Today's News

• Yesterday In Nature the object with thehighest ratio of BH mass to total galaxymass 2:3 was discovered.

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• But NGC 1277is stranger still,and could helpadvance ourtheories ofhow blackholes evolve inthe first place.

• "This galaxyseems to bevery old," DrVan den Boschsaid. "Sosomehow thisblack holegrew veryquickly a longtime ago, butsince then thatgalaxy hasbeen sittingthere notforming anynew stars oranything else.

Optical Propertiesof AGN

• Strong lines ofhydrogen, carbon,silicon ….

Unusual optical colors(Richards et al SDSS)- quasarsin color, stars are black

UV-Optical Continuum isthought to arise via thermalemission in an accretion disk

Cut off due to abs by Heither in host galaxy or IGM

Broad BandProperties of AGN

• Broad bandcontinuum- verydifferent from starsor galaxies

• Strong UV lines notseen in stars ….

• Can be very variable

γ-rayX-ray

Optical-UV

Radio

Ener

gy p

er u

nit f

requ

ency

Log frequency

Range of 104

Broad band spectralenergy distribution (SED)of a 'blazar' (an activegalaxy whose observedradiation is dominated bya relativistic jet 'coming at'usA large fraction of thetotal energy appears in theγ-ray band

Optical Emission Lines

• Remember that starforming galaxiesalso can havestrong emissionlines

• AGN emission lineratios are different-indicatingionization by adifferent type ofsource ('harder'spectrum- moreenergy at shorterwavlengths thanstars)

line ratio plot NII/Hαcompared to OIII/Hβ− AGN lie in aparticlar part of this diagramDarkness of plot is log of thenumber of objects inside thecontour

Broad Band Continuum (IR-Xray)

Nucleus 'invisible' in UV/optical

x-ray IR

Nucleus very bright in UV/optical

X-rays reduced by absorption by cold gas

12/2/12 8

Active Galactic Nuclei

• M87 is example of a radioloud “active galacticnucleus”

• Material flows (accretes)into black hole

• Energy released byaccretion of matter powersenergetic phenomena

• The Jet– Jet of material squirted from

vicinity of SMBH– Lorentz factor of >6– Can be very energetic (particle

luminosity)– in radio to x-ray band jet

radiation is primarilysynchrotron (see text)- ingamma-ray it is inverseCompton

• What powers the jet?– Accretion power– Extraction of spin-energy of

the black hole

AGN 'Types' The Radio-loud/Radio-quiet dichotomy

VLA image of the radio galaxyCygnus-A

Radio jets are very multiscale!

The Radio-loud/Radio-quietdichotomy

Accretion rate (Eddington Units)

Rad

io lo

udne

ss (

L rad

/LB)

Sikora et al. (2007)

Define relative importance of radio emission by ratio ofradio luminosity Lrad to optical luminosity LB- 8 order of magnituderange

X-ray Selection of Activegalaxies

• X-ray andoptical imageof a nearbyAGNNGC4051-

• Note the veryhigh contrastin the x-rayimage

• Find x-rayAGN via– luminous*

pointlike x-ray source innucleus ofgalaxy

– hard x-rayspectrum

– frequentlyvariable

* Find lots ofAGN 'hidden'at otherwavelengths

Rosat x-ray all skysurveyimageoverlaidon skysurveyimage

Rapid variability in AGNSource luminosity ~5x1043 ergs/sec

MCG-6-30-15

Simple argument: source size R~cδt

Broad Range of Properties

Luminosity Range from <1040 erg/s to ~1048 erg/s Fundamental parameters controlling L are

mass and mass accretion rate Most Powerful objects ( quasars )- AGN

totally outshines host galaxy Level of obscuration- how much material is in

our line of sight In some objects, can see all of the way

down to the SMBH (type I) In other objects, view at some wavelengths

is blocked by obscuring material (someobjects are blocked at all wavelengths)-type II

Level of obscuration connected to viewinginclination

Presence of powerful relativistic (radio) jets Radio-loud AGN : generate powerful jets,

seen principally via synchrotron radiation inthe radio band

Radio-quiet AGN : lack powerful jets(often possess weak jets)

Fundamental parameter controlling jetproduction unknown (maybe black holespin; or magnetic field configuration)

K. Murphy

Model Of Central Region ofAGN

Source Distance from central source

X-Ray Fe Kα 3-10 RS Broad-Line Region 600 RS Megamasers 4 ×104 RS Gas Dynamics 8 ×105 RS Stellar Dynamics 106 RS

Rs= Schwarschild radius=2GM/c2

Rs=1.4x1013M8cm; Rs/c~500M8 sec

The Dark Side ofAGN

• Many AGN are obscured-obscuring material is of severaltypes– Located in the ISM of the

host galaxy– A wind associated with the

AGN– Perhaps a ‘obscuring torus’– Etc– Lack of uniform sample not

sensitive to absorption oremission from this structurehas limited knowledge oftrue distribution ofproperties

physical conditions in obscuringregions are not the same fromobject to object - can be complexwith large and unpredictable effectson the spectrum

AGN Zoo

• In a simpleunification scenariobroad-lined (Type 1)AGN are viewedface-on

• narrow-lined (Type2) AGN– the broad emission

line region (BELR)the soft X-rays andmuch of theoptical/UVemission from theAccretion Disk arehidden by the dust

• However there areother complicationslike jets and a rangein the geometry

• 'Radio loud'objects- e.g. withstrong jets and/orluminous extendedradio emission lieONLY in ellipticalgalaxies!

