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The W i d e s p r e a d Influence of Supermassive Black Holes

Explore the widespread impact of supermassive black holes in galaxies, from their gravitational effects to feeding mechanisms and merger signatures. Investigate AGNs and their role in galaxy evolution using reverberation mapping, surveys, and simulations.

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The W i d e s p r e a d Influence of Supermassive Black Holes

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  1. The W i d e s p r e a d Influence of Supermassive Black Holes Christopher Onken Herzberg Institute of Astrophysics

  2. The Milky Way • Sgr A* • Seen in X-rays, radio, IR • 3.5 Million M Optical image X-ray image (Chandra) Near-IR (HKL) image (VLT) Radio (6 cm) image (VLA)

  3. “S” Stars • Orbits followed for ~10 years Keck VLT

  4. Hypervelocity Stars • 7 Galactic stars with radial velocities of 400+ km/s • Ejected from Galactic Center • No proper motions yet, so velocities are lower limits

  5. 3-Body Interactions • Orbital energy is exchanged, ejecting one star at high speed • Remaining stars left in tighter orbit sverre.com

  6. Larger Connections • Tight correlation between SBH mass and galaxy velocity dispersion (M-) • Far beyond direct influence of SBH’s gravity Black hole mass  Stellar velocity 

  7. Star Clusters Instead of SBHs? • Some galaxies seem to have nuclear star clusters but may not have SBHs • Star clusters also seem to be correlated with galaxy properties (mass, in this case) Black hole mass or Cluster mass  Galaxy mass  Stellar velocity 

  8. Feeding the Monster • Active Galactic Nuclei (AGNs) • SBHs that are actively accreting matter • Among the most luminous objects in the universe • Highly variable

  9. Reverberation Mapping (an analogy) V838 Mon (HST imaging, 2002-2005)

  10. Reverberation Mapping • Take advantage of variability • Changes in ionizing radiation drive changes in emission lines • Measure V

  11. Reverberation Mapping • There is a time delay between variations in continuum and response of emission lines • Represents the travel time of the radiation from the SBH to the line-emitting gas • Time delay of 1 day = distance of 1 light-day

  12. AGN Masses • From measurements of velocity (line width) and distance (time lag), the SBH mass can be estimated • Different emission lines have different widths and lags, but give consistent SBH masses

  13. AGN M- Relation • AGNs consistent with inactive galaxy relation, but larger errorbars and larger scatter Black hole mass  Stellar velocity  AGNs Inactive Galaxies

  14. Shortcut to AGN Masses • Approximate line width measurement from a single spectrum • Estimate radius of line-emitting gas from one measurement of the continuum luminosity • AGN mass from a single spectrum! Time delay  Reverberation campaign AGN luminosity  Single spectrum

  15. Extending the M- Relation • A handful of low-mass AGNs have measured velocity dispersions • Appear to follow the inactive galaxy relation, but may show flattening of slope at low  Black hole mass  Stellar velocity 

  16. AGN Surveys Deep surveys of small area can find faint AGNs but miss the rare objects. AGN and Galaxy Evolution Survey (AGES) Black hole mass  MMT AGN Luminosity 

  17. AGN Surveys Large area surveys produce tens of thousands of AGN masses, probing most of the history of the universe. 2dF Quasar Redshift (2QZ) Survey Black hole mass  AAT AGN Luminosity 

  18. Putting the Pieces Together • Need to combine the information from different types of surveys to develop a complete picture of SBH growth • Still need to identify a mechanism for feeding the SBH

  19. Mergers? • Many AGNs appear to be in mid-collision • Number of AGNs has fallen over the last 10 billion years, roughly in line with declining merger rate of dark matter halos Dark blue: 2 massive galaxies Green: 2 massive SBHs Merger rate  Number of AGNs   Universe Age Universe Age 

  20. Merger Simulations • Model gas, stars, & dark matter • Use empirical relations to insert formation of new stars Produce too many big, blue galaxies--too many new stars formed because too much cold gas remains in the merged galaxy.

  21. SBHs as the Solution? • Add SBH to the model • Assume gas close to the SBH falls in (becomes an AGN) • Small amount of AGN energy (~5%) heats gas in the galaxy

  22. Simulation Predictions • 5% feedback efficiency chosen to match observed M- relation • Removal of gas by AGN cuts off star formation (no big blue galaxies) Red Blue Galaxy color Red Black hole mass  Blue Stellar velocity  Galaxy mass 

  23. Predicted AGN Activity • Provides a reasonable match to observed distribution of accretion rates AGES Predictions from a single merger simulation

  24. Is This Feedback Reasonable? • Jets and other outflows are seen in AGNs

  25. Too Strong? • Simulated jets blast through the surrounding gas and don’t input energy for very long

  26. But If It DOES Work… • AGN feedback could solve another problem: a lack of “warm” (106 K) gas in some galaxy clusters • Hot gas should be cooling, condensing onto the central galaxy, forming stars • AGN energy input could explain why that doesn’t occur X-rays: color, radio: contours

  27. Another Merger+SBH Signature? • Mergers could also explain flatter inner profile of massive galaxies • Mergers of roughly equal mass galaxies with SBHs flatten the central stellar density profile Density of stars  Galaxy radius 

  28. Progress Report • The last 10 years have seen significant developments in our understanding • Plenty of interesting questions remain • How are the first SBHs formed? • Are SBHs and star clusters related? • Can mergers explain everything? • Do galaxies really “explode”?

  29. Future Steps: Observations:Milky Way • Passage of time improves knowledge of “S” star orbits • Probing fainter stars with better angular resolution and deeper observations • More follow-up for hypervelocity stars

  30. Future Steps: Observations:Mass Measurements • Continuing observations of low-mass AGNs, nuclear star clusters • TMT will allow a large number of new SBH mass measurements Predicted SBH Mass  Distance from Sun 

  31. Future Steps: Observations:Reverberation Mapping • Recent campaign at MDM Observatory • 2-D reverberation mapping with Kronos MDM 1.3m Time delay  Time delay  Gas velocity  Gas velocity 

  32. Future Steps: Observations:AGN Surveys • SDSS (~80,000 AGNs, ~8,000 deg2, g<20.2) • 2SLAQ (~10,000 AGNs, g<21.8, ~400 deg2) with 2dF instrument on AAT 2dF SDSS Telescopes

  33. Future Steps: Simulations • Improved computing power will allow higher spatial & temporal resolutions • Include more detailed physics “Columbia” at NASA-Ames: 43 teraflops -2GHz Pentium 4: few gigaflops -Xbox 360: ~100 gigaflops

  34. Summary • SBHs reveal themselves by their extreme influence on their immediate surroundings • But recent evidence points to SBHs having important effects on larger size scales, impacting their host galaxies and even galaxy clusters

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