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Extragalactic Astronomy


Extragalactic Astronomy – PowerPoint PPT presentation

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Title: Extragalactic Astronomy

Extragalactic Astronomy
  • First part Quasars and Active Galactic Nuclei
  • Some supplemental reading GREAT compilation of
    review articles at http//nedwww.ipac.caltech.edu/

  • Who am I???
  • See http//www.mikebrotherton.com and
    http//physics.uwyo.edu/mbrother for information
    about me and course materials.
  • Who are you???
  • Tell me what you want to learn!

  • Read Introductory material from Peterson at
  • Make your own redshift vs. magnitude diagram of
    quasars from the Sloan Digital Sky Survey (hint
    google sdss quasar catalog) and be able to
    discuss it
  • Email me at mbrother_at_uwyo.edu if you have
    questions or need help
  • Deadline Tuesday, October 14, 2008

Quasars and Active Galactic Nuclei (AGNs)
  • What are they?
  • Observational Properties
  • Standard Model
  • Continuum, Lines, etc.
  • How are they found?
  • A variety of survey types, a zoo of AGNs
  • Orientation and Unified Models
  • How do they evolve?
  • Strongly!
  • Quasar Black Hole Masses
  • Broad Absorption Line Quasars
  • Relationship with their host galaxies
  • Host galaxies
  • Mutual Evolution?

The (slightly) active nucleus of our galaxy
  • Probable Black hole
  • High velocities
  • Large energy generation
  • At a275 AU P2.8 yr ? 2.7 million solar masses
  • Radio image of Sgr Aabout 3 pc across, with
    model of surrounding disk

From Horizons, by Seeds
The (slightly) active nucleus of our galaxy
  • The Genzel et al. movie based on NIR speckle
    interferometry of the Galactic core.
  • Basic orbital mechanics confirm, to high
    precision, a mass of 2.6 million solar masses
    that the stars are orbiting.
  • X-ray flaring also seen.

Other items from Genzels group
The (slightly) active nucleus of our galaxy
  • FYI, here is one of the the Genzel groups
    individual K-band images taken at high spatial
    resolution using the technique of speckle

Other items from Genzels group
Active Galactic Nuclei AGNs
  • A small fraction of galaxies have extremely
    bright unresolved star-like cores (active
  • Shown here is an HST image of NGC 7742, a
    so-called Seyfert galaxy after Carl Seyfert who
    did pioneering work in the 1940s (you might look
    up his original papers).

NGC4151 with a range of exposures
Spectra of Stars, Spectra of AGNs
Average quasar, from Brotherton et al. (2001)
Stars from Horizons by Seeds
Active Galactic Nuclei AGNs
  • Small fraction of galaxies have extremely bright
    unresolved star-like nuclei
  • Very large energy generation
  • Brightness often varies quickly
  • Implies small size (changes not smeared out by
    light-travel time)
  • High velocities often seen (gt 10,000 km/s in
  • Emission all over the electro-magnetic spectrum
  • Jets seen emerging from galaxies
  • Think about the implications of jets.
    Timescales, angular momentum. What do they imply?

Red radio Blue visible
Many Views of Radio Galaxy Centaurus A
Many Views of Active Galaxy Centaurus A
Quasar Images 1
Theoretical Paradigm
  • Supermassive black hole (millions to billions of
    solar masses)
  • Powered by an accretion disk.
  • Jet mechanisms proposed, but very uncertain.
    Most quasars dont have strong jets. Some
    quasars clearly have outflowing winds not well
  • Also, an obscuring torus seems to be present.
    (Unified models apply here.)

AGN Accretion
  • Old (1978!) basic accretion review paper
  • http//nedwww.ipac.caltech.edu/level5/Rees3/Rees_c

Accretion Disks
  • Black hole is active only if gas is present to
    spiral into it
  • Isolated stars just orbit black hole same as they
    would any other mass
  • Gas collides, tries to slow due to friction, and
    so spirals in (and heats up)
  • Conservation of angular momentum causes gas to
    form a disk as it spirals in

From our text Horizons, by Seeds
AGN Accretion Disks
  • Modern disk paper with AGN application, Koratkar
    and Blaes (1999), review in PASP
  • http//adsabs.harvard.edu/cgi-bin/nph-bib_query?bi
  • Basic ideas follow from Shakura and Sunyaev
    (1973) standard alpha thin disks, plus
    relativity, vertical disk structure, non-LTE,
    Comptonization, etc. The models of Hubeny et al.
    (2000) are the most advanced and available
  • http//www.physics.ucsb.edu/blaes/habk/
  • alpha-disk solutions illustrate some basic
    physics and arent too complicated. Check out
  • My post-doc Shang and I fit these models to real
    AGN SEDs. See these at the Wyoming AGN group
    webpage at http//physics.uwyo.edu/agn