AGN TypesBroad line (type-1) objects

'Blue' optical/UVcontinuum

Broad optical/UV lines Emission lines from

permitted (notforbidden)transitions

Photoionized mattern>109cm-3

FWHM~2000-20,000 km/s

Narrow optical/UVlines Emission lines from

both permitted andforbidden transitions

FWHM~500km/s Spatially resolved

0.1-1kpc

Seyfert 1 galaxyIRAS 05218-1212

(Trippe et al. 2011)

Ηβ, [OIII], [NII],Hα

• AGN (type I) opticaland UV spectraconsist of a 'featureless continuum' withstrong 'broad' linessuperimposed

• Typical velocitywidths (σ, theGaussian dispersion)are ~2000-5000km/sec

• The broad range ofionization is due tothe 'photoionzation'of the gas- the gas isnot in collisionalequilibrium

• At short wavelengthsthe continuum isthought to be due tothe accretion disk

Van den Berk et al 2001

Origin of λ>4000Å continuum not known

Cut off due to abs by Heither in host galaxy or IGM

Accretion disk light

AGN TypesNarrow line (type-2) objects Reddened Optical/UV continuum Optical Emission line spectrum

“Full light” spectrum only shows narrow(~500km/sec) optical/UV lines

Broad optical/UV lines seen in polarized light…shows that there is a hidden broad line region seenvia scattering (Antonucci & Miller 1985)

X-ray spectrum usually reveals highly absorbednucleus (NH>1022cm-2)

Intermediate type objects (type-1.2, 1.5, 1.8, 1.9) haveobscurers which become transparent at sufficientlylong/short wavelengths

Objects without aStrong Continuum-

e.g type II

• type II do nothave broad linesand have a weakor absent 'non-stellar'continuum

• Depending onthe type ofsurvey andluminosity range~50% of allAGN are of typeII

type II

AGN typesBlazar

• Featureless(no lines)broad bandcontinuumradio-gammarays

• Thought to bedue toemission fromjet in our lineof sight

• Can be veryluminous

Featurelesscontinuum- highlyvariableγ-ray sources

Not absorbed- orionized absorberoften broad Fe Kline- low energyspectrum withabsorption lines

HighlyAbsorbed-strongnarrow Fe Kline, stronglow Eemissionlines

X-rayProperties

Bl LacBlazars FSRQ

BLRG FR INLRG FR II

Radio Loud(strong jet)-ONLY inELLIPTICALGalaxies

Type I (broadpermitted lines)Seyfert 1QSO

Type II (narrowforbidden lines)Seyfert 2

Radio quiet(weak or no jet)

RadioLoudness

Names and Properties No Lines

• Some of different classes of AGN are trulydifferent ‘beasts’- (e.g. radio loud vs radio quiet)but

• Much of the apparent differences are due togeometry/inclination effects- this is called theUnified Model for AGN (e.g. type I vs Type Iradio quiet objects, blazars - radio loud objectsobserved down the jet)

• The ingredients are: the black hole, accretiondisk, the jet, some orbiting dense clouds of gasclose in (the broad line region), plus a dustytorus that surrounds the inner disk, some lessdense clouds of gas further out (the narrow lineregion) (adapted from T. Treu)

R. Fender 2007

ISCO=innermost stable orbit-disk terminates there

Discovery of black holes

• First evidence for anobject which ‘must’ bea black hole came fromdiscovery of the X-raysource Cygnus X-1– Binary star

system… black holein orbit around amassive O-star;period =5.6 days -not eclipsing

– Mass of x-rayemitting object 7-13M- too high for a NS.Object emits lots ofx-rays little opticallight.

– X-rays produced dueto accretion ofstellar wind from O-star

– 2kpc away

Velocity curve of the stellar companionIt is a massive O star

f(M) = PorbK32 /2πG = M1sin3i/(1 + q)2.

q=M2/M1the value of the mass function is theabsolute minimum mass of the compact star

The Center of the Milky Way

• The center of the MW iscalled Sagitarius A*(SgrA*)from the name of the radiosource at the dynamicalcenter of the MW.

