Transcript Black Hole Demographics

Laura Ferrarese
Rutgers University
Lecture 6: The Future
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SIGRAV Graduate School in Contemporary
Relativity and Gravitational Physics
Lecture Outline
 A Recap of the Observational Status of SBH Research
 Open Questions: What Remains to be Done
1. Building the Local Sample
2. The Redshift Evolution of SBH Scaling Relations
3. The Structure of the Broad Line Region
4. Black Holes and Globular Clusters
5. Binary Supermassive Black Holes.
Estimating SBH Masses
Phenomenon:
BL Lac
Objects
Primary
Methods:
Fundamental
Empirical
Relationships:
Secondary
Mass
Indicators:
Quiescent
Galaxies
Type 2
AGNs
Stellar, gas
dynamics
Megamasers
MBH – *
Fundamental
plane:
e , r e   *
 MBH
Type 1
AGNs
2-d
RM
1-d
RM
AGN MBH – *
[O III] line width
V  *  MBH
Low-z AGNs
Broad-line width V
& size scaling with
luminosity
R  L0.7
 MBH
High-z AGNs
What We Have Learned, and Open
1. SBHs are fundamental constituents ofQuestions
galaxies: the local SBH mass density is equal to what is needed
to explain the energetics of high redshift QSOs (Merritt & Ferrarese 2001; Ferrarese 2002; Yu &
Tremaine 2002).
2. The existence of tight relations between SBHs masses and the large scale properties of their host
galaxies suggests that the formation and evolution of SBHs and their hosts must go hand in hand.
Understanding how SBHs form might help us to understand how galaxies form/evolve (or viceversa).
3. Can we obtain dynamical
evidence for the existence of
IBHs?
An
increasing amount of evidence supports the
Self regulating SBH formation links the mass
of SBHs to that of the dark matter halo in
which they reside. Such models have a built
in lower limit to the SBH mass that can be
created (e.g. Silk & Rees 1998, Haehnelt,
Natarajan & Rees 1998).
existence of “intermediate mass black holes” (100 1000 M), which could be the seeds for nuclear SBHs
(Ebisuzaki et al. 2001; Portegies Zwart & McMillan
2002; Miller & Hamilton 2002)
1. How small or how large can SBHs be?
2. What is the exact characterization
The persistence of the M- relation in the face of
of the SBH-galaxy connections?
mergers probes the cooling/heating feedback of the ISM
(e.g. Kauffmann & Haehnelt 2000).
4. Do binary black holes exist?
The formation of binary black holes as a consequence of mergers can have dramatic consequences,
from driving the morphology and dynamics of the host core (Milosavljevic & Merritt 2001), to destroying
nuclear dark matter halo cusps (Merritt et al. 2002)
Biases and Systematics
Systematics in the M- relation (or any
other SBH scaling relation!) have not
been fully investigated:
 Slope, zero point & scatter
 < 106 M and >109 M  regimes
 Dependence on Hubble type
 Dependence on galaxy
environment
 Cosmic evolution
 Reliability of SBH mass
measurements
SPIRALS
LENTICULARS
ELLIPTICALS
Biases in the Current Mass
Estimates
 In the current sample there is only one galaxy for which a SBH mass estimate has been
obtained using two independent methods (IC1459; Verdoes Kleijn et al. 2000, Cappellari et
al. 2002)


MBH(stars) = (2.6 1.1)  109 M (using 3I modeling of HST/STIS data with N0/Nc=2.0)
MBH(gas) = (0.4 -1.0)  109 M (depending on the assumptions made for the gas
velocity field)
 There is only one galaxy for which the same data has been analyzed by two different teams
using the same method (3-I modeling using different codes - M32, van der Marel et al. 1998,
ApJ, 493, 613; Valluri et al. 2003, astro-ph/0210379):


