The Build-up of Quasars

1. The Build-up of Quasars Gordon Richards Drexel University With thanks to Michael Strauss, YueShen (Princeton), Don Schneider, Nic Ross (Penn State), Adam Myers (Illinois), Phil Hopkins (Berkeley), and a host of other people from the SDSS Collaboration

2. Caveats I tend to be biased towards: • High redshift (z>1) • High luminosity • Optical Selection • “Quasar” mode accretion • Unobscured (i.e., type 1) • Quasar=QSO=AGN=any actively accreting supermassive black hole

3. The Redshift Desert • Redshift desert for galaxies due to lack of spectral features in the optical octave at z~2. • No redshift desert for quasars (in the galaxy sense), but there is in reality. And just as frustrating. Galaxy Franx 2003 Quasar

4. The z~2.7 Quasar Desert Observed Corrected Schneider et al. 2007

5. Z~2.7 Quasar Colors At 2.5<z<3.0 quasars cross through the locus of stars, making those quasars harder to identify (efficiently).

6. X-ray and IR Selection • X-ray and IR selection don’t suffer from the same problem (and they allow selection of obscured quasars). • But they do have their own problems. • Area surveyed by X-ray is tiny. • Mid-IR has its own 3.5<z<5 desert. • Not clear that optical/radio/MIR/X-ray selecting same objects (at least at lower luminosity), see Hickox et al. 2008.

7. Quasar Luminosity Function As with star formation rate, quasars peaked at redshift 2-3. The rise and fall is even more dramatic in time than redshift. Richards et al. 2006

8. The Rise of Quasars at z~6 Sets an upper limit to the luminosity for a given mass, orequivalentlya minimum mass for a given luminosity. LE = 1.38x1038 M/Msun erg/s ME = 8x107L46Msun Mere existence z~6 quasars constrains formation models Eddington argument: If the luminosity of a quasar is high enough, then radiation pressure from electron scattering will prevent further gravitational infall.

9. Making SMBHs at z~6 The luminosities of the z~6 quasars imply BH masses in excess of 109MSun. But z~6 is <1Gyr after the Big Bang. Assembling that much mass in so little time is difficult (but not impossible). Tanaka & Haiman 2009

10. Quasar Luminosity Function e.g., Richards et al. 2006 SDSS is relatively shallow. It probes only the tip of the iceberg. Need fainter surveys to get full picture.

11. Cosmic Downsizing Hasinger et al. 2005 X-ray surveys probe much deeper. Here we see that peak depends on the luminosity. Ueda et al. 2003

12. Cosmic Downsizing Hasinger et al. 2005 X-ray surveys probe much larger dynamic range. SDSS+2SLAQ Croom et al. 2009

13. How does the quasar luminosity function relate to the physics of BH accretion and galaxy evolution?

14. Quasar Luminosity Function Space density of quasars as a function of redshift and luminosity Typically fit by double power-law Croom et al. 2004

15. Density Evolution Number of quasars is changing as a function of time.

16. Luminosity Evolution Space density of quasars is constant. Brightness of individual (long-lived) quasars is changing.

17. Luminosity vs. Redshift 2.5 1.5 4.5 3.5 0.5 Usually we split into L or z instead of making a 3-D plot, but the information is the same.

18. Luminosity Evolution Cosmic Downsizing • Pure density or pure luminosity evolution don’t lead to cosmic downsizing. • The slopes must evolve with redshift.

19. Luminosity Dependent Density Evolution To get cosmic downsizing, the number of quasar must change as a function of time, as a function of luminosity. i.e., the slopes must evolve.

20. Bolometric QLF Hopkins, Richards, & Hernquist 2007

21. Hopkins et al. 2005 Most QLF models assume they are either “on” or “off” and that there is a mass/luminosity hierarchy. Hopkins et al.: quasar phase is episodic with a much smaller range of mass than previously thought. QLF is the convolution of the formation rate and the lifetime. Hopkins et al. 2006

22. QSO QLF != Galaxy QLF Benson et al. 2003

23. Hopkins et al. 2005 Most QLF models assume they are either “on” or “off” and that there is a mass/luminosity hierarchy. Hopkins et al.: quasar phase is episodic and “all quasars are created equal” (with regard to mass/peak luminosity). QLF is the convolution of the formation rate and the lifetime. Hopkins et al. 2006

24. Merger Scenario w/ Feedback • merge gas-rich galaxies • form buried quasars • feedback expels the gas • revealing the quasar • shutting down accretion and star formation e.g., Kauffmann & Haehnelt 2000 Granato et al. 2004, DiMatteo et al. 2005, Springel et al. 2005, Hopkins et al. 2005/6a-z

