
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finding enough background
sources
30m class problem?
SF & AGN interaction
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Starburst-AGN connection well known
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SF impacts ISM around BH significantly
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Obs -> AGN peak activity about 0.5 Gyr after
starburst
Impacts temperature & accretion rates
How do these factors interplay?
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Not that well studied in simulations
Likely degeneracies between models