MBH(vdM) = (3.4 0.7)  106 M
MBH(Valluri) = (1 - 6)  106 M
 Finally, some of the data being analyzed might not be adequate in terms of spatial
resolution and signal-to-noise ration
Resolving the Sphere of Influence
 The quality of the data might very well influence the characterization of the scaling
relations (remember Magorrian et al. 1998…)
Kormendy & Gebhardt 2001,
Gebhardt et al. 2002
Resolving the Sphere of Influence
4.58  0.52
(Ferrarese 2002)
4.02  0.32
(Tremaine et al. 2002)
1. Addressing the Faint End of the M-
Relation
 How far does the M- relation extend?
1. Addressing the Faint End of the M- Relation :
M33
M33 is an ideal target:
HST/STIS/0.1” slit
• very nearby (850 kpc)  tightest limits on a small BH.
• very compact nucleus, reaching a stellar mass density
of several million solar masses per cubic parsec 
ideal conditions for BH formation (?)
• Very low central velocity dispersion (~ 24 km/s,
Kormendy & McClure 1993)  very small black hole
• Inconspicuous bulge  very small black hole (?)
• The M33 nucleus probably contains the most luminous
ULX in the Local Group (Long et al. 1981),
strengthening the connection with the M82 ULXs
(Ebisuzaki et al. 2001)
Tightest limit from ground based data: MBH < 50,000 M
The MBH- relation predicts 2,600 < MBH < 26,000 M
 radius of influence < 0.025 arcsec
 Only an upper limit can be set on the mass.
Merritt, Ferrarese & Joseph (2001)
1. Addressing the Faint End of the M- Relation :
M33
 The upper limit is still consistent with the M- relation.
M33
Gebhardt et al. 2001;
Merritt, Ferrarese & Joseph 2001
1. Addressing the Faint End of the M- Relation :
NGC205
 On-going HST-ACS/NICMOS/STIS project (Ferrarese, Merritt, Valluri, Joseph). Of the
galaxies for expected to harbor a SBH with MBH < 106 M, NGC 205 is the only one for
which the sphere of influence can be resolved by HST in a finite amount of time.
Andromeda, NGC 205 and M32
1.5 X 2 degrees
NGC205 - HST/ACS/HRC - 29X29 arcsec
2. Building the Local Sample: What HST Cannot
Do
 Stellar kinematics in giant ellipticals, all of which have low central surface brightness.
Ferrarese et al. 1994, AJ
 Exposure times requirements with HST/STIS to observe an object like M87 are 4106

seconds (to reach a S/N=50 at 8500 Å).
All giant ellipticals must (and have been) studied using gas kinematics.
2. Building the Local Sample: What HST Cannot
Do
 Nearby dwarf systems
NGC 147 (Han et al. 1997, AJ)
WFPC2, F555W
 Exposure times requirements with HST/STIS to observe an object like NGC147 are 106
seconds (to reach a S/N=50 at 8500 Å)
2. Building the Local Sample
 What if we wanted to, say, increase the current sample size to include significantly
HST
8m
Fornax
Virgo
30m
M101 group

statistical samples of galaxies belonging to all Hubble types and disparate environments?
Below: SBH masses for all galaxies belonging to the CfA redshift sample (Huchra et al.
1990, ApJS, 72, 433), estimated from the bulge luminosity, as a function of distance
2. Building the Local Sample
 The sample thins out even more if S/N requirements are added. The figure shows the
requirements for a complete sample of elliptical galaxies (from Faber 1989) observed with
S/N=50 in the absorption lines at 8500 Å , in the equivalent of 3 HST orbits.
30m 8m HST
2. Building the Local Sample: SBHs
in Low Surface Brightness Galaxies
(?)
 Studies of giant LSB galaxies have
Schombert ‘98
found a ~50% incidence of low
luminosity AGNs (Sprayberry et al.
1995, Schombert 1998).
 This is important for two reasons:
 LSBs are not accounted for in
studies of SBH demographic, but
they could contribute significantly
to the local SBH mass function.
 LSBs differ from HSBs in morphological appearance, past and current SFR, disk
kinematics, mass to light ratios, gas ratios and molecular content. Their SBH mass
function is certain to shed light on the mechanisms of formation and evolution of
SBHs. For instance, could LSBs be be remnants of the most massive QSOs (Silk &
Rees 1999)?
2. Building the Local Sample: SBHs
in Low Surface Brightness Galaxies
(?)

