Transcript Extragalactic Astronomy • First part: Quasars and Active Galactic Nuclei • Some supplemental reading: GREAT compilation of review articles at http://nedwww.ipac.caltech.edu/level5/active_galaxies.html.

Extragalactic Astronomy
• First part: Quasars and Active Galactic Nuclei
• Some supplemental reading: GREAT compilation of
review articles at
http://nedwww.ipac.caltech.edu/level5/active_galaxies.html
Introductions
• 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!
Homework
• Read Introductory material from Peterson:
at http://nedwww.ipac.caltech.edu/level5/Cambridge/frames.html
• 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 [email protected] 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 a=275 AU P=2.8 yr
 2.7 million solar
masses
• Radio image of Sgr A*
about 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 Genzel’s group:
http://www.mpe.mpg.de/www_ir/GC/
The (slightly) active nucleus of our galaxy
• FYI, here is one
of the the
Genzel groups
individual Kband images
taken at high
spatial
resolution
using the
technique of
speckle
interferometry..
Other items from Genzel’s group:
http://www.mpe.mpg.de/www_ir/GC/
Active Galactic Nuclei: AGNs
• A small fraction of
galaxies have extremely
bright “unresolved”
star-like cores (active
nuclei)
• 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 (> 10,000 km/s in lines)
– 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?
3C31
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 don’t have strong
jets. Some quasars clearly have
outflowing winds not well collimated.
• 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_contents.html
Accretion Disks
•
From our text: Horizons, by Seeds
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
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?bibcode=1999PASP..111....1K&db_key=AST&high=3d6571051d23256
• 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 on-line:
– http://www.physics.ucsb.edu/~blaes/habk/
• alpha-disk solutions illustrate some basic physics
and aren’t too complicated. Check out S&S73
• 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 subject:
http://nedwww.ipac.caltech.edu/level5/Sept01/Wilkes/Wilkes_contents.html
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
From Horizons by Seeds
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.
•
“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 Unification.”
• Another nice website:
http://www.mssl.ucl.ac.uk/www_astro/agn/agn_unified.html
Unified Models:
Different Views of the Accretion Disk
The torus of gas and dust can block part of our view
•
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 lines
•
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 view
•
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 lines
•
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 past
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
strongly.
• Can measure orientation by various methods,
e.g., LogR* = core/lobe radio flux at 5 GHz restframe (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 >1 billion solar masses!
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 => Quasars (“quasar epoch” around z=2 to z=3)
• Most galaxies may have massive black holes in them
• They are just less active now because gas supply is less
The AGN “Zoo”
• Quasars (M < -23)
– Radio-Loud
• FR II Radio Galaxies (type 2 quasars)
• Radio-loud Quasars or just Quasars (type 1 quasars)
– Optically violent variables (OVVs)
– Radio-Quiet
• QSOs – type 1 (broad lines) and type 2 (only narrow lines)
– Infrared-Loud – IRAS quasars, Far-IR Galaxies, ULIRGs
• Low Luminosity AGNs (M > -23)
– Radio-Loud
• FR I Radio Galaxies
• Bl Lac objects, AKA Blazars
– Radio-Quiet
• Seyfert Galaxies – type 1 through type 2 (see QSOs)
• LINERs (Low ionization nuclear emission-line regions)
• Shields “A Brief History of AGN” astro-ph/9903401
Surveys/Catalogs
• SEDs immediately show AGNs don’t 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/catalogues/veron2_9/veron2_9.html
• Hewett & Foltz (1994) on Quasar Surveys:
http://nedwww.ipac.caltech.edu/level5/Hewett/frames.html
• My NSF proposal focuses on “physical” samples.
AGN Emission Lines
• Hagai Netzer’s section in Saas-Fee Advanced
Courses 20, 1990, available online:
– http://nedwww.ipac.caltech.edu/level5/March02/Netzer/Netzer_contents.html
• 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)
• AO…sort 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: “StarburstQuasar”
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
2001):
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.caltech.edu/level5/Sept01/Peterson2/Peter_contents.html
Taking a step back to fundamentals:
Arguments 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 < 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 Institute’s 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 ΔV2 / G)
– r = scale length of region
– ΔV 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
X-ray Fe Kα
Broad-Line Region
Megamasers
Gas Dynamics
Stellar Dynamics
Radius
3-10 Rs
600 Rs
4x104 Rs
8x105 Rs
106 Rs
Where Schwarzschild radius Rs = 2GM/c2 = 3x1013 M8 cm
Reverberation Mapping (RM)
Kaspi et al. (2000) studied bright PG
quasars, particularly Hβ, finding that
R=32.9(λLλ5100/1044 erg s-1)0.7 lt-days
For the Hβ 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?
Ferrarese et al. (2001)
• RM-derived masses
follow the same Msigma 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
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)/4πR2nHc ~ 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 Hβ
• Single epoch L vs. mean L
Vestergaard (2002)
• Single epoch BH Mass vs. RM BH mass
Vestergaard (2002)
• Extend Calibration to UV Line CIV λ1549
• This is a calibrated C IV Black Hole Mass – not wholly
independent – should be tested at high-z, high-L
Brotherton & Scoggins (2004)
• Hβ 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)
• Hβ 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 σ*
• 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, right?
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”
• I’ll look for more
recent pictures