• This is also the location of aweak, time variable x-ray(log Lx~34- 100x less than atypical x-ray binary) and IRsource

• The radio source is verysmall(VLBI)(<0.0005"<50Rs forM=4x106M BH at d=8kpc)

• At SgrA* 1"=0.04pc=1.2x1017

cm ,0.5mas=6AU

Radio image of SgrA*

Radio,nearIR andx-raylightcurves

Some Problems with Sgr A*

• There is lots of gas foraccretion in thegalactic center fromthe ISM and stellarwinds

• Yet the observedluminosity is very low(L/LEdd~ 10-10)

• What happens to theaccretion energy-where does the massand energy go

• Sgr A* is similar to>95% of all massivegalaxies- they have bigblack holes, but lowluminosities TODAY!(AGN evolution)

MW Galactic Center

• galactic centers are 'special' places• MW galactic center

radio

x-ray

Motion of Stars Aroundthe Center of theMilkyway- see

http://www.youtube.com/watch?v=ZDxFjq-scvU

http://www.mpe.mpg.de/ir/GC/

MW Center

• Two teams ledby R. Genzeland A. Ghezhave measuredthe 3-Dvelocities ofindividual starsin the galacticcenter

• This allows adeterminationof the masswithin givenradii

• The inferreddensity of thecentral regionis >1012M/pc3

•As shown by Genzel et al the stability of alternatives to a black hole (darkclusters composed of white dwarfs, neutron stars, stellar black holes or sub-stellar entities) shows that a dark cluster of mass 2.6 x 106 Msun, and density20Msunpc–3 or greater can not be stable for more than about 10 million years

Predicted mass from models of the Milkway

Velocity Distribution of Stars Near theCenter of the MW

Ghez et al 1998

Eckart-

• While stars are moving very fast near the center(Sgr A*) the upper limit on its velocity is 15km/sec

If there is equipartition of momentum between thestars and SgrA* then one expects

M SgrA* >1000M(M*/10M)(v*/1500km/sec(vsgrA*/15km/sec) -1

Where we have assumed thatthe star stars we see have amass 10M and a velocity of1500 km/sec

Schwarzschild and Kerr Metric

• for a Schwarzschild BH the innermost stableradius is 3rG=6GM/c2 - there are no stablecircular orbits at smaller radii– the binding energy from this orbit is 0.0572 of the

rest mass energy• For a Kerr the innermost stable radius is at

r+=GM/c2 The spinning black hole drags thethe inertial frame-

• The smaller critical radius allows more energyto be released by infalling matter– For a Kerr BH, 0.423 of the rest mass energy

can be released.

• There is another 'fiducial' radius in the Kerrsolution, that radius within which all lightcones point in the directon of rotation, the'static' radius, r static.

• Between r static and r+ is a region called the'ergosphere' within which particles must rotatewith the black hole and from energy might beextracted (Penrose process).

Sizes and Time Variability (seeBegelman, Fabian and Rees 2008,

Fabian and Rees 1979)• Assume each emitting region has a size l' in its

co-moving frame and is causally connected over atime Δt' -- implying l' <c Δt'

• In the laboratory frame the time scale is dilated toΓΔt' (Γ=1/sqrt(1-β2); β=v/c

• From an observers point of view the duration isreduced by 1/(1-βcosθ)- in the limit β~1 andθ<1/Γ this is ~2Γ2

• Thus a observed time scale l'<c t varΓ

• Generalized Efficiency argument (similar to theEddington limit)

• the mass required to produce a total amount ofenergy E=ΔLΔt=εMc2 ( ε is the efficiency ofconverting matter to energy)

• This is related to the optical depth τ byM=4R2τmp/σ and the emitted photons emerge on atime scale Δt=R/c(1+τ) − then minimize Δt for agiven mass M

giving ΔL<εc2 Δtmp/σ• which for the Thompson cross section and 10%

efficiency gives∀ ΔL<2x1041ε 0.1Δt ergs/sec

What About Other SupermassiveBlack Holes

• At the centers ofgalaxies- much moredistant than SgrA*

• First idea: look for a'cusp' of stars caused bythe presence of theblack hole- doesn'twork, nature produces alarge variety of stellardensity profiles… needdynamical data

• Dynamical data: use thecollisionless Boltzmaneq (seen this before)

• V=rotational term;velocity dispersion has3 components σr, σφ, σθ

Kormendy and Richstone (2003)

Example of data for thenearest galaxy M31

• Notice the nasty terms• Vr is the rotation

velocity σr σθ, σφ arethe 3-D componentsof the velocitydispersion ν is thedensity of stars

• All of these variablesare 3-D; we observeprojected quantities !

• The analysis is doneby generating a set ofstellar orbits and thenminimizing

• Rotation and randommotions (dispersion)are both important.

• Effects of seeing (fromthe ground) areimportant- Hubbledata

NGC1277- Velocity Data andBH Mass

• Top is rotationcurve vsdistance fromcenter

• Middle isvelocitydispersion vsdistance fromcenter

• Bottom 2 curvesare measures ofthe non-gaussianity ofthe velocityfield (sensitiveto distributionof orbits)