starburst efﬁciency and agn activity...impact on starburst efﬁciency • equal mass merger with...

Simulated galaxy merger trees:Starburst efficiency and AGN activity

Benjamin Moster (MPA)

Collaborators:Andrea Macciò, Rahul Kannan, Wouter Karman (MPIA),

Rachel Somerville (STScI), Thorsten Naab (MPA), T.J. Cox (Carnegie)

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• Employ pre-formed galaxy model

• Consists of: DM, gas, disc, bulge, BH

• Determine parameters:MDM, M*, fgas, rdisc, B/T, rmin, e, ...Chose parameters from grid

• Set on orbit and run systemuntil merger is complete

2 Benjamin Moster (MPA) Simulated galaxy merger trees Trieste, 05.04.2012

Galaxy Merger Simulations

• Pros: Cons:High resolution possible Huge parameter spaceVery quick (~days) No cosmological accretionPossible to test sub-grid Unclear what is typicalparameters

How to improve merger simulations?

• Add hot gas component in galactic halo

• Galaxy formation models predict large amount of hot gas in halo

• X-Ray observations (now) find emission from a cooling halo

• Expectation: hot halo cools and subsequently fuels cold disc! impact on starbursts & remnant morphology

• So far: merger simulations have mostly neglected the effects of a cooling hot halo


Extended Initial Conditions

• „Standard“ ICs with

i) Dark matter halo

ii) Bulge and BH

iii)Stellar and gaseous exponential discs

• Extend ICs with rotating hot halo

i) Use β-profile

ii) Adopt rc=0.22rs, β=2/3

iii)Hydrostatic equilibrium:

ρ(r) = ρ0

�1 +

�r

rc

�2�− 3

2β

T (r) =µmp

kB

1

ρhot(r)

� ∞

rρhot(r)

GM(r)

r2dr


Impact on starburst efficiency

• Equal mass merger with Mvir=1012Msun and 20% cold gas

• Maximum SFR is larger when hot gas is included

• SBE = mburst / mcold gas

• With hot halo:SBE is reduced

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• Remnant is less massive than galaxies in isolation

• Larger specific AM (by 25%)

• Higher temperature (by 70%) ! larger cooling time (by 35%)

Benjamin Moster (MPA) Simulated galaxy merger trees Trieste, 05.04.2012

Impact on starburst efficiency

• Equal mass merger with Mvir=1012Msun and 20% cold gas

• Maximum SFR is larger when hot gas is included

• SBE = mburst / mcold gas

• With hot halo:SBE is reduced

6

• Remnant is less massive than galaxies in isolation

• Larger specific AM (by 25%)

• Higher temperature (by 70%) ! larger cooling time (by 35%)

1

10

100

0 1 2 3 4 5

SFR

/ M

!yr

-1

t / Gyr

w/ hot halo, w/o BHw/ hot halo, w/ BH

0.001

0.01

0.1

1

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

BHAR

/ M

!yr

-1

t / Gyr


Quenching star formation?

• Equal mass merger with Mvir=3x1012Msun and 60% cold gas

• in/exclude hot gas and BHs

• No hot gas, with BH: star formation quenched

• No BH, with hot gas: SF can be sustained

• With BH and hot gas: SFR lowered after merger, but then increases again(refuelled cold gas comp.)

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0.1

1

10

100

1000

0 1 2 3 4 5

SFR

/ M

!yr

-1

t/Gyr

Isolated Runw/o hot halo, w/o BHw/ hot halo, w/o BHw/o hot halo, w/ BHw/ hot halo, w/ BH

0.0001

0.001

0.01

0.1

1

10

100

0 1 2 3 4 5

BHAR

/ M

!yr

-1

t/Gyr

w/o hot halo, w/ BHw/ hot halo, w/ BH

Coalescence


Can we further improve merger simulations?

• Merger simulations employ gas physics and have very high resolution (ideal to study galaxy evolution & morphology)

• But they lack cosmological context:When are the mergers? What properties do they have?

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• Use a SAM to predict general properties (ICs) of the merging galaxies:Stellar mass, gas fractions, B/T, orbits, etc...

• Use hydrodynamical simulations to evolve the mergers

• The small scale physics are treated in detailwhile the statistical properties are sampled well


• Extract merger trees from cosmological N-body simulations

Our Hybrid Approach

• Use SAM to derive the initial properties of main galaxy

• “Drop in” satellite using galaxy properties predicted by SAM, resume simulation

dark matterhot gascold gasstellar discstellar bulge

• Simulate main galaxy until 1st merger

• “Drop in” next satellite, repeat procedure for all satellites until z = 0

• Satellite orbits taken from N-body simulation

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black hole


our approach

NDM 6x106

N* 2x106

Ndisc 1.5x106

Res 100pc

T ~ 10 Gyr(z = 2 ! 0)

10 days~64 cores

Some interesting numbers

Can simulate statistical sample of galaxies

stars

gas

zoom-ins(Guedes+) 8x106

3x106

2x106

120pc

300 days>512 cores


Starbursts in simulated merger trees• Set of merger trees run and

analyzed by Wouter Karman

• Starting redshift z = 1.5

• Main haloes with Mvir=1-5x1012Msun

• Stellar mass agrees with abundance matching (Moster+10) for simulations with AGN feedback

• Runs with mergers often leadto less massive galaxiescompared to isolated runs

• Use simulation to parametrize starburst efficiency

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Abundance matching

Z = 0

Tree 990

Tree 872


Conclusions• We have extended the ICs to include the hot component

• Hot gas halo reduces starburst efficiency

• Mergers can lead to less massive galaxies wrt. isolated runs

• Hot gas can re-accrete after the merger! star formation even if SMBH is present

• We combine merger simulations and semi-analytic models:a) Cosmologically consistent initial conditionsb) High resolution to study galactic structure

• Study the dependance of the starburst efficiency on:merger mass ratio, gas fraction, bulge fraction, etc.


starburst efﬁciency and agn activity...impact on starburst efﬁciency • equal mass merger with...

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