SIGRAV Graduate School in Contemporary

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Laura Ferrarese Rutgers University lff_at_physics.rut
gers.edu Observational Evidence For Supermassive
Black Holes. Lecture 1 Motivation

• SIGRAV Graduate School in Contemporary
• Relativity and Gravitational Physics

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Lectures Outline

• Lecture 1 Introduction and Motivation
• Lecture 2 Stellar Dynamics
• Lecture 3 Gas Dynamics
• Lecture 4 AGNs and Reverberation Mapping
• Lecture 5 Scaling Relations
• Lecture 6 What the Future Might Bring
• ALL LECTURES ARE ON-LINE
• http//www.physics.rutgers.edu/lff/Como
• Username como
• Password sigrav
• http//dipastro.pd.astro.it/bertola/astrofisica.ht
  ml

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Lecture 1 Outline

• Motivation Why Do We Think Supermassive Black
  Holes Exist, and Where Should We Look if We
  Wanted to Find One?
• The Mass Density in the Supermassive Black Holes
  Powering Quasar Activity
• The Mass Density in the Supermassive Black Holes
  Powering Local AGNs
• Supermassive Black Hole Detections

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Historical Overview

• Although unrealized at the time, the first hint
  of the existence of supermassive black holes was
  unveiled with
• Karl Janskys 1932 discovery of radio emission
  from the Galactic center.
• Carl Seyferts 1943 discovery of the peculiar
  spiral galaxies which today carry his name.
• By the 1960, several hundred radio sources had
  been
• discovered, and astronomers were struggling to
  find
• optical counterparts.
• In 1960, Allan Sandage identified 3C48 with a
  single blue
• point of light. In the two years after Sandages
  discovery of
• the optical counterpart to 3C48, a half dozen
  such objects
• were discovered to distinguish them from radio
  galaxies,
• for which the optical emission is clearly
  resolved, objects
• like 3C48 were named quasi stellar radio objects
  or quasars.

Karl Jansky
3C 48
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Historical Overview
Ground based optical images of 3C273
Optical jet
Hubble Space Telescope images of 3C273, revealing
the underlying galaxy
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Quasars

• The spectral energy distribution of quasars (and
  AGNs in general) is markedly non-stellar.

SED for 3C273 green contribution from the
outer jet blue contribution from the host
galaxy. http//obswww.unige.ch/3c273/
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Quasars

• The night after observing the optical counterpart
  to 3C48, Sandage took a spectrum, which he
  described as the weirdest spectrum I had ever
  seen. The spectrum had several emission lines,
  but none seemed to correspond to known elements.
• The impasse was broken by Maarten Schmidt in
  1963.
• Schmidt realized that the emission lines in the
  spectrum
• of 3C273, were the very familiar hydrogen Balmer
  lines,
• but redshifted by v/c 0.158. It was soon
  realized that
• all quasar spectra could be interpreted this
  way.
• Although controversial for a long time, it is now
  recognized
• that quasar redshifts are cosmological.

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Quasars

• 3C273, and all quasars, show flux variability on
  timescales of hours to months (depending on the
  frequency)

3C273 http//obswww.unige.ch/3c273/
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Quasars

• ENERGY OUTPUT At cosmological distances, quasars
  must be hundreds to many tens of thousand times
  more luminous than an L galaxy.
• In general, AGNs bolometric luminosity are of
  order 1044-1048 erg s-1
• In the Eddington approximation, this implies
  masses LE 4? GMBH mp/?T and assuming a typical
  quasar lifetime of order 107 yr ? MBH gt 106 M?
• SIZE The time variability sets very tight limits
  on the size of the emitting region, which must be
  smaller than the distance light can travel in
  that time
• Even if the brightness changes at every point
  simultaneously, the change happening at point A
  would reach us sooner than the change from point
  B. It will take the time for light to travel from
  point B to point A for an observer to perceive
  the full change.
• This implies that the emitting region is less
  than a few light weeks or days across.
• Combined with the constraints on the mass, the
  implied central densities are of order 1015 M?pc-3

Brightness
Time
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Quasars

• COHERENCE jet stability and collimation over
  hundred of kiloparsecs in some objects imply a
  stable energy source.

