Reverberation Mapping of the Broad-Line Region

1. Reverberation Mappingof the Broad-Line Region Bradley M. Peterson The Ohio State University • Collaborators:M. Bentz, S. Collin, K. Denney, L.-B. Desroches, L. Ferrarese, A.V. Filippenko, K.M. Gilbert, L. Ho, K. Horne, S. Kaspi, T. Kawaguchi, C. Kuehn, A. Laor, M.A. Malkan, D. Maoz, D. Merritt, K. Metzroth, E. Moran, H. Netzer, • C.A. Onken, R.W. Pogge, A.C. Quillen, • S.G. Sergeev, M. Vestergaard, A. Wandel

2. Key Points • Despite the likely complexity of the BLR, simple measurements of its size and velocity dispersion yield black hole masses • Random errors ~30% • From measurement errors in lags and line widths • Calibration error ~35% • Uncertainty in calibration of AGN MBH-* zeropoint • Systematic errors ~0.5 dex • Based on scatter in MBH-* relationship • Velocity-delay maps necessary to determine systematic uncertainties.

3. Reverberation Mapping Continuum • Kinematics and geometry of the BLR can be tightly constrained by measuring the emission-line response to continuum variations. Emission line NGC 5548, the most closely monitored Seyfert 1 galaxy

4. Time after continuum outburst “Isodelay surface” Time delay 20 light days Broad-line region as a disk, 2–20 light days Line profile at current time delay Black hole/accretion disk

6. Emission-Line Lags • Because the data requirements are relatively modest, • rather than attempt to obtain the velocity-delay map, • it is most common to determine the cross-correlation • function and obtain the “lag” (mean response time):

7. Reverberation Mapping Results • Reverberation lags have been measured for 36 AGNs, mostly for H, but in some cases for multiple lines. • AGNs with lags for multiple lines show that highest ionization emission lines respond most rapidly  ionization stratification.

8.  H Other Lines Evidence for a Virialized BLR • Gravity is important • Broad-lines show virial relationship between size of line-emitting region and line width, r 2 • Yields measurement of black-hole mass

9.  H Other Lines Virialized BLR • The virial relationship is best seen in the variable part of the emission line.

10. Ferrarese slope Tremaine slope Calibration of the Reverberation Mass Scale M = f (ccent 2 /G) • Determine scale factor f that matches AGNs to the quiescent-galaxy MBH-*relationship • Current best estimate: f = 5.5 ± 1.8

11. Reverberation Masses: Separating Fact from Fiction • Reverberation-based masses are realmass measurements • Reverberation masses are not high-precision masses (yet?) MBH = f c2/G • ~30% uncertainty in precision • How well are lags and line widths measured? • ~35% uncertainty in zero-point calibration • How well is scaling factor f determined? • ~0.5 dex (factor of 3) uncertainty in accuracy for any given AGN • How accurate is the inferred mass?

12. Ferrarese slope Tremaine slope The Virial Scaling Factor f M = f (ccent 2 /G) • Scaling factor is empirically determined • This removes bias from the ensemble • Equal numbers of masses are overestimated and underestimated

13. Physical Interpretation of f • An average over the projection factors. • Example: thin ring Aside: since unification requires 0  i  imax, simple disks without a polar component are formally ruled out.

14. Luminosity Effects • Average line spectra of AGNs are amazingly similar over a wide range of luminosity. • Exception: Baldwin Effect • Relative to continuum, C IV1549 is weaker in more luminous objects • Origin unknown SDSS composites, by luminosity Vanden Berk et al. (2004)

15. r L1/2 BLR Scaling with Luminosity • To first order, AGN spectra look the same: r L0.67  0.05 • Same ionization parameter • Same density Balmer-line region size vs. optical continuum luminosity Kaspi et al. (2005)

16. Secondary Mass Indicators • Reverberation masses serve as an anchor for related AGN mass determinations. • Allows exploration of AGN black hole demographics over the history of the Universe. Vestergaard (2002) M = f (ccent 2 /G)  L0.5 2

