ACTIVE%20GALACTIC%20NUCLEI%20and%20UNIFICATION%20SCHEMES

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ACTIVE GALACTIC NUCLEI and UNIFICATION SCHEMES

• Paul J. Wiita
• Georgia State University, Atlanta, USA
• Winter School on Black Hole Astrophysics
• APCTP, Pohang, January 17-20, 2006

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Outline

• Observational classification peculiar vs. active
  galaxies
• Key properties of different AGN classes
• Fundamental reasons for SMBH model
• Microvariablity of Different AGN types
• Unification schemes for AGN

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Start with the Mildly Active or Peculiar Galaxies

• STARBURST galaxies -- 100's of stars forming per
  year, but spread over some 100's of parsecs.
• Other PECULIAR galaxies involve collisions or
  mergers between galaxies.
• Sometimes produce strong spiral structure (e.g.
  M51, the "Whirlpool")
• Sometimes leave long tidal tails (e.g. the
  "Antennae" galaxies)
• Sometimes leave "ring" galaxy structures--an E
  passing through a S.

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Peculiar Galaxies Starburst (NGC 7742) ,
Whirlpool (M51), Antennae (NGC 4038/9) in IR,
Ring (AM 0644-741)
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Colliding Galaxies

• Cartwheel ring galaxy
• Antennae, w/ starbursts and a simulation a
  collision in progress

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4 MAIN CLASSES of REAL AGN

• Radio Galaxies
• Quasars
• Seyfert Galaxies
• BL Lacertae Objects (now more often called
  Blazars with some Quasars included)
• All are characterized by central regions with
  NON-THERMAL radiation dominating over stellar
  (thermal) emission

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Thermal vs. Non-Thermal Spectra Normal
galaxy spectra arise from stars, AGN mostly
synchrotron and inverse Compton
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RADIO GALAXIES

• All (nearly) are in Elliptical galaxies, usually
  giant Es
• Two oppositely directed JETS emerge from the
  galactic nucleus
• They often feed HOT-SPOTS and and LOBES on either
  side of the galaxy
• Radio source sizes often 300 kpc or more --- much
  bigger than their host galaxies optical extents.
  
• Head-tail and wide-angle-tail radio galaxies
  arise when jets are bent by the ram-pressure of
  ICM/IGM gas as the host galaxy moves through it.
• For powerful sources only one jet is seen this
  is because of RELATIVISTIC DOPPER BOOSTING the
  approaching jet appears MUCH brighter than an
  intrinsically equal receding jet since moving so
  FAST
• Can yield CORE DOMINATED RGs

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Radio Galaxy Centaurus A
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Cygnus A and M87 Jet
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M87 on all Scales1.3cm VLBI down to 0.07
pc(100 RS) while 90 cm VLA shows bubbles out to
70 kpc
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Radio Lobes Can Dwarf Big Host Galaxies

• Fornax A, about 400 kpc across
• 3C 296, about 150 kpc across (VLA images)

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Fanaroff-Riley Classification

• FR I RGs (M87) are weaker and have the peak of
  their flux from the inner portion (often jet or
  plume dominated) 3C 31 (VLA 20 cm)
• FR II RGs (most previous) are more powerful,
  possess hot-spots and dominated by the extended
  lobes
• LR from 1041 to 1046 erg/s

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More FR I RGs3C75 3C449 3C83.1 (at 6 and 20
cm from VLA)
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Ledlow-Owen Relation FR II/I

• Greater radio luminosity needed to make an FR II
  if the jets emerge from a more luminous host
  galaxy
• Probably implies many FR IIs turn into FR Is if
  they entrain too much gas and slow from
  relativistic speeds

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Core Dominated RG (M86)
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Doppler Boosting and Apparent Velocity

• Dramatic increases in observed flux density if
  jet has high v ?c and small l-o-s angle, ?.
• Superluminal apparent transverse velocities also
  seen frequently in VLBI measurements of knots

Doppler factor, ? Lorentz factor, ? and spectral
index,? Exponent 3 for knots, 2 for continuous
flow
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QUASAR PROPERTIES

