Galaxy Assembly in a Hierarchical Universe

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Feedback from AGN during Galaxy Mergers
T. J. Cox
Phil Hopkins Lars Hernquist many others (the
Hernquist Mafia)
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projected stellar distribution
projected gas distribution
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Generic Outcome of Gas-Rich Galaxy Mergers

• Tidal torques ? large, rapid gas inflows (e.g.,
  Barnes Hernquist 1991)
• Triggers starburst (e.g., Mihos Hernquist 1996)
• Feeds BH growth (e.g., Di Matteo et al. 2005)
• BH Feedback disperses gas and reveals optical QSO
• Merging stellar disks grow spheroid
• Requires
• Major (?31) merger
• supply of cold (i.e., rotationally supported) gas

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Proposed Chronology of a Galaxy Merger
Cox et al. (2006)
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(No Transcript)
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Types of Feedback During Gas-Rich Galaxy Mergers
1. Merger/Gravitational Feedback collisional
heating of gas owing to the interaction
itself 2. Star Formation Feedback energy/mass
input from high-mass stars 3. QSO Feedback
energy input from high Eddington rate BH
accretion. Note that this is separate from, but
a necessary precursor to, Radio-mode feedback.
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Feedback from Star Formation and Black Holes

• Basic energetics suggest that Efb,SN Efb,BH
• Timescale for energy injection is NOT equivalent
  ?SP lt ?SF
• ? The power can be very different
• Location of energy injection is different quasar
  feedback is deposited in the galactic center,
  star formation feedback is spread throughout the
  galactic disk

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Relative Feedback During Active Phase

• gt5x more feedback energy from the BH

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Relative Feedback During Active Phase

• BH feedback during the active phase
  becomes increasingly dominant for systems of
  larger (total) mass

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BH Feedback During Active Phase

• BH feedback during the active phase
  regulates the mass of the black hole, and leads
  to the MBH-? relation.

Di Matteo et al. (2005), Springel et al. (2005)
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BH Feedback During Active Phase

• BH feedback during the active phase
  regulates the mass of the black hole, and leads
  to the MBH-? relation.

The tight scatter in the MBH- The BH
fundamental plane (the BH mass is fundamentally
related to the bulge binding energy)
Hopkins et al. (2007)
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Which Feedback Influences the Structure of Merger
Remnants?

• Stellar feedback!
• (it regulates the conversion of gas into stars
  and therefore determines the structure of the
  remnant galaxy)

w/ BH
w/o BH
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Color Evolution of Merger Remnants

• Star formation quenched by black hole feedback,
  remnant reddens quickly

Springel et al. (2004), Di Matteo et al. (2005)
with black hole
without black hole
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Color Evolution of Merger Remnants
Do we really NEED BH feedback to produce red
remnants? only for very
gas-rich mergers
moderate gas content (initially 40, nearly all
gas is consumed during merger)
high gas content (initially 100, a large amount
left after merger)
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• BH feedback likely regulates its own mass,
  but does it really need to be so violent (i.e.,
  lead to a massive superwind)?

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A Typical Galaxy Merger (take 2)
(on a larger scale)
projected gas distribution
Mass-weighted gas temperature
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The Influence on Gas in the Merger Remnant

• Significant coronae of hot gas is produced
• Mass and metals are ejected

explosion doesnt remove everything
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The Influence on Gas in the Merger Remnant

• Emits X-rays (consistent with E scaling
  relations)
• Cooling time and entropy are increased (Small
  systems may never cool and large systems are
  primed and ready for radio-mode feedback)
• but, SN-driven winds dominate the ejection of
  mass and metals

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Signatures of BH Feedback?

• Outflows visible in absorption (Christys talk
  yesterday)
• CO spectra (Appleton et al. 2002, Narayanan et
  al. 2006, Iono et al. 2007)
• SZ (Evans talk?)

Narayanan et al. (2006)
Tremonti et al. (2006)
NGC 6240 (Iono, et al., 2007, see also Appleton,
et al. 2002 in NGC 985)
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Conclusions

• Star Formation Feedback
• energy/mass input from high-mass stars
• dominant source of feedback, regulates star
  formation galaxy properties
• very likely to dominate the integrated mass
  and metal ejection

• QSO Feedback energy input from high Eddington
  rate BH accretion. Note that this is separate
  from, but a necessary precursor to, Radio-mode
  feedback.
• very brief, but powerful
• regulates black hole mass
• contributes to heating of remaining gas
• contributes to metal ejection
• contributes to color evolution in massive,
  high gas content mergers