Presentation on theme: "1 Reverberation Mapping of the Broad-Line Region Bradley M. Peterson The Ohio State University Collaborators: M. Bentz, S. Collin, K. Denney, L.-B. Desroches,"— Presentation transcript:
1 Reverberation Mapping of 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 M BH - * zeropoint –Systematic errors ~0.5 dex Based on scatter in M BH - * relationship –Velocity-delay maps necessary to determine systematic uncertainties.
3 Reverberation Mapping Kinematics and geometry of the BLR can be tightly constrained by measuring the emission- line response to continuum variations. NGC 5548, the most closely monitored Seyfert 1 galaxy Continuum Emission line
Broad-line region as a disk, 2–20 light days Black hole/accretion disk Time after continuum outburst Time delay Line profile at current time delay “Isodelay surface” 20 light days
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 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 H Other Lines
9 Virialized BLR The virial relationship is best seen in the variable part of the emission line. H Other Lines
10 M = f (c cent 2 /G) Determine scale factor f that matches AGNs to the quiescent-galaxy M BH - * relationship Current best estimate: f = 5.5 ± 1.8 Calibration of the Reverberation Mass Scale Tremaine slope Ferrarese slope
11 Reverberation Masses: Separating Fact from Fiction Reverberation-based masses are real mass measurements Reverberation masses are not high-precision masses (yet?) M BH = 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 The Virial Scaling Factor f Scaling factor is empirically determined This removes bias from the ensemble –Equal numbers of masses are overestimated and underestimated M = f (c cent 2 /G) Tremaine slope Ferrarese slope
13 Physical Interpretation of f An average over the projection factors. Example: thin ring Aside: since unification requires 0 i i max, 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 BLR Scaling with Luminosity To first order, AGN spectra look the same: Þ Same ionization parameter Þ Same density r L 1/2 r L 0.67 0.05 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) L 0.5 2
Phenomenon:Quiescent Galaxies Type 2 AGNs Type 1 AGNs Estimating AGN Black Hole Masses Primary Methods: Stellar, gas dynamics Stellar, gas dynamics Megamasers 1-d RM 1-d RM 2-d RM 2-d RM Fundamental Empirical Relationships: M BH – * AGN M BH – * Secondary Mass Indicators: Fundamental plane: e, r e * M BH [O III ] line width V * M BH Broad-line width V & size scaling with luminosity R L 0.5 M BH Application: High-z AGNs Low-z AGNs BL Lac objects
18 Current Goals 1)Reverberation-based masses for AGNs over a wider luminosity range.
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 R(C IV )-L UV Relationship Kaspi et al. (2005) slope R(H ) L UV 0.56 R(C IV ) L UV 0.79 Peterson et al. (2005)
21 M BH - * Relationship Reverberation Other methods NGC 4395
22 Current Goals 1)Reverberation-based masses for AGNs over a wider luminosity range. 2)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 1)Reverberation-based masses for AGNs over a wider luminosity range. 2)Clean up the BLR R L relationship. 3)Re-determine BLR sizes/black-hole masses of bright Seyferts.
NGC 4395 NGC 4051 NGC 3516NGC 3227 NGC 4151 NGC 4593
27 Current Goals 1)Reverberation-based masses for AGNs over a wider luminosity range. 2)Clean up the BLR R L relationship. 3)Re-determine BLR sizes/black-hole masses of bright Seyferts. 4)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 1)Reverberation-based masses for AGNs over a wider luminosity range. 2)Clean up the BLR R L relationship. 3)Re-determine BLR sizes/black-hole masses of bright Seyferts. 4)Velocity-delay map. 5)Improve calibration zero-point for AGN data.
31 M BH - * Relationship Reverberation Other methods NGC 4395
32 Current Goals 1)Reverberation-based masses for AGNs over a wider luminosity range. 2)Clean up the BLR R L relationship. 3)Re-determine BLR sizes/black-hole masses of bright Seyferts. 4)Velocity-delay map. 5)Improve calibration zero-point for AGN data. 6)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.