• QUASI-STELLAR-OBJECT (QSO) i.e., it looks like
  a STAR BUT NON-THERMAL SPECTRUM ?UV excess (not
  like a star)
• BROAD EMISSION LINES ? Rapid motions
• VERY HIGH REDSHIFTS ? not a star, but FAR away.
  The current (2005) convincing record redshift is
  z 6.5, i.e., light emitted in FAR UV at 100 nm
  is received by us in the near IR at 750 nm
• HUGE DISTANCES ? VERY LUMINOUS

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NEWER QUASAR DISCOVERIES

• Only about 10 are RADIO LOUD
• Most show some VARIABILITY in POWER
• OVV (Optically Violently Variable) QUASARS change
  brightness by 50 or more in a year and are
  highly polarized (gt 3 linear in optical)
• QUASARS are AGN surrounding galaxies detected,
  though small nucleus emits 10-1000 times
  MORE light than 1011 stars! Brighter than a
  TRILLION suns
• Lbol gt 1046 erg/s would qualify as a quasar

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Quasar 3C 273

• Radio loud
• Rare OPTICAL jet, but otherwise looks like a star
• Relatively nearby quasar

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Redshifted Spectrum of 3C 273
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Typical Quasar Appearance

• Most are actually very faint
• BUT their huge redshifts imply they are billions
  of light-years away and intrinsically POWERFUL

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Quasar Host Galaxies

• Even by z 3 many
• QSOs were in forming galaxies with multiple
  components
• Most quasar host galaxies have MBlt-23 and are
  extremely luminous themselves

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Radio Loud Quasar, 3C 175
Most quasars do vary with most changing
noticeably over the course of a year or
less. These rapid variations imply small
sizes. Immense powers emerging from a volume
smaller than the solar system.
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Quasar Emission Lines

• Broad emission lines have FWHM gt 5000 km/s
• Usually have narrow cores w/ FWHM lt 2000 km/s
• Diagnostics of T and density, implying TBLR ?
  15000 K and 108 lt n lt 1012 cm-3 for BLR
• Breadth implies lines form from rapidly moving
  gas clouds at lt 1 pc from core, random or in
  disk wind
• Lower ionization state of NELs implies at much
  greater distance from the ionizing core of AGN
  100 pc
• Locations of BLR and BH mass can come from
  reverberation mapping line variability lags
  continuum

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SEYFERT GALAXIES

• Sa, Sb galaxies (sometimes S0) with BRIGHT,
  SEMI-STELLAR NUCLEI
• NON-THERMAL STRONG EMISSION LINES
• VARIABLE in lt 1 yr ? COMPACT CORE
• Type 1 Broad Emission lines (like QSOs), strong
  in X-rays LX gt 1043 erg/s
• Type 2 Only narrow Emission lines, weaker in
  optical continuum and X-rays LX gt 1041 erg/s
  (observed)
• Occasionally one type evolves into another over a
  few years -- indicative of viewing along edge of
  screen
• Type 2 are 2 to 3 times more common than Type 1

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LIFETIMES OF SEYFERT GALAXIES

• About 1 of all Spirals are SEYFERTS, so
• Either 1 of all S's are always Seyferts OR
• 100 of S's are Seyferts for about 1 of the time
  (MORE LIKELY active lifetimes 108 yr )
• OR 10 of S's are Seyferts for about 10 of the
  time (or any other combination of fraction and
  lifetime)

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A Seyfert and Variability

• Circinus, only 4 Mpc away 3C 84

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More About Seyferts

• Seyferts are usually weak radio emitters.
• CONCLUSIONS ABOUT SEYFERTS Fundamentally, they
  are WEAKER QSOs
• Type 1 we see the center more directly Type 2
  dusty gas torus blocks view of the center and
  more reradiated IR is seen

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BL Lacertae Objects

• NON-THERMAL SPECTRUM Radio through X-ray (and
  gamma-ray)
• Radiation strongly POLARIZED
• HIGHLY VARIABLE in ALL BANDS
• But (when discovered) NO REDSHIFT, so distances
  unknown
• Later, surrounding ELLIPTICAL galaxies found
• CONCLUSION greatly enhanced emission from the
  AGN due to RELATIVISTIC BOOSTING of a JET
  pointing very close to us.
• BL Lacs OPTICALLY VIOLENTLY VARIABLE QUASARS
  HIGHLY POLARIZED QUASARS ARE OFTEN CALLED BLAZARS

