Transcript Probing the Central Regions of Active Galactic Nuclei

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
1
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.
2
Reverberation Mapping
• Kinematics and
geometry of the BLR
can be tightly
constrained by
measuring the emissionline response to
continuum variations.
NGC 5548, the most closely
monitored Seyfert 1 galaxy
Continuum
Emission line
3
Time after continuum outburst
“Isodelay surface”
20 light days
Broad-line region
as a disk,
2–20 light days
Black hole/accretion disk
Time
delay
Line profile at
current time delay
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):
CCF(t ) 
 ( )ACF(t   )d


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.
7
Evidence for a Virialized BLR
• Gravity is important
– Broad-lines show
virial relationship
between size of lineemitting region and
line width, r   2
– Yields measurement
of black-hole mass
 H
 Other Lines
8
Virialized BLR
• The virial relationship
is best seen in the
variable part of the
emission line.
 H
 Other Lines
9
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
Ferrarese slope
Tremaine slope
10
Reverberation Masses:
Separating Fact from Fiction
• Reverberation-based masses are real mass
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?
11
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
Ferrarese slope
Tremaine slope
12
Physical Interpretation of f
• An average over the
projection factors.
• Example: thin ring
M BH
2 c 2

sin 2 i G
~
 f (i ) M
f   f (i ) P (i ) sin i di
Aside: since unification requires 0  i  imax, simple disks
without a polar component are formally ruled out.
13
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)
14
BLR Scaling with Luminosity
• To first order, AGN
spectra look the same:
r  L0.67  0.05
Q( H)
L
U

2
4 r nH c nH r 2
 Same ionization
parameter
 Same density
r  L1/2
Balmer-line region size vs.
optical continuum luminosity
Kaspi et al. (2005)
15
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.
M = f (ccent 2 /G)  L0.5 2
Vestergaard (2002)
16
Estimating AGN Black Hole Masses
Phenomenon:
Primary
Methods:
Fundamental
Empirical
Relationships:
Secondary
Mass
Indicators:
Application:
Quiescent
Galaxies
Stellar, gas
dynamics
Type 2
AGNs
Megamasers
BL Lac
objects
2-d
RM
1-d
RM
AGN MBH – *
MBH – *
Fundamental
plane:
e , r e   *
 MBH
Type 1
AGNs
[O III] line width
V  *  MBH
Low-z AGNs
Broad-line width V
& size scaling with
luminosity
R  L0.5
 MBH
High-z AGNs
Current Goals
1) Reverberation-based masses for AGNs
over a wider luminosity range.
18
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)-LUV Relationship
Kaspi et al. (2005)
slope R(H)  LUV0.56
R(C IV)  LUV0.79
Peterson et al. (2005)
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MBH-* Relationship
Other methods
Reverberation
NGC 4395
21
Current Goals
1) Reverberation-based masses for AGNs
over a wider luminosity range.
2) Clean up the BLR RL relationship.
22
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)
23
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.
24
NGC 3516
NGC 3227
NGC 4151
NGC 4051
NGC 4395
NGC 4593
Preliminary Light Curve for NGC 4593
26
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.
27
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.
28
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)
Program
No. Sources
Time Resolution
Duration
Spectral Resolution
Homogeneity
Signal/Noise Ratio
AGN Watch
AGN Watch AGN Watch AGN Watch
CTIO/
NGC 5548
NGC 4151 NGC 7469
(other)
OSU OSU
IUE 89 HST 93 Opt IUE Opt IUE Opt IUE
Opt Opt Opt
1
1
1
1
1
1
1
3
5
8
2
LAG
Opt
5
Wise Wise/
1988 SO PG
Opt
Opt
3
15
A program to obtain a velocity-delay map is not
much more difficult than what has been done already!
29
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.
30
MBH-* Relationship
Other methods
Reverberation
NGC 4395
31
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.
32
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.
33
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.
34