Quasars Probing Quasars:
Shedding (Quasar) Light on
High Redshift Galaxies
Joseph F. Hennawi
UC Berkeley
Ohio State
February 20, 2007
Suspects
QuickTime™ and a
TIFF (Uncompress ed) dec ompres sor
are needed to s ee this pic ture.
Xavier Prochaska
(UCSC)
Scott Burles
(MIT)
Juna Kollmeier (Carnegie) & Zheng Zheng (IAS)
Outline
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•
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Motivation
Finding close quasar pairs
IGM Primer
Quasar-Absorber Clustering
Fluorescent Ly Emission
Bottom Line: The physical problem of a quasar illuminating
an optically thick cloud of HI is very simple compared to other
problems in galaxy formation.
Motivation
A Simple Observation
Spectrum from Wallace Sargent
Quasars Evolution for Poets
Comoving Number Density
Richards
et al. (2006)
Tremaine et al. (2002)
z (redshift)
L*(z)/L*(0)
Boyle et al. (2001)
Dramatic evolution of number
density/ luminosity
nQSO ( L)
look back time
tQSO   
nRelics
Hosts ( M BH )


t H  4 
Quasar Evolution for Pundits
AGN unified model
Barger et al. (2005)
unidentified
BLAGN
Steffen et al. (2003)
non-BLAGN
The AGN unified model breaks down at high luminosities.
“Almost all luminous quasars are unobscured . . . ”
HI in High Redshift Galaxies?
M33 HI/H/Optical
M33 HI/CO
Radial CO and HI profiles for
7 nearby galaxies
(Wong & Blitz 2002).
106 M
3105 M
105 M
Engargiola et al. (2002)
Image credit: Fabian Walter
• The HI is much more extended than the stars and molecular gas.
• Until SKA, no way to image HI at high redshift.
• HI is what simulations of galaxy formation might predict (reliably).
The Power of Large Surveys
Apache Point Observatory (APO)
• Spectroscopic QSO survey
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–
–
–
ARC 3.5m
Jim Gunn
SDSS 2.5m
5000 deg2
45,000 z < 2.2 ; i < 19.1
5,000 z > 3; i < 20.2
Precise (u,g,r, i, z) photometry
• Photometric QSO sample
– 8000 deg2
– 500,000 z < 3 ; i < 21.0
– 20,000 z > 3 ; i < 21.0
– Richards et al. 2004; Hennawi et al. 2006
MMT 6.5m
Follow up QSO pair confirmation
from ARC 3.5m and MMT 6.5m
Finding Quasar Pairs
 = 3.7”
low-z
QSOs
55”
2’
2.0
3.0
2.0
4.0
3.0
Excluded
Area
SDSS quasar @ z =3.13
2.0
4.0
3.0
Cosmology with Quasar Pairs
Close Quasar Pair Survey
Normalized Flux
Ly Forest Correlations
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Discovered > 100 sub-Mpc pairs (z > 2)
Factor 25 increase in number known
Moderate & Echelle Resolution Spectra
Near-IR Foreground QSO Redshifts
45 Keck & Gemni nights. 8 MMT nights
CIV Metal Line Correlations
Keck
Gemini-N
Gemini-S
MMT
Science
 = 13.8”, z = 3.00; Beam =79 kpc/h
Spectra from Keck ESI
Collaborators: Jason Prochaska, Crystal Martin,
Sara Ellison, George Djorgovski, Scott Burles,
Michael Strauss
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Dark energy at z > 2 from AP test
Small scale structure of Ly forest
Thermal history of the Universe
Topology of metal enrichment from
Transverse proximity effects
IGM Primer
Quasar Absorption Lines
•
Ly Forest
– Optically thin diffuse IGM
– / ~ 1-10; 1014 < NHI < 1017.2
– well studied for R > 1 Mpc/h
•
Lyman Limit Systems (LLSs)
– Optically thick 912 > 1
– 1017.2 < NHI < 1020.3
– almost totally unexplored
•
Lyman Limit
Ly
z = 2.96
z = 2.58
Ly
z = 2.96
QSO
z = 3.0
Damped Ly Systems (DLAs)
– NHI > 1020.3 comparable to disks
– sub-L galaxies?
– Dominate HI content of Universe
DLADLA
(HST/STIS)
Moller et al. (2003)
LLS LLS
Nobody et al. (200?)
Self Shielding: A Local Example
Average HI of Andromeda
bump due
LLS
M31 (Andromeda)
DLA
to M33
Ly
forest
Braun & Thilker (2004)
M33 VLA 21cm map
Sharp edges of galaxy disks set by ionization equilibrium with the UV
background. HI is ‘self-shielded’ from extragalactic UV photons.
What if the MBH = 3107 M black hole at Andromeda’s center started
accreting at the Eddington limit? What would M33 look like then?
Proximity Effects
IsolatedQSO
QSOPair
Projected
Neutral Gas
Ionized Gas
• Proximity Effect  Decrease in Ly forest absorption due to large
ionizing flux near a quasar
• Transverse Proximity Effect  Decrease in absorption in background
QSO spectrum due to transverse ionizing flux of a foreground quasar
– Geometry of quasar radiation field (obscuration?)
nQSO
– Quasar lifetime/variability
– Measure distribution of HI in quasar environments
tQSO   
nHosts
t H  4 
Are there similar effects for optically thick absorbers?
Fluorescent Ly Emission
Shielded HI
912 ~ 1 in self
shielding skin
UV Background
   0 e(x
v dist of cloud
P(v)
•
•
•
•
x
2
/2)
 / 
 /c
Only Ly
photons in tail
can escape
Zheng & Miralda-Escude (2002)
In ionization equilibrium ~ 60% of recombinations yield a Ly photon
Since 1216 > 104 912 , Ly photons must ‘scatter’ out of the cloud
Photons only escape from tails of velocity distribution where Ly is small
LLSs ‘reflect’ ~ 60% of UV radiation in a fluorescent double peaked line
Imaging Optically Thick Absorbers
Column Density
Ly Surface Brightness
Cantalupo et al. (2005)
• Expected surface brightness:
SBLy
912