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Optical Monitoring Blazar Light Curve
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AGN CONTAIN SUPERMASSIVE BLACK HOLES (SMBHs)

• KEY LONGSTANDING ARGUMENTS
• ENERGETICS Powers up to 1048 erg/s (1041W) Even
  at 100 efficiency would demand conversion of
  about 18 M? /yr ( ) into energy.
• Nuclear processes produce lt 1 efficiency.
• GRAVIATIONAL ENERGY via ACCRETION can produce
  between 6 (non-rotating BH) and 32
  (fastest-rotating BH),and the Luminosity is
  crudely
• L G MBH / R,
• with R the main distance from the Super Massive
  Black Hole (SMBH) where mass is converted to
  energy.

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Reminder Orbits around BHs

• GR gives rise to an effective potential which
  yields orbits depending on the energy and angular
  momentum of the matter near a BH
• Once beyond about 50 Rs orbits are Newtonian
• Unlike Newtonian case we find an innermost stable
  orbit at Rms3Rs 6GM/c2 for Schwarzschild BH
  
  There is also the last possible, or
  marginally bound, orbit at Rmb2Rs (where
  accretion efficiency 0)
• A pseudo-Newtonian potential ?GM/(r-RS)
  reproduces the above results (Paczynski Wiita)
  
• If we look for orbiting photons, instead of
  massive particles, there is a last stable orbit
  at Rph1.5Rs

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Kerr(-Newman) Black Holes

• Rotating BH key results are the presence of a
  static limit, inside of which one must co-rotate
  with the BH
• The horizon moves further inward the faster the
  BH spins. This implies Rms and Rmb also move
  inward.
• The amount of binding energy that is extracted
  from infalling matter goes up from lt0.06 to 0.42
  m(c2)

Cosmic censorship hypothesis
a lt M so no naked singularities
exist
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Time Variability

• tVAR R / c
• tVAR 104 s ?
• R 3 x 1014 cm 10-4 pc
• For L 1047 erg/s,
• 10 M? /yr we get MBH 3 x 108 M? and RS
  9 x 1013 cm
• So, R 3 RS
• MUTUALLY CONSISTENT POWERS AND TIMESCALES.

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Big Blue Bump in QSO SED

• This peak is commonly seen in the blue/Near UV
  (restframe) for quasars and is nicely modeled by
  the quasi-thermal emission from a disk accreting
  at substantial rates (T50,000 K) composite of
  2200 (!) SDSS quasars (Vanden Berk et al 2001)

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RECENT OBSERVATIONAL SUPPORT

• The Hubble Space Telescope has revealed that star
  velocities rise to very high values close to
  center of many galaxies and gas is orbiting
  rapidly, e.g. M87, but dozens of cases now known
• Disks have been seen via MASERS in some nearby
  Seyfert AGN.
• VLBI radio jets formed within 1 pc of center, as
  seen earlier for M87.

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Rapidly Rotating Gas in M87 Nucleus
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Direct Evidence for Rotating Disk
Masers formed in warped disk in NGC 4258 (and a
few other Seyfert galaxies)
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Evidence for Supermassive Black Holes
NGC 4261 at core of radio emitting jets is a
clear disk 300 light-yrs across and knot of
emission near BH
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Similar Optical Microvariability in Radio Quiet
QSOs and Blazars?

• Lots of debate about RQQSOs some claimed fairly
  frequent detections of INOV (e.g. de Deigo et al.
  1998) others say no (e.g. Rabette et al. 1998
  Romero et al. 1999) but temporal sampling and/or
  sensitivity and/or comparison choices were
  inadequate
• We claim the first convincing evidence for such
  optical INOV in true radio silent quasars
  (Gopal-Krishna et al. 2003 Stalin et al.
  2004a,b Sagar et al. 2004)
  Observations mostly at
  104cm telescope, Nainital, India
• Both duty cycle and amplitude are lower in RQQSOs
  than for blazars but differences between RQQSOs
  and radio-loud quasars (and even low-polarization
  core-dominated quasars) are small in our matched
  sets of 6 or 7 of each type of AGN
• Differences observed can arise from simple
  Doppler boosting