17. Type 2 AGNs Type 1 AGNs Phenomenon: Quiescent Galaxies 2-d RM Primary Methods: Stellar, gas dynamics Stellar, gas dynamics Megamasers Megamasers 2-d RM 1-d RM 1-d RM Fundamental Empirical Relationships: MBH– * AGNMBH– * Secondary Mass Indicators: Fundamental plane: e, re  * MBH [O III] line width V  * MBH Broad-line width V & size scaling with luminosity R  L0.5 MBH BL Lac objects Low-z AGNs High-z AGNs Estimating AGN Black Hole Masses Application:

18. Current Goals • Reverberation-based masses for AGNs over a wider luminosity range.

19. NGC 4395: The Least Luminous and Lowest Mass Seyfert 1 Known • Reverberation experiment was carried out with HST STIS in two 5-orbit visits in 2004 April and July. NGC 4395, a bulgeless (Sd) galaxy (Filippenko & Sargent 1989)

20. Kaspi et al. (2005) slope R(H)  LUV0.56 R(C IV)  LUV0.79 R(C IV)-LUV Relationship Peterson et al. (2005)

21. Other methods Reverberation MBH-*Relationship NGC 4395

22. Current Goals • Reverberation-based masses for AGNs over a wider luminosity range. • Clean up the BLR RL relationship.

23. BLR Radius-Luminosity Relationship • Host galaxy light is a major contributor to the luminosity at the faint end. • This tends to make the R-L relationship steeper than it should be. Bentz et al. (2005)

24. Current Goals • Reverberation-based masses for AGNs over a wider luminosity range. • Clean up the BLR RL relationship. • Re-determine BLR sizes/black-hole masses of bright Seyferts.

25. NGC 3516 NGC 4051 NGC 3227 NGC 4395 NGC 4151 NGC 4593

26. Preliminary Light Curve for NGC 4593

27. Current Goals • Reverberation-based masses for AGNs over a wider luminosity range. • Clean up the BLR RL relationship. • Re-determine BLR sizes/black-hole masses of bright Seyferts. • Velocity-delay map.

28. A One-Step Program to Better Masses • Obtain a high-fidelity velocity-delay map for at least one line in one AGN. • Cannot assess systematic uncertainties without knowing geometry/kinematics of BLR. • Even one success would constitute “proof of concept”. BLR with a spiral wave and its velocity-delay map in three emission lines.

29. Requirements to Map the BLR • Extensive simulations based on realistic behavior. • Accurate mapping requires a number of characteristics (nominal values follow for typical Seyfert 1 galaxies): • High time resolution ( 1 day) • Long duration (several months) • Moderate spectral resolution ( 600 km s-1) • High homogeneity and signal-to-noise (~100) A program to obtain a velocity-delay map is not much more difficult than what has been done already!

30. Current Goals • Reverberation-based masses for AGNs over a wider luminosity range. • Clean up the BLR RL relationship. • Re-determine BLR sizes/black-hole masses of bright Seyferts. • Velocity-delay map. • Improve calibration zero-point for AGN data.

31. Other methods Reverberation MBH-*Relationship NGC 4395

32. Current Goals • Reverberation-based masses for AGNs over a wider luminosity range. • Clean up the BLR RL relationship. • Re-determine BLR sizes/black-hole masses of bright Seyferts. • Velocity-delay map. • Improve calibration zero-point for AGN data. • Direct comparison of reverberation mass with mass from another method.

33. Measuring AGN Black Hole Masses from Stellar Dynamics • Only a few AGNs are close enough to resolve their black hole radius of influence with diffraction-limited telescopes. • HST STIS long-slit experiment on NGC 4151 failed because dynamics are too complicated.

34. Summary • Good progress has been made in using reverberation mapping to measure BLR radii and corresponding black hole masses. • 36 AGNs, some in multiple emission lines. • Reverberation-based masses appear to be accurate to a factor of about 3. • Masses from R-L scaling relationship are accurate to about a factor of 4. • Full potential of reverberation mapping has not yet been realized. • Significant improvements in quality of results are within reach.