SIGRAV Graduate School in Contemporary SIGRAV Graduate School in Contemporary

Relativity and Gravitational PhysicsRelativity and Gravitational Physics

Laura FerrareseLaura FerrareseRutgers UniversityRutgers University

lff@physics.rutgers.edulff@physics.rutgers.edu

Observational Evidence Observational Evidence For Supermassive Black For Supermassive Black

Holes.Holes.Lecture 1: MotivationLecture 1: Motivation

Lectures OutlineLectures 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: comoPassword: sigrav

&http://dipastro.pd.astro.it/bertola/astrofisica.html

Lecture 1: OutlineLecture 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

Historical OverviewHistorical Overview Although unrealized at the time, the first hint of the existence of

supermassive black holes was unveiled with: Karl Jansky’s 1932 discovery of radio emission from the Galactic center. Carl Seyfert’s 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 Sandage’s 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

Historical OverviewHistorical OverviewGround based optical images of 3C273

Optical jet

Hubble Space Telescope images of 3C273, revealing the underlying galaxy

QuasarsQuasars The spectral energy

distribution of quasars (and AGNs in general) is markedly non-stellar.

SED for 3C273: green: contribution from the outer jetblue: contribution from the host galaxy. http://obswww.unige.ch/3c273/

QuasarsQuasars 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 recognizedthat quasar redshifts are cosmological.

QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.

Optical Spectrum of 3C273

Maarten Schmidt

QuasarsQuasars 3C273, and all quasars, show flux variability on timescales of hours to

months (depending on the frequency)3C273: http://obswww.unige.ch/3c273/

QuasarsQuasars 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 10441048 erg s1

In the Eddington approximation, this implies masses LE = 4 GMBH mp/T; and assuming a typical quasar lifetime of order 107 yr MBH > 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 Mpc-3

A B TimeBri

gh

tnessA B

A BA B

QuasarsQuasars COHERENCE: jet stability and collimation over hundred of kiloparsecs in

some objects imply a stable energy source.

QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.

~ 1Mpc

AGNsAGNs 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.

From Rees 1984, ARA&A 22, 471

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

Composite Spectrum of 18 AGNs observed with ASCA (Nandra et al. 1997)

0.3 c

The Relativistic RegionThe Relativistic RegionEvidence 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: 1)spin of the BH; 2)accretion rate; 3)central mass

(Fabian et al. 1989, Martocchia et al. 2000)

Where to Look: PunchlineWhere 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.

Where to LookWhere to Look Our journey into SBH demographics stars from quasars: let’s try to follow

their evolution from the study of the luminosity function (number of quasars per unit comoving volume).

LOW REDSHIFTS (z < 2.3) (Boyle et al. 2000, MNRAS, 317, 1014):

The 2-degree field QSO Redshift survey includes redshifts for > 25000 18.25<B<20.85 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 > 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/

The 2dF Quasar SurveyThe 2dF Quasar Survey

QSO distribution

Completeness

THe SDSS Quasar SurveyTHe SDSS Quasar Survey The LF is derived from 39 luminous QSOs over the range 3.6<z<5.0, and -

27.5<M1450<-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 z<3, suggesting that the quasar evolution from z=2 to z=5 cannot be described as pure luminosity evolution (Fan et al. 2001, AJ, 121, 54).

The survey has also detected 4 quasars at redshift > 6, including the current record holder at z=6.48 (Fan et al. astro-ph/0301135)

Fan et al. 2001, Boyle et al. 2000

€

QSO (> M) =Kbol

ε c2

L'Ψ(L',z)

H0(1+ z) Ωm (1+ z)3 + ΩΛL

∞

∫0

∞

∫ dL'dz

ρBH =10ρrad

ε0.1c2

SBHs in High Redshift QuasarsSBHs in High Redshift QuasarsQSO Mass Function (0.3 < z < 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

€

Ψ(L,z) = ρ(z)φ(L /L(z))

ρradiation= LΨ(L,z)dLdτdz0

∞

∫0

∞

∫ dz

SBHs in High Redshift QuasarsSBHs in High Redshift Quasars

A note of caution:

The magnitude limits of the 2dF and SDSS samples correspond to Eddington limits on the masses of 4.5107 M and 7.3108 M

respectively.

The quasar LF has no coverage in the 2.3 < z < 3.0 redshift range.

See also Yu & Tremaine 2002 (MNRAS 335, 965)

Ferrarese 2002 (astroph/0203047)

The bulk of the mass connected with the accretion of high z QSOs does not reside in local AGNs. Remnants of past activity must be present in a large number of

quiescent galaxies

Local AGN Mass Function (0 < z < 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:

MBH=v2r/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)

SBHs in Local AGNsSBHs in Local AGNs

How to Do ItHow 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

Stellar or gas

dynamics

NGC205 - HST/ACS/HRC - 29X29 arcsec

NGC4261 - HST/WFPC2

Water Megamasers

NGC4258 (Seyfert 2)

ReverberationMapping

PrimaryMethods:

Phenomenon: QuiescentGalaxies

Type 2AGNs

Type 1AGNs

How to Do ItHow to Do It

Detections of SBHs in the Local Universe

Detections of SBHs in the Local Universe

MethodSBH Mass

(M)Innermost

radius probed

Implied density (M pc-3)

Reverberation MappingThree dozen Seyfert 1s and quasars

5 106

to

5 108

a few light days

~1012

Stellar Kinematics (proper motion):Milky Way

3.7 106

0.008 pc 1 1017

Water Masers:Type 2 AGNs (NGC 4258 & Circunus)

4 107 0.13 pc 1 1012

Kinematics of gas disks:9 galaxies, mainly large ellipticals with low luminosity AGNs

Stellar kinematics:10 galaxies, mainly smaller, rotational supported ellipticals

4 107

to

4 109

>0.4 pc, buttypically>3.

5pc

< 1 107, typically

104

Detecting Supermassive Black Holes in Local Galaxies

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.

Source Distance fromcentral source

X-Ray Fe K 3-10 RS

Broad-Line Region 600 RS

Prope r Motio n (MW) 2000 RS

Megamasers 4 ×104 RS

Ga s Dynamics 8 ×105 RS

Stella r Dynamics 106 RS

In units of the Schwarzschild radius RS = GM/c2 = 1.5 1013 M8 cm .

Preview: Scaling RelationsPreview: Scaling Relations

Suggested ReadingsSuggested 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