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RQQSO INOV
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BL Lac INOV
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Radio-Loud Lobe Dominated Quasar INOV
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Comparison of RQQ and BL Lac INOV

• Duty cycles for low amplitude variations are very
  similar, around 20
• High amplitude variations all BL Lac

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Comparison of CDQ and BL Lac INOV

• Low polarization CDQs have properties similar to
  RQQs and LDQs, with duty cycles of 10-25
  when observed for gt 4 hours
• High polarization CDQ is similar to BL Lacs, with
  duty cycles gt50

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Doppler Boosting Factors

• Typical INOV amplitude from blazar at small angle
  is converted to lower amplitude and longer
  timescale at larger viewing angles and would
  appear just like RQQSO INOV?similar mechanism.
• Is an optically emitting jet always present?
• Do disk perturbations get amplified in a jet?

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SMBH Model for AGN
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Most (all?) Galaxies Have Central SMBHs
Roughly, SMBH mass is 0.003 of the BULGE mass
for ellipticals, the bulge mass is the entire
star mass for most spirals, just a fraction. So
BH and galaxy probably grow up together. Better
correlation with bulge velocity dispersion or
perhaps galactic potential energy.
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Wide Span of SMBH Mass vs Galaxy Velocity
Dispersion

• Compiled by Greene Ho -- includes active and
  inactive galaxies
• MBH f R V2/G with f0.75 for spherical BLR
• RBLR ? L51000.64
• V from FWHM(H?)
• Best fit M ? ?3.65 for all while M ? ?4.02
  for inactive only

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Unification through Orientation

• For Seyferts scattered BL and continuum can be
  seen in polarized light for Type 2s (Antonucci
  Miller)
• For RGs quasars are shorter than similar powered
  and redshifted FR IIs (Scheuer Barthel
  Gopal-Krishna et al)
• FR I RGs are statistically the parent population
  of BL Lacs for the BL Lacs w/in a few degrees of
  l-o-s (Padovani Urry)

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Seyferts and Unification

• Narrow line spectrum of Seyfert 2
• But, when polarized radiation observed, broad
  lines, scattered by electrons are also visible
• Also explains much lower x-ray and continuum in
  Sy2

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UNIFIED MODELS FOR AGN

• Three main parameters MBH, , and viewing
  angle to the BH and accretion disk axis, ?
• Main ingredients
• SMBH gt 106 M?
• 10-5 pc lt accretion disk lt 10-1 pc (AD)
• broad line clouds lt 1 pc (BLR)
• thick, dusty, torus lt 100 pc
• narrow line clouds lt 1000 pc (NLR)
• sometimes, a JET (usually seen from lt 102 pc to
  maybe 106 pc!)

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Unification for Radio Quiet and Radio Loud

• RADIO LOUD (Jets)
• High MBH,
• ? very small Optically Violently Variable Quasar
  
• ? small radio loud quasar (QSR)
• ? large classical double radio galaxy (FR II
  type)
• Low MBH.
• ? very small BL Lac object
• ? small broad line radio galaxy (FR I type)
• ? large narrow line radio galaxy

• RADIO QUIET
• High MBH,
• ? small QSO is seen including AD and BLR
• ? large only NLR plus radiating torus seen as
  UltraLuminous InfraRed Galaxies (ULIRGs)
• Low MBH,
• ? small Seyfert Type 1 ? big Seyfert Type 2

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Different AGN from Different Angles
If jets are important BL Lacs (and OVVs) along
jet axis, RLQSO at modest angles Radio Galaxies
at larger angles No jets Luminous Quasars seen
close to perpendicular to disk and Ultraluminous
Infrared Galaxies near disk plane Weaker Type 1
or Type 2 Seyferts
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Key Conclusions

• AGN make up a small fraction of galaxies at any
  given time, though all may have undergone such a
  phase when young
• SMBHs provide the ultimate energy source for AGNs
  (masses 106 to gt109M?)
• The zoo of AGN types can be tamed through unified
  schemes (though complications, such as critical
  angle rising with central luminosity are probably
  needed)