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The Structure and Energetics of Active Galactic Nuclei
Bradley M. Peterson The Ohio State University

2002 April 4

Hubble Science Legacy

1

The AGN Paradigm
· The black-hole + accretion-disk model is finally fairly secure
Black-hole mass measurements have unknown systematic uncertainties

· No generally accepted models for emission and absorption regions, though disk-related outflows seem most promising
2002 April 4 Hubble Science Legacy 2

Major AGN Questions
· What are the masses AGN black holes? · What are the energetics of the accretion process? & L = h M c2

Accretion rate Mass accretion rate Radiative efficiency efficiency Kinetic energy (jets, absorbing gas)

· How does the AGN mass function evolve over time? · What is the nature of the line emitting and absorbing gas in AGNs ?
2002 April 4 Hubble Science Legacy 3

AGN Black Hole Masses
· Measured for nearly 40 AGNs via reverberation mapping · Secondary methods are tied to these · Evidence these are meaningful estimates:
Virial relationship between line widths and time delays
Onken and Peterson 2002 Peterson and Wandel 2000
2002 April 4 Hubble Science Legacy 4

AGN Black Hole Masses
· Evidence these are meaningful estimates:
MBH - relationship same in AGNs and quiescent galaxies

· What we need:
Direct comparison of reverberation and stellar dynamical masses Two-dimensional reverberation-mapping to understand kinematics and geometry of line-emitting region
Ferrarese et al. 2001
2002 April 4 Hubble Science Legacy 5

Direct Comparison of Reverberation and Stellar Dynamical Masses
· Requires spatially resolving the blackhole radius of influence r* = GMBH/ 2.

Impose criterion on diffraction limit and use MBH - relationship ( MBH 2/9):
f
diff

<

r*

D

M

BH

s

2

D

M

5/9 BH

D

This gives minimum dynamically measurable MBH as a function of distance.
2002 April 4 Hubble Science Legacy 6

2002 April 4

Hubble Science Legacy

7

Why Must This Be Done From Space?
· A ground-based large telescope should be able to attain comparable resolution with adaptive optics (AO) · However, AO Strehl ratios are still too small: the faint stellar absorption features are swamped by scattered nuclear light
2002 April 4 Hubble Science Legacy 8

X-ray/UV Absorption
· Ubiquitous property of AGNs · Large column densities, multiple velocity components, massive outflows · Analogs to outflows in young stars? · Connection to BALs in luminous QSOs? · How much mass and kinetic energy is involved? · How do these vary with AGN properties?
Hubble Science Legacy 9

Chandra

Chandra: Kaspi et al. 2002 HST: Crenshaw et al. 2002 FUSE: Gabel et al. 2002
2002 April 4

Why Is A Large Space Telescope Needed?
· Resolution needs to reach thermal width (~10 km s-1, or R = 30,000) to resolve velocity components · Large collecting area since these are faint sources · Must be done in the UV (resonance lines), must be done at low redshift (complex absorption structures in lower luminosity objects)
2002 April 4

· Variability and weak fine structure lines probe physical conditions in absorbing gas
10

Hubble Science Legacy

Extended Structures
· AGNs show small-scale structures at the highest spatial resolution · 8-m diffraction limit yields spatial resolution on scales of several parsecs, where outflow and fueling structures might become apparent · Evolution of AGN host galaxies out to z 1 can also be probed in rest-frame optical
2002 April 4

3 kpc

NGC 3393 WFPC2 F606W Spatial resolution ~30 pc
11

Hubble Science Legacy

Formation and Evolution of Galaxies
· Bulges and supermassive black holes are intimately related · A small percentage of current SMBHs are active, but these are important as tracers and as examples of how the accretion process works · We need to understand the energetics of the process, both the radiative and kinetic output, to understand galaxy evolution · Understanding galaxy evolution requires understanding black-hole evolution
2002 April 4 Hubble Science Legacy 12

Comment on Space Astronomy Infrastructure
· To make efficient use of very large telescopes, we must off-load essential work that can be done with smaller telescopes
A generally recognized principle in ground-based astronomy UV data are too critical to do without We need smaller workhorse facilities as part of the space astronomy infrastructure A 1-m class UV spectroscopic telescope fits into a MIDEX funding envelope(~$200M) and ELV (e.g., Delta II with 10-ft fairing)
2002 April 4 Hubble Science Legacy 13