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Quasar Clustering
(A Dabbler’s Perspective)
CCAPP AGN Workshop: Oct. 2, 2007
Adam Lidz (CfA)
Thanks to: Phil Hopkins, Lars Hernquist,
T.J. Cox, and others….
Outline
• Motivation
• Some observational results
• Theoretical modeling
• Synthesis between models and observations
• Let’s discuss how to move forward!
$64K Questions
• Quasar triggering/fueling mechanisms? Tests of the merger
hypothesis. Importance of other fueling mechanisms?
• Quasar lifetimes and lightcurves. Extended or light-bulbs?
• Association with galaxy formation: how are quasar and galaxy
populations related?
• Which dark matter halos host quasars? Are there specific types
of halos that host? Redshift evolution?
• Is black hole growth self-regulated? Nature of regulation:
momentum or energy driven feedback? Does this vary w/ z?
What can we measure?
• Redshift dependence of
clustering.
• Luminosity dependence.
Osmer 81
• Compare quasar clustering
and that of different galaxy
populations. Compare z=0
galaxy populations to high-z
quasar populations.
• Small-scale quasar
clustering.
da Angela et al. (2006)
Redshift Dependence
• Bias is a strong function of z.
• Measurements at all z
consistent with M_halo ~ 4 x
10^12 M_sun/h.
• Shen et al. (2007): roughly
the same M_halo at z > 3.
• Is this a clue?
Hopkins et al.
astro-ph/0611792
Luminosity Dependence
• Observations indicate
little luminosity
dependence, athough
not very strong
statistically.
• Different than e.g.
SDSS red galaxy
populations, naïve
expectations?
Top: Adelberger & Steidel 2005
Bottom: da Angela et al. 2006
Small-Scale Clustering
• Observations show
“excess” clustering on
small-scales?
• Green points from
Hennawi et al. (2005),
blue points from Myers
et al. (2006), plot from
Hopkins et al.
arXiv:0706.1243
Is it “excess” power?
• What is the right “null”
model?
• Z~4 LBG two-point function
also shows strong two-point
correlation function on smallscales. (Ouchi et al. 2005)
[Thanks, Martin!]
• Cooray model reproduces,
but not with a merging
population.
Cooray & Ouchi 2006
Theoretical Models
• Springel, Di Matteo,
Hernquist, Cox, Hopkins, Li,
Robertson, etc… simulations
of major galaxy mergers
including black hole growth.
• Gas-rich major mergers -->
large inflows of gas.
• Black hole is sub-resolution
sink particle that accretes
gas according to BondiHoyle/Eddington limited rate
depending on local gas
density.
Quasar Lifetimes and Lightcurves
• Strong luminosity
evolution with time -extended dim periods,
short duration peak
phases.
• Different than lightbulb,
exponential growth
models.
Hopkins et al.
astro-ph/0504252
Modeling Quasar Abundances
• Simulations of individual mergers give t_life(L|L_peak).
• Need rate of gas-rich major mergers to model abundances.
Either try to predict rate of relevant mergers (Hopkins et al.
2007), or calibrate empirically off of one observation and make
other predictions (Hopkins et al. 2005): dn/dt(L_peak, z).
Hopkins et al. interpretation of
luminosity function
• Extended period at low
luminosities ---> bright and
faint quasars are mostly
similar sources seen at
different stages of their
lifetime.
• Break is set by peak in dn/dt
• Much different than light-bulb
models.
Hopkins et al. 2005
Modeling Quasar Clustering
• Degeneracy from luminosity function alone: are quasars
numerous yet short-lived or rare, yet long-lived? (Martini &
Weinberg 2001, Haiman & Hui 2001). Distinguish with
clustering!
• In merger models, L_peak is correlated with halo mass, but
instantaneous luminosity is not so correlated w/ M_h. Take into
account simulated light curves, correlation + scatter with halomass, and empirical constraints or theoretical predictions for
dn/dt (Lidz et al. 2005):
Luminosity Dependence
• Luminosity dependence of
quasar clustering may offer a
test!
• Dim sources are mostly
similar to bright sources, but
seen in a different phase of
evolution.
• Expect weak luminosity
dependence although some
at high L.
• Scatter in L_p -- M_halo also
washes out b(L).
Lidz et al.
astro-ph/0507361
Luminosity dependence: comparison w/
observations
• Observations favor
weak luminosity
dependence and favor
complex lightcurves,
disfavor lightbulb
models…
• But not a very strong
test so far.
Hopkins et al.
arXiv:0706.1243
Luminosity Dependence and
Fueling Mechanisms
• Future measurements might
turn up signature of nonmerger fueling at very low
luminosity.
• Black dashed show mergertriggering, black solid
includes impact from nonmerger events: stochastic
accretion through collisions
w/ molecular clouds, gas
inflows through bars, etc..
Hopkins et al.
astro-ph/0611792
Comparing with galaxy clustering
•
Quasars generally cluster less
strongly than red, early-type
L_star galaxies, and more
strongly than blue, ~ L_star
late-types.
•
Quasars do not directly trace
late-type star-forming
galaxies. “Intermediate” state
between red and blue
galaxies?
•
At z~2.5, like ULIRGs.
Hopkins et al.
astro-ph/0611792
Clustering of Quasar Descendents
•
b_Q(z_in) --> b(z=0) from
linear theory.
• There is a characteristic
L_star and M_BH at each z.
• M_bh (z=0) = 0.001 M_gal
• Clustering of quasar
“descendents” is consistent
with early-type ellipticals but
not late-types. Progenitors
of early-types hosted
quasars!
Hopkins et al.
astro-ph/0611792
Scale Dependent Bias
• Linear biasing can be a
bad approximation for rare
quasar halos even on
scales where dm is fairly
linear.
• Halos from an N-body
simulation: M=10^1210^13 M_sun at z=3.
Conclusions
• Clustering can help address some of the $64K
questions: host halos, light-curves, role in galaxy
formation/connection with galaxy populations, and
others.
• Quasars appear to reside in halos of M~ 4 x 10^12
M_sun, relatively independent of redshift and
luminosity.
• Thanks!