1. Quasars Probing Quasars
z = 2.53
b/g QSO
z = 2.44 R
f/g QSO
Quasars Probing Quasars
Joseph F. Hennawi
Berkeley
Hubble Symposium
April 20, 2006

2. Suspects Michael Strauss Scott Burles Jason Prochaska (Princeton)
(UCSC)
Michael Strauss
(Princeton)
Scott Burles
(MIT)

3. Outline Primer on quasar absorption lines Proximity effects
Fluorescent Ly Emission
Anisotropic clustering of absorbers around quasars
Shedding light on DLAs

4. Quasar Absorption Lines
Ly Forest
Optically thin diffuse IGM
/ ~ 1-10; 1014 < NHI <
well studied for R > 1 Mpc/h
Lyman Limit Systems (LLSs)
Optically thick 912 > 1
< NHI <
almost totally unexplored
Damped Ly Systems (DLAs)
NHI > comparable to disks
sub-L galaxies?
Dominate HI content of Universe
Ly
z = 2.96
Lyman Limit
Ly
z = 2.58
QSO
z = 3.0
DLA
LLS
DLA (HST/STIS)
Moller et al. (2003)
LLS
Nobody et al. (200?) ?

5. Self Shielding: A Local Example
Average HI of Andromeda
bump due
to M33
LLS
Ly
forest
M31 (Andromeda)
M33 VLA 21cm map
Braun & Thilker (2004)
DLA
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?

6. Proximity Effects
Projected QSO Pair
Isolated QSO
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?)
Quasar lifetime/variability
Measure distribution of HI in quasar environments
Are there similar effects for optically thick absorbers?

7. Cosmology with Quasar Pairs
 = 5.4”, z = 2.05; Beam =86-99 kpc/h
Close Quasar Pair Survey
Discovered ~ 100 sub-Mpc pairs (z > 2)
Factor 20 increase in number known
~ 30 systems with beam < 100 kpc/h
Moderate Resolution Spectra
Keck
Gemini-N
MMT
Near-IR Foreground QSO Redshifts
Gemini N-S
Science Goals
Small scale structure of Ly forest
Transverse proximity effects
Constrain dark energy from AP test
Spectrum from Keck LRIS-B

8. Fluorescent Emission
Shielded HI
912 ~ 1 in self
shielding skin
UV Background
v dist of cloud
P(v)
Only Ly photons in tail can escape
Zheng & Miralda-Escude (2005)
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

9. Imaging Optically Thick Absorbers
Column Density
Ly Surface Brightness
Cantalupo et al. (2005)
Expected surface brightness:
Still not detected. Even after 60h integrations on 10m telescopes! or
Sounds pretty hard!

10. Help From a Nearby Quasar
Background QSO spectrum
2-d Spectrum of Background Quasar
5700  UV background!
Wavelength
r = 15.7!
DLA
trough
extended emission
Spatial Along Slit (”)
Adelberger et al. (2006)
Doubled Peaked Resonant Profile?

11. Why Did Chuck Get So Lucky?
b/g QSO
Surface brightness consistent with expectation for R|| = 0
R|| constrained to be very small, otherwise fluorescence would be way too dim.
DLA must be in this region to see emission
f/g QSO
R||
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 $$
Chuck Steidel
Perhaps DLAs are strongly clustered around quasars?

12. Absorbers Near Quasars
 = 13”, R= 78 kpc/h, gUV = 630
 = 16”, R= 97 kpc/h, gUV = 365
 = 23”, R= 139 kpc/h, gUV = 420
z = 2.17
z = 2.53
z = 2.07
z = 1.98
z = 2.11
z = 2.44
LLS: NHI = cm-2
LLS: NHI = cm-2
DLA: NHI = cm-2
Hennawi, Prochaska, et al. (2006)

13. Anisotropic Clustering
Hennawi, Prochaska et al. (2006); Hennawi & Prochaska (2006a)
29 new QSO-LLSs with R < 2 Mpc/h
High covering factor for R < 100 kpc/h
Assuming T(r) = (r/rT)- and  = 1.6, rT = 9  (2.9  QSO-LBG)
Enhancement over UVB
Chuck’s object
Absorption probability for LOS as predicted by transverse clustering
DLAs from
Russell et al. (2006)
No clustering
z (redshift)
= Keck
= Gemini
= SDSS
Transverse clustering predicts every QSO should have an absorber along the LOS
= has absorber
= no absorber

