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Scaling Relations of Spheroids over Cosmic Time: Tommaso Treu (UCSB)

Explore the cosmic evolution of stars, dark matter, and supermassive black holes in spheroids using scaling laws and empirical correlations. Investigate the compatibility of downsizing star formation with hierarchical models and examine the connection between black hole mass and spheroids. Discuss the challenges in resolving the size and velocity dispersion of distant objects and propose solutions using reverberation mapping and photo-ionization methods. Study the black hole mass vs. sigma relation and explore the recent evolution of bulges.

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Scaling Relations of Spheroids over Cosmic Time: Tommaso Treu (UCSB)

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  1. Scaling relations of spheroids over cosmic time: Tommaso Treu (UCSB)

  2. Outline • Use scaling laws (e.g. Fundamental Plane, M-sigma relation) to map the cosmic evolution of the three main constituents of spheroids: • Stars • Dark matter • Supermassive black holes

  3. 1: Stars Treu et al. 1999,2001,2002,2005a,b See di Serego Alighieri & van der Wel’s talks

  4. The Fundamental Plane as a diagnostic of stellar populations • Empirical correlation between size, luminosity and velocity dispersion • Gives “effective M/L” at “effective mass” Dressler et al. 1987; Djorgovski & Davis 1987; Bender Burstein & Faber 1992; Jorgensen et al. 1996

  5. Evolution of Mass to Light ratios • Evolution of mass to light ratio is a function of dynamical mass • More massive galaxies evolve slower than less massive ones, i.e. older stars (“downsizing”) Treu et al. 2005a

  6. Downsizing star formation Log M>11.5 11.5>Log M>11 11>Log M Young stars <1% Young stars ~5% Young stars up to 20-40% Treu et al. 2005b

  7. Stellar populations: conclusions • Stars in massive early-type galaxies are old • Stars in smaller galaxies are younger • Is this “downsizing” compatible with hierarchical models? • Perhaps, if massive galaxies are assembled without forming new stars (AGN feedback?) • But can other properties (e.g. dark halos, BH) be reproduced as well?

  8. 3: Supermassive Black Holes

  9. The local Universe Gebhardt et al. 2001; Tremaine et al. 2002 Ferrarese & Merritt 2001

  10. How do black-holes and spheroids know about each other? • The size of the dynamical sphere of influence of a BH is R~MBH7 / (σ200)2pc ~0.1-10 pc • The size of the spheroid is of order kpc • Typical accretion rates are of order 0.01 solar mass per yr for a 107 M_sun black hole. Mass of black holes could change over a Gyr timescale. • If spheroids evolve by mergers, what makes the BH and spheroids stay on the same correlation?

  11. The distant universe: two problems • Black hole mass: 1” at z=1 is ~8kpc. We CANNOT resolve the sphere of influence, active galaxies are the only option • Velocity dispersion: distant objects are faint and not resolved. If the galaxy is active we CANNOT avoid AGN contamination

  12. The distant universe: a solution, focus on Seyfert 1s • Black hole mass: • Reverberation mapping (Blandford & McKee 1982) does not need spatial resolution. • Empirically calibrated photo-ionization (ECPI: Wandel, Peterson & Malkan 1999) based on reverberation masses • Velocity dispersion: • integrated spectra have enough starlight that with good spectra it is possible to measure the width of stellar absorption features on the “featureless AGN continuum”. Treu, Malkan & Blandford 2004

  13. Measuring velocity dispersion. Woo, Treu, Malkan & Blandford 2006, astro-ph yesterday!

  14. Black-Hole Mass. Empirically Calibrated Photo-Ionization Method • The flux needed to ionize the broad line region scales as L(ion)/r2. Coefficients too hard to compute theoretically • An empirical correlation is found, calibrated using reverberation mapping Broad line region size L (5100AA) Wandel Peterson & Malkan 1999; Kaspi et al. 2000 Kaspi et al. 2005

  15. Black-Hole Mass. Hb width determination • Hb width from single epoch spectra provides a good estimate of the kinematics of the broad line region if constant narrow component is removed. (Vestergaard & Peterson 2006) • Overall uncertainty on BH mass ~0.4 dex

  16. The Black-Hole Mass vs Sigma relation at z=0.36 Woo, Treu, Malkan & Blandford 2006, astro-ph yesterday!

  17. The Black-Hole Mass vs Sigma relation at z=0.36; cosmic evolution? Δlog M BH redshift Δlog MBH = 0.62±0.10±0.25 dex

  18. Conclusions. • Bulges at z=0.36 smaller than their black-hole masses suggest. Three possibilities: • Selection effects • Problems with the ECPI method • Evolution

  19. Recent evolution of (active) bulges? Treu et al. 2006b

  20. Closing remarks: conjectures and predictions.. • Galaxies form initially as blue disks • Major mergers 1) trigger AGN activity, 2) quench star formation, 3) increase the bulge size • The characteristic mass scale decreases with time (‘downsizing’), consistent with that of our galaxies at z=0.36 Log Mtr redshift Hopkins et al. 2006 The M-sigma relation should be already in place for larger masses!

  21. The end

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