Supermassive Black Hole Growth from Cosmological N-body Simulations

Miroslav MicicKelly Holley-Bockelmann

Steinn SigurdssonTom Abel

Want more info? See astro-ph/0703540

Original goal: approach SMBH merger rates ‘from the opposite direction’ of EPS

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EPS-derived BH merger rates (per year)

• 0.1 – 100 Haehnelt 94

• 1 - 100 Menou et al 01

• 10 Sesana et al 04

• 15 - 350 Wyithe + Loeb 03

• 15 Rhook + Wyithe 05

How binary black holes meet and merge

O(10-5) pc

Galaxy merger BHs bound

O(106) pc

Dynamical friction

O(10) pc

3-body scattering Gravitational radiation

O(108) yr > O(1010) yr!** > O(1010) yr!*

*not anymore…thanks to excision and AMR

**in a static spherical galaxy with permanent ejections and no resonances

10 Mpc3 from z=40-0 with 2 Mpc refined sphere

Mlow = 5.6 x 107 M rlow=4 kpc N=2 x 106

Mhigh = 8.9 x 105 M rhigh=2 kpc N=5 x 106

The nuts and bolts:

Zooming into a group-sized volume of the universe

matter = 0.3 baryon= 0.045 dark energy = 0.7 n=1 8 = 0.9 h=0.7

Micic, HB, and Sigurdsson

Strategy: Pop III seeds and fast, efficient mergers

• identify all the halos at z=20, and seed those with M > few 107 M with

200 M BHs

• continue seeding new halos until z~12 (Pop III star formation squelched by UV background…)

• Trace the evolution of halos and their embedded BHs from z = 20-0.

• Assume that BHs merge once the halos merge.

• Explore three accretion schemes:

– Dry mergers only– Salpeter accretion excited by at least 4:1 mergers.– Salpeter accretion excited by M1:M2 < 10:1 mergers.

Sgr A*

M 31

Max black hole merger rate is ~ 55 per year

Low mass ratio, ~ 1000 M BH mergers most abundant overall

High mass ratio ~ 1000 M mergers dominate 2<z<6 ULXs?

Intermediate and Supermassive BH Growth

• BH merger rates ~55 per year

• Forming a 106 M SMBH requires major merger gas accretion

• To form a 107 M SMBH must also enlist gas accretion during minor mergers

• Largest SMBH is in place by z= 6, thereafter growth by mergers only (AGN era LISA era?)

• Lots of rogue IMBHs in a Milky Way-sized halo!

A gravitational wave implication

• ‘new’ IMBH-SMBH merger source with rates > O(10) per year

Next paper: Can LISA be used as a tool to constrain BH growth mechanisms?

…and a surprise: BH mass a product of environment

• a few isolated halos have extremely underweight bhs

Following the leads with better dynamics

• gravitational wave kicks!

• proper treatment of dynamical friction

How robust is this merger rate?

Explore rogue black hole dynamics within Milky Way halo

Smaller volume, better resolved simulation – 1 pc resolution with on the fly BH mergers

Smooth accretion – tidal disruption + capture and inspiral

Do those BHs in the isolated halos stay vastly underweight?

How does this relate to downsizing?

Cosmic variance -- several realizations of same volume (~105 CPU hrs)

Suppression mechanisms

Ho et al 2003

Spitballing: Is there a variable spread in M-sigma?

Largest SMBHs require ‘all’ accretion mechanisms + kicks inefficient (early growth)

IMBHs have many formation/growth channels+ kicks efficient