1Mpc
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AGNs

• RELATIVISTIC MOTIONS one of the greatest
  surprises provided by very-long baseline
  interferometry (VLBI) observations was the fact
  that some AGNs exhibit motion along their jets
  with speeds which appear to be several times
  faster than light.

5000 light years
Sequence of HST images showing blobs in the M87
jet apparently moving at six times the speed of
light. The slanting lines track the moving
features.
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• Energetics, sizes, densities, coherence, and the
  presence of relativistic motions imply that the
  power supply is gravitational central engines
  are relativistic, massive, compact and good
  gyroscopes.
• A massive black hole is the inevitable end result
  of nuclear runaway

From Rees 1984, ARAA 22, 471
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The Relativistic Region

• Evidence for a Strong Field Regime 6.4 keV Fe K?
  emission is the most compelling case of the
  existence of an accretion disk at 3-10Rs from a
  central BH (Fabian et al. 1989, 1995 Nandra et
  al. 1997, Iwasawa et al. 1999). Line widths reach
  105 km s-1
• Potential way to constrain
• spin of the BH
• accretion rate
• central mass
• (Fabian et al. 1989, Martocchia et al. 2000)

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Where to Look Punchline

• Quasars were much more common in the past the
  quasar era occurred when the Universe was only
  10-20 of its present age.
• Simple arguments indicate that the cumulative
  mass density in supermassive black holes powering
  quasar activity is of order
• ?BH(QSO) 3 - 4 ?105 M? Mpc-3
• However, the mass density in supermassive black
  holes at the centers of local AGNs is a full two
  order of magnitudes lower!
• Where have the quasars gone?
• The bulk of the mass connected with the accretion
  in high redshift QSOs does not reside in local
  AGNs.
• ? Remnants of past activity must be present in a
  large number of quiescent galaxies.

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Where to Look

• Our journey into SBH demographics stars from
  quasars lets try to follow their evolution from
  the study of the luminosity function (number of
  quasars per unit comoving volume).
• LOW REDSHIFTS (z lt 2.3) (Boyle et al. 2000,
  MNRAS, 317, 1014)
• The 2-degree field QSO Redshift survey includes
  redshifts for gt 25000 18.25ltBlt20.85 QSOs in two
  75 5 declination strips in the South Galactic
  Pole and in an equatorial region at the North
  Galactic cap. Data were collected using the AAT
  Two-Degree Field (2dF) multi-object
  spectrographic system, which allows up to 400
  spectra to be obtained at once.
• http//www.aao.gov.au/2df/
• http//www.2dfquasar.org/
• HIGH REDSHIFTS (z gt 3.5) (Fan et al. 2001, AJ,
  121, 54)
• The Sloan Digital Sky Survey First Data Release
  includes photometric data based on five-band
  imaging observations of 2099 square degrees of
  sky. Based on these photometric data, spectra
  were obtained for 150,000 galaxies and quasars.
  The survey will ultimately cover 1/4 of the sky,
  and is currently 65 complete for imaging, and
  44 complete for spectroscopy.
• http//www.sdss.org/

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The 2dF Quasar Survey
Completeness
QSO distribution
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The 2dF Quasar Survey

• The quasar optical luminosity function (LF) for
  ten separate data subsets divided by redshift.
  Over the redshift range 0.35 lt z lt 2.3 the LF is
  approximated by a pure luminosity evolution, i.e.
  the form of the LF does not vary with redshift,
  but is simply shifted to higher luminosity. Note
  that the shape and evolution at low redshifts (z
  lt 0.5) and high luminosities are not currently
  well sampled by the survey.