This is a project that could be possibly done with a combination of ground based and HST
observations. For instance:

There are 73 LSB galaxies with z < 5000 km/s in the Impey et al. (1996) catalogue. For
all:
1)
4m-class telescope: low resolution spectra to determine incidence of nuclear
activity. For the AGN subsample:
2)
HST/ACS H images to determine the extent and morphology of the ionized gas
in the nuclear region. For the most promising candidates:
3)
HST/STIS spectra at 0.1 arcsec spatial resolution to determine the nuclear gas
kinematics and constrain the masses of the central SBHs.
3. The Redshift Evolution of the MBH-
Relation
 The most distant objects with a direct SBH mass measurement are at 100 Mpc. However,
studying the MBH- relation as a function of redshift would tell us about the incidence of
merging and accretion on the evolution of SBHs and their host galaxies.
 Even using an 8m diffraction limited telescope, resolved stellar/gas dynamics can probe
109M SBHs only up to a few hundred Mpc away. However, if we restrict ourselves to AGNs,
we do not have to rely on resolved kinematics.
 Is targeting AGNs feasible? Is it a good idea?
 AGN samples are quite large. For instance, in the Veron-Cetty & Veron (2001)
catalogue there are:




13 Seyfert 1s with 1<z<2
3228 northern QSOs with 1.0<z<2.0
1653 northern QSOs with 2.0<z<3.0
In the local Universe, quiescent galaxies and AGNs obey the same scaling relation as
far as the supermassive black holes at the the center are concerned. But is this true
at high redshift? (there is no answer!)
3. The Redshift Evolution of the MBH-
Relation
 “Quick and dirty” approach :
 obtain AGN spectra to 1) estimate the BLR radius from the monochromatic luminosity
at 5100 Å; and 2) the virial velocity from the width of Balmer lines.
From Kaspi et al. (2000)

The SBH mass follows by combining the BLR size (from the continuum luminosity)
with the line width.
 In applying this method to high redshift AGNs, we make two tacit assumptions:
 the RBLR-L5100 relation is valid at high redshifts
 The RBLR-L5100 extends at large luminosities.
3. The Redshift Evolution of the MBH-
Relation
 “Quick and dirty” approach :
 The velocity dispersion can be difficult to estimate at high redshifts. It has been
proposed that the [OIII]5007 FWHM can act as a surrogate for  (Nelson & Whittle
1986, ApJ, 465, 96).
From Nelson & Whittle (1986)
Left: exactly this procedure applied to
a sample of 107 radio quite QSO and
Seyfert 1s (Boroson 2003). Notice the
large scatter.
3. The Redshift Evolution of the MBH-
Relation
 The only attempt at applying this method at high redshift was made by the Shields et al.
(2002). Although the authors conclude that “the MBH- relationship is not a strong
function of redshift… The black hole bulge mass relationship is roughly obeyed at a time
when much of the growth of present day black holes lay in the future”, notice how:
MBH=107 - 3108 M
MBH=109 - 1010 M
From Shields et al. 2002
 only very large SBH masses are probed at high redshift. Therefore the study contains no

information about the slope of the relation, although it does suggest that the relation is
pinned at the very high mass end.
This is to be expected: the largest SBHs must not have changed much since a redshift 3.
3. The Redshift Evolution of the MBH-
Relation
 There is a more direct but much more involved approach to this issue:

Reverberation mapping for selected objects:



needs monitoring at 4d to 3m intervals (depending on luminosity/expected SBH mass) over
periods of 1y to 15y.
Can be carried out with 4m and 8m class telescopes.
Stellar velocity dispersion in the AGN host:



direct measurements have been obtained for QSOs up to z=0.3 using conventional 4m class
telescope (Hughes et al. 2000)
measurements at z=1 can be obtained with an 8m class telescope equipped with AO in the
near IR.
measurements at z=2 are NGST material.
 A project on this scale would likely require international collaboration over at least a
decade, and is not currently being undertaken.
 Furthermore, the reliability of reverberation mapping as a mass estimator ultimately lies in
probing the the structure of BLR. Are we doing anything on this front? (no, but we should
be!)
4. The Structure of the Broad Line
Region
 Based on the experience accumulated so far, accurate mapping of the BLR requires a
number of characteristics:
 High time resolution ( 0.2 day)
 Long duration (several months)
 Moderate spectral resolution ( 600 km s-1)
 High homogeneity and signal-to-noise (~100)
70-cm
UV/optical
telescope
40-cm
X-ray
telescope
KRONOS (PI B. Peterson) is a proposed NASA/Midex
mission which will allow uninterrupted UV/Optical/Xray observations for as long as 14 days on target.
It will allow to distinguish between different simple
transfer functions, something that no experiment to
date has been able to do!
4. The Structure of the BLR:
KRONOS
Ground-based optical image
Hubble Space
Telescope image
Kronos
transfer
function
1023 cm
 100
Kronos
map
1021 cm
 10,000
1017 cm
6. Detecting Binary Black Holes
 Milosavljevic & Merritt 2001 (ApJ) have conducted state of the art N-body simulations
aimed at following the dynamical evolution of a supermassive black hole binary and its
surrounding stellar system following galaxy merging.
0
0.3 - 0.6 Myr
time
0.5-1.1 Myr
Rotational Velocity
Velocity Dispersion
6. Detecting Binary Black Holes
Separation between the SBHs: 0.18 pc (109 M SBHs)
Difference in Rotational Velocity:
95 km/s (109 M SBHs)
Difference in Velocity Dispersion:
136 km/s (109 M SBHs)
From Milosavljevic & Merritt 2001, ApJ
Thick Line: SBH Binary
Thin Line: Single SBH
6. Detecting Binary Black Holes
HST 8m
30m
Summary
Project
Enlarge the
sample; probe <
106 & > 109 M
SBHs; test
biases with
type &
environment
Detecting SBHs
in GCs
Spatial Resol. Aperture
< 0.02 arcsec > 8m few tens of arcsec
l/Dl
Comments
5500-9500
10,000
Longslit
IFU
Constrain dynamical models for GC evolution; investigate the connection
between GCs, nuclear SBHs and galactic bulge. Same data useful to measure GC
distances, constrain ages.
HST
few tens of arcsec
U or B-band N/A
High Res. Imaging
High Dynamic Range
Constrain dynamical models for galaxy mergers; determine the impact of SBH
binaries in the morphological evolution of galaxies; constrain accretion
mechanisms.
<0.01 arcsec
Constrain the
redshift
evolution of
SBH scaling
relations
Bandpass
Needed to study systematics, distinguish between “bottom up” or “top down”
models for SBH formation; constrain the role of feedback in SBH accretion during
merging.
~ 0.1 arcsec
Resolving
Binary SBHs
FOV
>30m few tens of arcsec
>8000
Constrain SBHs formation and evolution.
Reverberation mapping, KRONOS.
10,000
IFU
Suggested Readings
 Thoughts about future work:
Ferrarese, L. 2002, in ‘Hubble's Science Legacy:
Future Optical-Ultraviolet Astronomy from Space’, `
astroph/0207050
Peterson 2002, in ‘Hubble's Science Legacy: Future
Optical-Ultraviolet Astronomy from Space’,
astroph/0208066