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Reverberation Mapping of the Broad-Line Region. Bradley M. Peterson The Ohio State University.

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reverberation mapping of the broad line region
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
key points
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.
reverberation mapping
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

slide4

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

emission line lags
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):
reverberation mapping results
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.
evidence for a virialized blr

 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
virialized blr

 H

Other Lines

Virialized BLR
  • The virial relationship is best seen in the variable part of the emission line.
calibration of the reverberation mass scale

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
reverberation masses separating fact from fiction
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?
the virial scaling factor f

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
physical interpretation of f
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.

luminosity effects
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)

blr scaling with luminosity

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)

secondary mass indicators
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

slide17

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:

current goals
Current Goals
  • Reverberation-based masses for AGNs over a wider luminosity range.
ngc 4395 the least luminous and lowest mass seyfert 1 known
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)

r c iv l uv relationship

Kaspi et al. (2005)

slope R(H)  LUV0.56

R(C IV)  LUV0.79

R(C IV)-LUV Relationship

Peterson et al. (2005)

current goals1
Current Goals
  • Reverberation-based masses for AGNs over a wider luminosity range.
  • Clean up the BLR RL relationship.
blr radius luminosity relationship
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)

current goals2
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.
slide25

NGC 3516

NGC 4051

NGC 3227

NGC 4395

NGC 4151

NGC 4593

current goals3
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.
a one step program to better masses
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.

requirements to map the blr
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!

current goals4
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.
current goals5
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.
measuring agn black hole masses from stellar dynamics
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.
summary
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.
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