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THe SDSS Quasar Survey

• The LF is derived from 39 luminous QSOs over the
  range 3.6ltzlt5.0, and -27.5ltM1450lt-25.5. The
  luminous quasar density decreases by a factor of
  6 from z 3.5 to z 5.0. The luminosity
  function at the bright end is significantly
  flatter than the bright end luminosity function
  found at zlt3, suggesting that the quasar
  evolution from z2 to z5 cannot be described as
  pure luminosity evolution (Fan et al. 2001, AJ,
  121, 54).
• The survey has also detected 4 quasars at
  redshift gt 6, including the current record holder
  at z6.48 (Fan et al. astro-ph/0301135)

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SBHs in High Redshift Quasars
Fan et al. 2001, Boyle et al. 2000

• QSO Mass Function (0.3 lt z lt 5)
• (Soltan 1982, MNRAS, 200, 115 Chokshi Turner
  1992, Small Blandford 1992, Salucci et al.
  1998)
• 1) Luminosity Function
• 2) Integrated comoving energy density
• 3) Integrated comoving mass density

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SBHs in High Redshift Quasars
Ferrarese 2002 (astroph/0203047)

• A note of caution
• The magnitude limits of the 2dF and SDSS samples
  correspond to Eddington limits on the masses of
  4.5?107 M? and 7.3?108 M? respectively.
• The quasar LF has no coverage in the 2.3 lt z lt
  3.0 redshift range.
• See also Yu Tremaine 2002 (MNRAS 335, 965)

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SBHs in High Redshift Quasars

• Accounting for the diffuse X-ray background
  requires most quasars to be hidden behind large
  amounts of dust and gas, significantly increasing
  the total quasar luminosity of the Universe
  (Maiolino Rieke 1995 Fabian Iwasawa 1999
  Mushotzky et al. 2000 Barger et al. 2001 Gilli,
  Salviati Hasinger 2001 Elvis, Risaliti
  Zamorani 2002 Hasinger 2002 Ghandi Fabian
  2002)
• Fabian Iwasawa (1999)
• Elvis, Risaliti Zamorani (2002)
• Barger et al. (2001)
• Gilli, Salviati Hasinger (2002)
• Ghandi Fabian (2002)

Gilli, Salviati Hasinger 2002
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SBHs in Local AGNs

• Local AGN Mass Function (0 lt z lt 0.2)
• (Padovani et al. 1990, ApJ, 353, 438)
• Need a way to estimate MBH in a complete sample
  of galaxies
• Assume that the BLR clouds are gravitationally
  bound
• MBHv2r/G
• with r size of the Broad Line Region measured
  from
• ? Reverberation mapping (Blandford McKee,
  Peterson 2001)
• Photoionization methods (Padovani et al.
• 1990 Wandel Peterson Malkan 1998)

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How to Do It

• How can we constrain the masses of supermassive
  black holes?
• naively, we might think that the presence of a
  SBH will create a cusp in the brightness profile
  of the host galaxy.
• It does, but..

From Kormendy Richstone 1995, ARAA, 33, 581
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How to Do It
Primary Methods
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Detections of SBHs in the Local Universe
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Detecting Supermassive Black Holes in Local
Galaxies

• With the exception of the Iron K? observations,
  every other technique used to measure
  supermassive black holes masses probes regions
  well beyond the strong field regime.

In units of the Schwarzschild radius RS GM/c2
1.5 ? 1013 M8 cm .
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Preview Scaling Relations
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Suggested Readings

• Iron Kapha Line Reynolds Nowak 2003,
  astro-ph/0212065
• SBH Demographics Soltan 1982, MNRAS, 200, 115
• Ferrarese 2002, in Current high-energy
  emission around black holes, Eds by C.-H. Lee
  and H.-Y. Chang. Singapore World Scientific
  Publishing, p.3, astro-ph/0203047
• Yu Tremaine 2002, MNRAS, 335, 965
• Quasar Luminosity Function Fan et al. 2001, AJ,
  121, 54
• Boyle et al. 2000, MNRAS, 317, 1014