Malkan (1983) Fitting the Big Blue Bump with a
power-law plus an accretion disk model using
three temperature zones
Quasar Spectral Energy Distributions (SEDs)
  • Very nice and relatively brief review article
    from Quasars and Cosmology conference by
    Belinda Wilkes (CfA), a world expert on the
  • http//nedwww.ipac.caltech.edu/level5/Sept01/Wilke
  • Must account for physical processes producing
    prodigious luminosity from radio wavelengths
    through the X-ray and even gamma ray regimes.
  • Particular features of interest include
    radio-jets and the radio-quiet vs. radio-loud
    dichotomy, the big blue bump that produces the
    optical/UV energy peak and is thought to arise
    from an accretion disk, and the far infrared that
    represents re-radiation by hot dust.

Quasar Spectral Energy Distributions (SEDs)
  • Wilkes (1997)

3C 273
Orientation and Unified Models
As we have discussed, inner AGN structure
believed to feature a black hole fed by an
accretion disk. Jets may emerge along the spin
axis, and the disk illuminates BLR and NLR
clouds. A dense molecular torus exists on larger
scales and can obscure the central engine from
certain lines of sight.
From Horizons by Seeds
  • Unified Models explain some of the different
    classes of AGN, particularly type 1 and type 2
    Seyferts, via orientation.
  • For specifics, see the Annual Reviews article by
    Antonucci, 1993, a bishop in the Church of
  • Another nice website http//www.mssl.ucl.ac.uk/ww

Unified Models Different Views of the
Accretion Disk
  • The torus of gas and dust can block part of our
  • Seyfert 2 galaxies Edge on view Only gas well
    above and below disk is visible See only
    slow gas ? narrow emission lines
  • Seyfert 1 galaxies Slightly tilted view Hot
    high velocity gas close to black hole is
    visible High velocities ? broad emission
  • BL Lac objects Pole on view Looking right
    down the jet at central region Extremely
    bright vary on time scales of hours
  • Quasars Very active AGN at large
    distances Can barely make out the galaxy
    surrounding them Were apparently more common
    in distant past

From our text Horizons, by Seeds
Spectral differences in Seyferts
Different Views of the Accretion Disk
  • The torus of gas and dust can block part of our
  • Seyfert 2 galaxies Edge on view Only gas well
    above and below disk is visible See only
    slow gas ? narrow emission lines
  • Seyfert 1 galaxies Slightly tilted view Hot
    high velocity gas close to black hole is
    visible High velocities ? broad emission
  • BL Lac objects Pole on view Looking right
    down the jet at central region Extremely
    bright vary on time scales of hours
  • Quasars Very active AGN at large
    distances Can barely make out the galaxy
    surrounding them Were more common in distant

Radio Source Unification
  • Core-dominant sources are seen jet-on, have flat
    radio spectra, and are variable, optically
    polarized and beamed.
  • Lobe-dominant sources are not very variable, have
    steep radio spectra dominated by optically thin
    synchrotron emission, and are not beamed
  • Can measure orientation by various methods, e.g.,
    LogR core/lobe radio flux at 5 GHz rest-frame
    (Orr Browne 1982), also Rv which normalizes
    core flux with an optical magnitude (Wills and
    Brotherton 1995).

Radio Source Unification
Core dominant
Lobe dominant
  • From Wills and Brotherton (1995), plotting Log R
    (which is rest-frame 5 GHz) core to lobe flux
    ratio), vs. the jet angle to the line of sight
    where the jet angle is estimated from VLBI
    superluminal motion.

What makes an AGN active?
  • Need a supply of gas to feed to the black hole
  • (Black holes from 1 million to gt1 billion solar
  • Scales as a few percent of galaxy bulge mass.)
  • Collisions disturb regular orbits of stars and
    gas clouds
  • Could feed more gas to the central region
  • Galactic orbits were less organized as galaxies
    were forming, also recall the hierarchical
    galaxy formation
  • Expect more gas to flow to central region when
    galaxies are young gt Quasars (quasar epoch
    around z2 to z3)
  • Most galaxies may have massive black holes in
  • They are just less active now because gas supply
    is less

The AGN Zoo
  • Quasars (M lt -23)
  • Radio-Loud
  • FR II Radio Galaxies (type 2 quasars)
  • Radio-loud Quasars or just Quasars (type 1
  • Optically violent variables (OVVs)
  • Radio-Quiet
  • QSOs type 1 (broad lines) and type 2 (only
    narrow lines)
  • Infrared-Loud IRAS quasars, Far-IR Galaxies,
  • Low Luminosity AGNs (M gt -23)
  • Radio-Loud
  • FR I Radio Galaxies
  • Bl Lac objects, AKA Blazars
  • Radio-Quiet
  • Seyfert Galaxies type 1 through type 2 (see
  • LINERs (Low ionization nuclear emission-line
  • Shields A Brief History of AGN astro-ph/9903401