J
20
22  1 z 
 3.7  10 


 4   4 
4
ergs cm-2s-1 "
or Ly  30 mag/ "
• Still not detected. Even after 60h integrations on 10m telescopes!
Sounds pretty hard!
Help From a Nearby Quasar
2-d Spectrum of
Background Quasar
Background
QSO spectrum
11 kpc
r = 15.7!
Wavelength
Transverse flux
= 5700  UVB!
DLA
trough
4 kpc
f/g QSO
extended
emission
Spatial Along Slit (”)
Adelberger et al. (2006)
R = 384 kpc
Doubled Peaked Resonant Profile?
Why Did Chuck Get So Lucky?
b/g QSO
f/g QSO
DLA must be in this
R||
region to see emission
• Surface brightness consistent
with expectation for R|| = 0
• R|| constrained to be very small,
otherwise fluorescence would
be way too dim.
R = 280 kpc/h
If we assume emission was detected at (S/N) = 10, then (S/N) > 1 requires:
R|| < R [(S/N) -1]1/2 = 830 kpc/h or dz < 0.004
Since dN/dz(DLAs) = 0.2, then the probability PChuck = 1/1000!
I should spend less time at Keck, and more time in Vegas $$
Perhaps DLAs are strongly clustered around quasars?
Chuck Steidel
Quasar-Absorber
Clustering
Quasars Probing Quasars
Hennawi, Prochaska, et al. (2007)
Transverse Clustering
Hennawi, Prochaska et al. (2007); Hennawi &
Prochaska (2007)
• 29 new QSO-LLSs with R < 2 Mpc/h
Enhancement over UVB
Chuck’s
object
• High covering factor for R < 100 kpc/h
• For T(r) = (r/rT)-,  = 1.6, and NHI > 1019
cm-2, rT = 9  1.7 (2.9  QSO-LBG)
z (redshift)
 = 2.0
 = 1.6
QSO-LBG
= Keck
= Gemini
= has absorber
= SDSS
= no absorber
Proximate DLAs: LOS clustering
Prochaska, Hennawi, & Herbert-Fort (2007)
• Found 12 PDLAs out of ~ 2000 z < 2.7 quasars
dN
dN
( 3000 km/s)  (1.4  0.3)
dz
dz
• Transverse clustering strength at z = 2.5 predicts that nearly every QSO
should have an absorber with NHI > 1019 cm-2 along the LOS??
• Rapid redshift evolution of QSO clustering compared to paucity of
proximate DLAs implies that photoevaporation has to be occurring.
Photoevaporation
QSO is to DLA . . . as . . . O-star is to interstellar cloud
Cloud survives provided
b/g QSO
f/g QSO
R
1
NH