14. Proximity Effects: Open Questions
There is a LOS proximity effect but not a transverse one.
Measured T(r) gives, PChuck = 1/60.
Fluorescent emission proves Chuck’s DLA was illuminated.
Clustering anisotropy suggests most systems may not be.
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 at  = 20” (120 kpc/h). Current best limit: tQSO > 104
Can we measure the average opening angle?
Yes, but it requires a model for absorbers and QSO-HI clustering.
Much easier for optically thin transverse effect (coming soon).
Does high covering factor conflict with obscured fractions (~ 30%) of luminous QSOs?
Where are the metals from evaporated DLAs/LLSs near QSOs?

15. Hennawi & Prochaska (2006a)
Shedding Light on DLAs
QSO is to DLA as O-star is to interstellar cloud
Otherwise it is photoevaporated
Bertoldi (1989), Bertoldi & Mckee (1989)
Cloud survives provided
gUV = 5700
b/g QSO
f/g QSO
R = 280 kpc/h
‘Typical’ numbers for DLA:
NHI = cm-2 and r ~ 5 kpc
nH ~ 0.01 cm-3
Hennawi & Prochaska (2006a)
ionization parameter
Survival requires nH > 9 cm r < 11 pc. But Chuck’s fluorescence was resolved in 0.5” seeing r ~ 4 kpc? Two phase medium? Is a disk shielding the galactic halo?

16. Hennawi & Prochaska (2006b)
Got Fluorescence?
Hennawi & Prochaska (2006b)
gUV = 7900  UVB expect
(Chuck’s gUV = 5700)
Two other similar systems show no fluorescence
‘Odd’ HI profiles? Unresolved emission?
PSF subtracted 2-d spectrum
b/g QSO
2-d spectrum
f/g QSO
 = 6.2”, R= 37 kpc/h
background QSO spectrum
3.5 hour integration on Gemini
LLS: NHI = cm-2

17. Summary: Quasars Probing Quasars
QSO-absorber pairs probe anisotropy of luminous QSO emission at z > 2.
With fluorescents emission, LLSs act as mirrors giving us another view of high redshift QSOs.
New measure of the clustering of faint galaxies around quasars.
New laboratories to study fluorescent emission. LLSs illuminated by quasars are as bright as
Detection of fluorescence constrains quasar lifetime, tQSO > tcross , for individual QSOs!
New opportunities to study the distribution of HI in high-z proto-galaxies subject to extreme UV radiation.

18. Quantifying Absorber Clustering
Cosmic Average
Transverse
Line of Sight
b/g QSO
isolated QSO
cutoff
f/g QSO z
Far from a QSO z z r R
dN/dz only constrains product of number density and cross section.
Size does not matter for transverse. It does matter for line of sight.
Only rare close pairs probe small scales for transverse.
Every isolated line of sight probes small scales.

19. Close Pairs and the Ly Forest
quasar
Neutral Gas
Goal: Measure transverse Ly correlations of close pairs with z > 2
Science:
Extend power spectrum measurements to small scales
FWHM
Perfect
20 km/s
40 km/s
80 km/s
160 km/s
1 pair at S/N=20
Ability of single pair to distinguish
DE = 0.7 from DE = 0.8
(courtesy of Pat McDonald)
Measure ‘Jeans Mass’ of Ly clouds
thermal history of IGM
Probe DE at z ~ 2 with the Alcock - Paczynski test

20. Small Scale Power at z = 2
 = 5.4” z = 2.05, Beam =86-99 kpc/h (comoving)

21. Small Scale Power at z = 3
 = 13.8” z = 3.0 Beam = kpc/h (comoving)
Common Absorbers

22. Tomography with Quasar Groups
z = 1.8
z = 2.08
z = 2.17
z = 2.39 8’
z = 2.6
Keck LRIS mask 5’