  • SEDs immediately show AGNs dont look like stars
  • Selection by optical colors works (e.g., Sloan is
    best, http//www.sdss.org, also 2dF
    http//www.2dfquasar.org )
  • Mutliwavelength works (e.g., radio, X-ray, IR,
    plus optical)
  • E.g., FIRST Bright Quasar Survey
  • Also possible to find via
  • Variability (e.g., MACHO)
  • Proper Motion (lack thereof)
  • Grism Surveys (e.g., Large Bright Quasar Survey)
  • Older compilation catalogs like that of
    Veron-Cetty and Veron (2000) are being surpassed
    by SDSS and 2dF. http//www.obs-hp.fr/www/catalogu
  • Hewett Foltz (1994) on Quasar Surveys
  • My NSF proposal focuses on physical samples.

AGN Emission Lines
  • Hagai Netzers section in Saas-Fee Advanced
    Courses 20, 1990, available online
  • http//nedwww.ipac.caltech.edu/level5/March02/Netz
  • Classic textbook on photoionization is AGN2 by
    Don Osterbrock, popular public tool is CLOUDY by
    Gary Ferland (http//thunder.pa.uky.edu/cloudy/
    ). Section 9.1.2 in Combes et al.

Basically, treat ionization state,
heating/cooling balance, and relate emission line
ratios to metallicity, density, ionizing
continuum, etc. Note LOC models (Baldwin et
al. 1996).
AGN Emission Lines
From Netzer et al. 1994 (I did the figures), on
the SED and unusual emission line profiles of the
OVV 3C 279. Note the steep power-law spectrum.
Optically polarization is high. There is optical
beamed synchrotron radiation in this source. In
many quasars, the emission line profiles are
similar from line to line (consistent with
optically thick BLR clouds). Not so for all
objects, and especially important for figuring
out BLR kinematics and dynamics (which is still
not so clear).
Quasar Host Galaxies
  • Hard to see. Why?
  • How can you do it?
  • HST (Bahcall, others)
  • Near Infrared (eg., McLeod et al. 1996)
  • AOsort of. Issues here.
  • What are their properties? Are they related in
    any way to the activity?
  • Very little known before advent of HST, AO, and
    large near-IR detectors. Still a challenging
    type of observation.
  • Initially thought (based on Seyfert galaxies and
    radio galaxies) that radio properties were
    related to host type. Seems to have been a
    selection effect.

Quasar Images II
Quasar Images III Starburst-Quasar
From Brotherton et al. (1999).
Ties to Host Galaxy Evolution
  • Quasar, star-formation evolution (from Boyle and
    Terlevich 1998)

Ties to Host Galaxy Evolution
  • Central black hole masses seem to correlate with
    host galaxy magnitude (from McLure and Dunlop

Ties to Host Galaxy Evolution
  • Central black hole masses best correlate with
    host galaxy stellar velocity distribution (from
    Ferrarese 2000)

Reverberation mapping yields AGN black hole
masses. A good recent review is by Peterson.
More slides on this ahead! http//nedwww.ipac.cal
Taking a step back to fundamentalsArguments for
Black Holes in AGNs
  • Energy Considerations
  • Nuclear luminosities in excess of 1013 suns
  • Gravitational release capable of converting on
    order 10 rest mass to energy
  • Rapid Variability
  • Timescales lt 1 day imply very small source
  • Radio Jet Stability implies large, stable mass
    with large angular momentum

Measuring Black Hole Masses in Nearby Galaxies
  • SgrA in the Milky Way
  • Water Masers in NGC 4258, a few others
  • Spatially Resolved Gas or Stellar Dynamics Using
    the Hubble Space Telescope (HST)

Max Planck Institutes Galactic Core Group
This plot shows the quantitative limits.
Water Masers in NGC 4258
  • Based on Greenhill et al. (1995)
  • Warped Disk Model
  • Radial Velocities and Proper Motions Measure a
    Mass of 4x107 solar masses (20 times more massive
    than SgrA)

Spatially Resolved Spectroscopy from Space Shows
BH Signatures
  • HST STIS shows evidence for a super massive black
    hole in M84 based on spatially resolved gas
    dynamics (Bower et al 1997). Can also be done by
    examining spatially resolved stellar absorption
    line profiles, plus complex 3D orbital modeling.

The M-sigma Relation
  • Black Hole Masses are about 0.1 of the central
    galactic bulge mass (a big surprise to theorists)
    and tightest correlation is with the stellar
    velocity dispersion (after Gebhardt et al. 2000).

