Active Galactic Nuclei Ay 16, April 8, 2008

AGN DEFINITION PROPERTIES GRAVITATIONAL LENSES BLACK HOLES MODELS

WHAT IS AN AGN? Objects that emit significant amounts of radiation from non-thermal sources (i.e. not stars or dust or thermal gas). In order of discovery: Seyfert Galaxies Radio Galaxies Quasars BL Lac Objects LINERS (Low Ionization Emission Regions)

Early History Carl Seyfert & strange emission line galaxies (1943) Birth of Radio Astronomy & discovery of strong sources = radio galaxies (40-50’s) Greenstein & Schmidt & QSO’s (1963) Surveys of Extremely Blue Objects (60-70’s) Surveys at other Wavelengths (70’s > )

SY1 AGN Spectra SY2 QSO

Mean UV QSO Spectrum

LBQSO Spectrum

NGC 4151 Typical SY1

Seyfert 1 galaxy and quasar spectra are dominated by broad line regions, lines often showing doppler velocities of 0.1c Seyfert 2 galaxies spectra are dominated by narrower lines, ~ km/s wide LINER spectra are dominated by stars plus emission lines from multiple ionization states indicative of non-thermal excitation BL Lac spectra show almost no features but strong continua

M87 Core In X-rays

Markarian 231

Markarian 421 BL Lac in an E Galaxy TeV  Source

BL LAC SED’s

Radio Galaxies M87 = Virgo A

M87 in the Radio (VLA)

M87 Central Jet

M87 Jet In 3 bands

Centaurus A Radio on Optical Image

Cygnus A (VLA Conway & Blanco)

Synchrotron Power  = related to kinetic enegy of electron = (1 - (v/c) 2 ) -1/2 = (1 -  2 ) -1/2 where  = v/c

Synchrotron Spectra

Baldwin, Phillips & Terlevich AGN LINERS NORMAL

Ly Alpha Forest

Eddington Luminosity Largest Luminosity that can pass through a gas in hydrostatic equilibrium : Outward Force of Radiation Pressure > Inward Force of Gravity Gravity dP/dr = -  g = -GM  /r 2 Luminosity dP/dr = -(  T  /m p c) (L/4  r 2 )  T = Thomson Cross section L Edd = 4  GMm p c/  T = 3.3 x 10 4 L  (M/M  )

Gravitational Lensing Deflection of Light passing at a distance b by an object of mass M:  = 4GM/bc 2 Bending of light by the Sun: r = 6.96 x cm M = x g  = 8.47 x radians = 1.74”

Gravitational lensing :

= Einstein’s Cross

Gravitational Redshift Photons lose E as the move out of a gravity well. For a photon E = hc/, “m” = E/c 2 = h/c Gravitational Potential E = -GMm/r  E = -GMh/c r  / = GM/rc 2 which generally is pretty small except for NS and BH

Black Holes Curvature around a point mass has a critical radius = Schwarzchild Radius Inside this is a singularity R S = 2GM/c 2 In units we know R S = 3.0 km (M/M  ) Gravitational redshift from R S = 

NGC 4261 X-ray vs Optical

V = 1100 km/s

M87’s central mass: Given the HST observations, what’s the enclosed mass?  v = 1100 km/s  ~ 1” D = 16.1 Mpc R = kpc (78 pc) GMm/R = 1/2 mV 2 for circular orbits M = 0.5 V 2 R/G G = x kpc (km/s) 2 / M  M core ~ M 

Reverberation Mapping NGC5548

Lag ~ 20 days Size ~ 20 light days ~ 0.02 pc

Maggorian Relation (Nuker team) Almost every large galaxy has a central BH, and the BH mass is directly correlated with the galaxy’s total bulge mass!

A Unified Model of AGN’s We have come to believe that all AGN are essentially driven by the same phenomena --- a central black hole surrounded by an accretion disk, hot clouds of gas and dust. The disk is hot, 10 5 K plus. The AGN is powered by accretion onto the BH. And what you actually see is driven by the viewing angle.

Unified AGN Model BH + Disk + Torus SY2 SY1 BL Lac edge on tilted down the pipe