25. How Can We Test This? In addition to the evolution of the QLF slopes, we can probe: • The Quasar Luminosity Function • active lifetime (e.g., Martini 2004) • accretion rate (e.g., Kollmeier et al. 2006) • MBH distribution (e.g., Vestergaard & Osmer 2009) • Quasar Clustering • L, zdependence (e.g., Lidz et al. 2006 ; Shen et al. 2009) • small scales (e.g., Hennawi et al. 2006; Myers et al. 2008)

26. Clustering • Red Points are, on average, randomly distributed, black points are clustered • Red points: ()=0 • Black points: ()>0 • Can vary as a function of, e.g., angular distance,  (blue circles) • Red: ()=0 on all scales • Black: () is larger on smaller scales A. Myers

27. Quasar Clustering • Quasars are more clustered on small scales than large scales. • Comparing with models of dark matter clustering gives the “bias” (overdensity of galaxies to DM) • Linear bias (bQ=1) ruled out at high significance. Myers et al. 2007

28. The comoving clustering length of luminous galaxies is roughly independent of z at least to z~ 5. Therefore, the distribution of galaxies must be increasingly biased relative to the dark matter at high redshift, galaxies=bdark matter Galaxy Clustering Ouchi et al. 2004

29. Quasars are powered by the ubiquitous super-massive black holes in the cores of ordinary massive galaxies How about quasars? Therefore, we’d expect that the clustering of quasars should be similar to that of luminous galaxies, at the same redshift. Bahcall, Kirhakos et al.

30. Comoving Correlation Length SDSS Quasars Ross et al. 2009

31. Quasar Bias Evolution As with galaxies, constant clustering length means strongly evolving bias. Ross et al. 2009

32. What happens at higher redshift? • If very massiveBHsare associated with very massive DM halos, then high-redshift quasars should sit in very rare, many  peaks in the density field. • So we expect high-redshift quasars to be more strongly clustered. For 2.9 < z < 3.5: r0=16.9±1.7 Mpc/h; b~10 For z > 3.5: r0=24.3±2.4 b~15 Shen et al. 2007

33. Use ellipsoidal collapse model (Sheth, Mo & Tormen, 2001) to turn estimates of bQinto mass of halos hosting UVX quasars. • Find very little evolution in halo mass with redshift. • Our mean halo mass of ~5x1012h-1MSolar is halfway between characteristic masses from Croom et al. (2005) and Porciani et al. (2004). • This is comparable to the mass of galaxy groups, supporting the idea that quasars are triggered by mergers.

34. Lacey & Cole (1993) Typical quasar hosts double in mass every Gyr or so Constancy of quasar host halo mass thus limits quasar lifetime to around 106.5 to 107.5 yrs Hierarchical Halo Merging CDM theory tells us the expected space density of halos. Comparing with the observed quasar density allows us to determine the fraction of time a quasar is shining. Time for 2x Mass Time Mass

35. Clustering’s Luminosity Dependence Lidz et al. 2006 old model new model • Quasars accreting over a wide range of luminosity are driven by a narrow range of black hole masses • M- relation mean a wide range of quasar luminosities will then occupy a narrow range of MDMH

36. No L Dependence for Quasars galaxies quasars Zehavi et al. 2005 Shen et al. 2007

37. What Next? Measuring bias of faint high-z quasars will break degeneracies between feedback models. faint quasars (e.g., LSST) bright quasars (e.g., SDSS) Richards et al. 2006 Hopkins et al. 2007

38. What We (Used To) Expect Galaxies (and their DM halos) grow through hierarchical mergers Quasars inhabit rarer high-density peaks If quasars long lived, their BHs grow with cosmic time MBH-σ relation implies that the most luminous quasars are in the most massive halos. More luminous quasars should be more strongly clustered (b/c sample higher mass peaks). QLF from wide range of BH masses (DMH masses) and narrow range of accretion rates.

39. What We Get Galaxies (and their DM halos) grow through hierarchical mergers Something causes the growth of galaxies and their BHs to terminate even as DM halos continue to grow Quasars always turn on in potential wells of a certain size (at earlier times these correspond to relatively higher density peaks). Quasars turn off on timescales shorter than hierarchical merger times, are always seen in similar mass halos (on average). MBH-σ relation then implies that quasars trace similar mass black holes (on average) Thus little luminosity dependence to quasar clustering (L depends on accretion rate more than mass). Need a wide range of accretion rates for a narrow range of MBH to be consistent with QLF.