Quasars Probing Quasars
Joseph F. Hennawi
UC Berkeley
&
OSU
October 3, 2007
Xavier Prochaska
(UCSC)
A Simple Observation
Spectrum from Wallace Sargent
The Basic Picture
Transverse
Line-of-Sight
b/g QSO
QSO
R
HI cloud
R||
f/g QSO
HI cloud
• Ly absorption can probe 8 decades in NHI (Ly is large!).
• Neighboring sightline provides a another view of the QSO.
• Redshift space distortions from kT motions (~ 20 km/s )
smooth with Gaussian of Rprop ~ 60 kpc = 10” @ z = 2.
• Need projected QSO pairs to study small scales!
What Can Proximity Effects
Teach Us?
nQSO ( L)
•
•
•
•
•
tQSO   
nHost/Relics ( ?) ;


t H  4 
nQSO


4 nQSO  nobscured
How is HI distributed around quasars?
What is the quasar duty cycle tQSO/tH ?
What is the obscured fraction (1- Ω/4)?
Can we constrain episodic QSO variability, tburst?
Directly observe impact of AGN feedback on the
IGM?
Physics of IGM well understood
no sub-grid physics or semi-analytical recipes!
Mining Large Surveys
Apache Point Observatory (APO)
• Spectroscopic QSO survey
–
–
–
–
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 QSO @ z =3.13
b/g QSO z = 3.13
2.0
4.0
3.0
f/g QSO z = 2.29
Keck LRIS spectra
 (Å)
Cosmology with Quasar Pairs
Close Quasar Pair Survey
Normalized Flux
Ly Forest Correlations
•
•
•
•
•
Discovered > 100 sub-Mpc pairs (z > 2)
Factor 25 increase in number known
Moderate & Echelle Resolution Spectra
Near-IR Foreground QSO Redshifts
About 50 Keck & Gemni nights.
CIV Metal Line Correlations
Keck
Gemini-N
Gemini-S
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
•
•
•
•
•
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
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?
Transverse Optically Thick
zbg = 3.13; zfg= 2.29; R = 22 kpc/h; logNHI = 20.5
zbg = 2.53; zfg= 2.43; R = 78 kpc/h; logNHI = 19.7
zbg = 2.07; zfg= 1.98; R = 139 kpc/h; logNHI = 19.0
zbg = 2.17; zfg= 2.11; R = 97 kpc/h; logNHI = 20.3
zbg = 2.21; zfg= 2.18; R = 61 kpc/h; logNHI = 18.5
zbg = 2.35; zfg= 2.28; R = 37 kpc/h; logNHI = 18.9
Hennawi, Prochaska, et al. (2007)
Transverse Optically Thick
Clustering
Hennawi, Prochaska et al. (2007);
Hennawi & Prochaska (2007)
Enhancement over UVB
• 29 new QSO-LLSs with R < 2 Mpc/h
• High covering factor for R < 100 kpc/h
• For T(r) = (r/rT)-,  = 1.6, log NHI > 19
rT = 9  1.7 Mpc/h (3  QSO-LBG)
z (redshift)
 = 2.0
 = 1.6
QSO-LBG
= Keck
= Gemini
= has absorber
= SDSS
= no absorber
Line-of-Sight Clustering
Proximate DLA  DLA within v < 3000 km/s
Line-of-Sight Clustering Strength
1 + ||(∆v)
Transverse prediction
Extrapolation of trans. predictions
Line-of-sight measurements
z
Prochaska, Hennawi, & Herbert-Fort (2007)
• Factor 5-10 fewer PDLAs then expected from transverse clustering.
• Transverse clustering strength at z = 2.5 predicts that ~ 90% of QSO’s
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
t
N


  rec  500  20.3 H -2   1
 10 cm 
t IF
nphotons
-2

 2.6  10 4 S56 RMpc
n 1H, -1
nH
Otherwise it is photoevaporated
Bertoldi (1989), Bertodi & McKee (1989)
log NHI = 20.3
r = 17
r = 19
r = 21
Hennawi & Prochaska (2007a)
nH = 0.1
Emission Anisotropy
Obscuration/Beaming
Episodic Variability
b/g QSO
f/g QSO

R
b/g QSO
f/g QSO
R
Ionization state of
gas depends on QSO
at time t = t0 - R/c
Absorber
Absorber
>
104
yr
t = t0
We observe light emitted
at time t = t0
• Episodic Variability  QSO’s vary significantly on timescale
t < tcross ~ 4 105 yr @  = 20” (120 kpc/h).
Current best limit is tburst > 104 yr.
Proximity Effects: Thick and Thin
• Optically Thick LLSs and DLAs (today’s talk)
– Nature of absorbers near QSO’s is unclear.
• Gas entrained from AGN driven outflow? (AGN feedback!)
• Absorption from nearby dwarf galaxies?
– To measure tQSO/tH  or (Ω/4) we need to model
absorbers and do radiative transfer (hard).
• Optically Thin Ly Forest (in progess)
– Best for constraining tQSO/tH  and (Ω/4).
– Why? Because we can predict the Ly forest
fluctuations ab initio from N-body simulations (easy).
Optically Thin (Sneak Preview)
Hennawi, et al. (2007), in prep
Enhancement over UVB
Gemini NIRI K-band spectrum
 (m)
z (redshift)
z = 2.4360
z = 44 km/s
gUV  1 
FQSO
FUVB
    Ly g UV
;  Ly
Sample
• 1.6 < z < 4.5; 20 kpc < R < 10 Mpc
,
,
= Keck
= accurate z
= Gemini
,
= SDSS
= no accurate z
• 59 pairs with gUV > 100.
• 30 accurate near-IR redshifts.
Transverse Proximity Effect?
Spectrum from Keck ESI
Gemini NIRI K-band spectrum
Real
z = 3.8135
z = 44 km/s
Simulated
with f/g QSO
zbg = 4.11, zfg= 3.81
 = 34”, R = 175 kpc/h
without f/g QSO
Hennawi et al. 2007, in prep.
tcross = 5.7107 yr
gUV = 626!
Summary
• With projected pairs, QSO environments can be probed
down to ~ 20 kpc where ionizing flux is ~ 104 times the UVB.
• Clustering of optically thick absorbers around QSOs is
highly anisotropic.
• Paucity of PDLAs implies photoevaporation has to occur.
• Physical arguments indicate DLAs < 1 Mpc from a QSO can
be photoevaporated.
• There is a LOS optically thick proximity effect but no
transverse one.
• Either QSOs emit anisotropically or are variable on
timescales < 106 yr.
• The optically thin proximity effect will distinguish between
these two possibility and yield new quantitative constraints.