Virial Mass Estimates
  • M f (r ?V2 / G)
  • r scale length of region
  • ?V is the velocity dispersion
  • f is a factor of order unity dependent upon
    geometry and kinematics
  • Estimates therefore require size scales and
    velocities, and verification to avoid pitfalls
    (eg. radiative acceleration).

Potential Virial AGN Mass Estimators
  • Source Radius
  • X-ray Fe Ka 3-10 Rs
  • Broad-Line Region 600 Rs
  • Megamasers 4x104 Rs
  • Gas Dynamics 8x105 Rs
  • Stellar Dynamics 106 Rs
  • Where Schwarzschild radius Rs 2GM/c2 3x1013
    M8 cm

Reverberation Mapping (RM)
Kaspi et al. (2000) studied bright PG quasars,
particularly Hß, finding that R32.9(?L?5100/1044
erg s-1)0.7 lt-days For the Hß emitting gas.
  • Broad lines are photoionized by the central
    continuum, which varies. The line flux follows
    the continuum with a time lag t which is set by
    the size of the broad-line emitting region and
    the speed of light. Recombination timescales are
    very short, BLR stable, and continuum source
    small and central.

Does the BLR obey the Virial Theorem?
  • Four well studied AGNs, RM of multiple emission
    lines shows the expected relationship (slope
    -2) between time lags and velocities (note each
    of the three will have different central black
    hole masses).
  • NGC7469 8.4x106 M
  • NGC3783 8.7x106 M
  • NGC5548 5.9x107 M
  • 3C 390.3 3.2x108 M

Onken Peterson (2002)
Does the BLR obey the Virial Theorem?
  • RM-derived masses follow the same M-sigma
    relationship as seen for normal galaxies that
    have black hole masses measured from HST
    spatially resolved gas or stellar dynamics.
  • Not more points since obtaining sigma for AGN is
    difficult (the AGN dilutes the stellar absorption
    line EWs).
  • Good to 0.5 dex

Ferrarese et al. (2001)
Expect that BLR Scales With Luminosity
  • Photoionization and LOC Models (Baldwin et al.
    1996) suggests that strong selection effects make
    line emission come from same physical conditions
    (same U, n)
  • U Q(H)/4pR2nHc L/nHR2
  • So, for same U, nH, then expect that
  • R L0.5
  • How about in reality?

Empirically BLR Scales With Luminosity
  • Mentioned previously the Kaspi et al. (2000)
    result how R L0.7 (above). In China, Misty
    Bentz of OSU showed that proper correction for
    host galaxy leads to a slope of 0.5! Nice work.
    This permits the possibility of using
    single-epoch measurements to estimate black hole
    masses much easier!

Vestergaard (2002)
  • Single epoch FWHM vs. rms FWHM for Hß
  • Single epoch L vs. mean L

Vestergaard (2002)
  • Single epoch BH Mass vs. RM BH mass

Vestergaard (2002)
  • Extend Calibration to UV Line CIV ?1549
  • This is a calibrated C IV Black Hole Mass not
    wholly independent should be tested at high-z,

Brotherton Scoggins (2004)
  • Hß and C IV Black Hole Mass Comparison
  • All high-z sources very luminous, massive, high
    L/Ledd. Please excuse the color code.

Brotherton Scoggins (2004)
  • Hß and C IV Black Hole Mass Comparison
  • All high-z sources very luminous, massive, high
    L/Ledd. Please excuse the color code.

Using O III FWHM as a Proxy for s
  • Shields et al. (2003).

From Peterson (2002)
Current/future Work Real Astrophysics
  • Black Hole Demographics (growth with z)
  • Is all growth as AGN? Does that produce the mass
    seen in relic black holes at low z?
  • How does the M-sigma correlation arise?
  • That is, how is black hole growth linked to the
    growth of galaxy bulges and star formation?
  • How do AGN behave as a function of mass, L/Ledd,
    viewing angle, etc.?

Quasar Absorption Lines
  • Intrinsic
  • Broad (BALs)
  • Narrow (NALs)
  • Intervening
  • Galactic
  • Lyman alpha
  • Metal line systems

BALQSOs What are they?
  • Are they normal quasars with equatorial winds,
    seen edge-on?
  • Or are they an evolutionary phase?

The AGN H-R Diagram, after Miller 1998
Radio-Loud BALQSOs
  • Originally exclusively radio-quiet, but the first
    radio-loud BALQSOs found by Becker et al. 1997
    and Brotherton et al. 1998. From Becker et al.
    (2000), 90 of the radio-selected BALQSOs are
    compact in FIRST maps (vs. 60 in the non-BAL
    sample), and BOTH steep and flat radio spectra
    are present.
  • Seems to rule out simple orientation schemes,

Radio-Loud BALQSOs
  • BALQSO Spectra from Brotherton et al. 1998.

Another look at the AGN model
  • Not to scale!
  • Probably updated from clouds to flows
  • Ill look for more recent pictures
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