  500  20.3 -2   1
 10 cm 
nphotons
-2

 2.6  10 4 S56 RMpc
n 1H, -1
nH
Otherwise it is photoevaporated
Bertoldi (1989), Bertodi & McKee (1989)
r = 17
r = 19
r = 21
Hennawi & Prochaska (2007)
nH = 0.1
Proximity Effects: Summary
• There is a LOS proximity effect but not a transverse one.
• Photoevaporation plausible for absorbers near quasars.
• Our measured T(r) gives, PChuck = 1/65.
• Fluorescent emission proves Chuck’s DLA was illuminated.
• Clustering anisotropy suggests transverse systems are not.
• Two possible sources of clustering anisotropy:
– QSO ionizing photons are obscured (beamed?)
– QSOs vary significantly on timescales shorter than crossing time:
tcross ~ 4 105 yr @  = 20” (120 kpc/h).
Current limit: tQSO > 104 yr
Proximity Effects: Open Questions
• Can we measure the average opening angle?
– Yes, but must model photoevaporation assuming an
absorber density profile.
– Much easier for optically thin transverse effect (coming
soon).
• Does high transverse covering factor conflict with
obscured fractions (~ 10%) of luminous QSOs?
• Why did Chuck’s DLA survive whereas others are
photoevaporated?
Fluorescent Ly
Emission
Transverse Fluorescence?
PSF subtracted
2-d spectrum
(Data-Model)/Noise
b/g QSO z = 3.13
2-d spectrum
f/g QSO z = 2.29
background
QSO spectrum
Hennawi, Prochaska,
& Burles (2007)
Implied transverse
ionizing flux
gUV = 6370  UVB!
Near-IR Quasar Redshifts
Transverse Fluorescence?
PSF subtracted
2-d spectrum
(Data-Model)/Noise
Implied transverse
ionizing flux
gUV = 7870  UVB!
b/g QSO z = 2.35
2-d spectrum
f/g QSO z = 2.27
Background
QSO spectrum
Hennawi, Prochaska,
& Burles (2007)
metals at this z
Ly Emission from DLAs
Intervening DLAs
HST STIS Image
QSO
2-d Spectrum
zQSO
f Ly
L Ly
(10-17 erg s-1 cm-2)
(1042 erg s-1)
zDLA
PKS 0458-02
2.286
2.0395
5.4
0.17
PC0953+4749
4.457
3.407
0.7
0.77
Q 2206-1958
2.559
1.9205
26
14
DMS 2247-0209
4.36
4.097
0.5
0.9
Proximate DLAs
PHL 1222
1.922
1.9342
90
25
B 0405-331
2.57
2.570
???
???
PSK 0528-250
2.77
2.8115
7.4
0.49
SDSSJ 1240+1455
3.107
3.1078
43
39
Q2059-360
3.10
3.0830
20
18
Could the proximate DLA emission be
fluorescence excited by the quasar ionizing flux?
Moller et al. (2004)
Fluorescent Phases
Transverse
f/g QSO
R
b/g QSO
Absorber
Proximate
b/g QSO
Absorber
Full Moon?
Absorber
f/g QSO
A Fluorescing PDLA?
b/g QSO
R||
Hennawi, Kollmeier,
Prochaska, & Zheng
(2007)
DLA
• Ly brighter than 95% of LBGs --- unlikely to be star formation.
• Detection of N(N+4) > 1014.4 cm-2 consistent with hard QSO spectrum and
requires R|| < 700 kpc.
• Large fLy = 4.310-16 erg s-1 cm-2 suggests R|| ~ 300 kpc.
• If emission is Ly from QSO halo, then we can image DLA in silhouette.
New Probes of HI in High-z Galaxies
Statistics of PDLAs
Fluorescent Ly Emission
Ly Emissivity Map
Aperture Spectra
Photoevaporation
of DLAs
Column
distribution
near QSOs
Hennawi, Kollmeier, Prochaska, & Zheng (2007)
Hennawi, Prochaska,
& Herbert-Fort (2007)
• These observables are predictable given a model for HI distribution
in high-z galaxies.
• The physics of self-shielding and resonant line radiative transfer are
straightforward compared to other problems in galaxy formation.
Summary
• With projected QSO pairs, QSO environments can be studied down to ~ 20
kpc where ionizing fluxes are as large as 104 times the UVB.
• Clustering pattern of absorbers around QSOs is highly anisotropic.
• Rapid redshift evolution of QSO clustering compared to paucity of
proximate DLAs implies that photoevaporation has to be occuring.
• Physical arguments indicate that DLAs within 1 Mpc of a luminous quasar
can be photoevaporated.
• QSO-LLS pairs provide new laboratories to study Ly fluorescence.
• Null detections of fluorescence and clustering anisotropy suggest that quasar
emission is either anisotropic or variable on timescales < 105 yr.
• Photoevaporation and fluorescent emission provide new physical constraints
on the distribution of HI in high-z proto-galaxies. The input physics is
relatively simple and it can be easily modeled.