Quasars Probing QuasarsQuasars Probing Quasars

Joseph F. HennawiBerkeley

Hubble SymposiumApril 20, 2006

z = 2.53

z = 2.44

f/g QSO

b/g QSO

R

Suspects

Michael Strauss(Princeton)

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Jason Prochaska(UCSC)

Scott Burles(MIT)

OutlineOutline

• Primer on quasar absorption lines

• Proximity effects

• Fluorescent Ly Emission

• Anisotropic clustering of absorbers around

quasars

• Shedding light on DLAs

Quasar Absorption LinesQuasar Absorption Lines

DLA (HST/STIS)

Moller et al. (2003)

LLS

Nobody et al. (200?)

Lyz = 2.96

Lyman Limitz = 2.96

QSO z = 3.0 LLS

Lyz = 2.58

DLA

• 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

• Damped Ly Systems (DLAs)– NHI > 1020.3 comparable to disks

– sub-L galaxies?

– Dominate HI content of Universe

Self Shielding: A Local ExampleSelf Shielding: A Local Example

Sharp edges of galaxy disks set by ionization equilibrium with the UV background. HI is ‘self-shielded’ from extragalactic UV photons.

Braun & Thilker (2004)M31 (Andromeda) M33 VLA 21cm map

DLA

Ly forest

LLS

What if the MBH = 3107 M black hole at Andromeda’s center started accreting at the Eddington limit? What would M33 look like then?

bump due

to M33

Average HI of Andromeda

Neutral Gas

Isolated QSO

Proximity EffectsProximity Effects

• 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?

Ionized Gas

Projected QSO Pair

Cosmology with Quasar PairsCosmology with Quasar PairsClose Quasar Pair Survey

• Discovered ~ 100 sub-Mpc pairs (z > 2)

• Factor 20 increase in number known

• ~ 30 systems with beam < 100 kpc/h

= 5.4”, z = 2.05; Beam =86-99 kpc/h

Spectrum from Keck LRIS-B

Keck Gemini-N MMT

Gemini N-S

Science Goals• Small scale structure of Ly forest

• Transverse proximity effects

• Constrain dark energy from AP test

• Moderate Resolution Spectra

• Near-IR Foreground QSO Redshifts

Fluorescent EmissionFluorescent Emission

• 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

Zheng & Miralda-Escude (2005)

912 ~ 1 in self shielding skin

Shielded HI

UV Background

x =δυ /υσ / c

= 0e−(x2 /2)

Only Ly photons in tail can escape

P(v)

v dist of cloud

Imaging Optically Thick AbsorbersImaging Optically Thick Absorbers

Cantalupo et al. (2005)

Column Density Ly Surface Brightness

• Expected surface brightness:

• Still not detected. Even after 60h integrations on 10m telescopes!

or

Sounds pretty hard!

SBLy =3.7 ×10−20 J −22

912

4⎛

⎝⎜⎞

⎠⎟1+ z4

⎛⎝⎜

⎞⎠⎟

−4

egσ cm -2σ-1W" mLyα = 30 mag/W"

Help From a Nearby QuasarHelp From a Nearby Quasar

Adelberger et al. (2006)

DLAtrough

2-d Spectrum of Background Quasar

Spatial Along Slit (”)W

avel

engt

h

extended emission

r = 15.7!

Doubled Peaked Resonant Profile?

Background QSO spectrum

5700 UV background!

Why Did Chuck Get So Lucky?Why Did Chuck Get So Lucky?

f/g QSO

R||

b/g QSO

R = 280 kpc/h

DLA must be in this

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.

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!

Perhaps DLAs are strongly clustered around quasars?

I should spend less time at Keck, and more time in Vegas $$

Chuck Steidel

Absorbers Near QuasarsAbsorbers Near Quasars

z = 2.53

z = 2.44

z = 2.17 z = 2.07

z = 1.98z = 2.11

= 16”, R= 97 kpc/h, gUV = 365 = 23”, R= 139 kpc/h, gUV = 420

LLS: NHI = 1019 cm-2

Hennawi, Prochaska, et al. (2006)

DLA: NHI = 1020.3 cm-2LLS: NHI = 1019.7 cm-2

= 13”, R= 78 kpc/h, gUV = 630

Absorption probability for LOS as predicted by transverse clustering

DLAs from

Russell et al. (2006)

No clustering

Anisotropic ClusteringAnisotropic Clustering

• 29 new QSO-LLSs with R < 2 Mpc/h

• High covering factor for R < 100 kpc/h

• Assuming T(r) = (r/rT)-g and g = 1.6, rT

= 9 1.7 (2.9 QSO-LBG)

Transverse clustering predicts every QSO

should have an absorber along the LOS

Hennawi, Prochaska et al. (2006); Hennawi & Prochaska (2006a)

Chuck’s object

= Keck = Gemini = SDSS

= has absorber = no absorber

En

han

cem

ent

over

UV

Bz

(re

dsh

ift)

Proximity Effects: Open QuestionsProximity 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?

Shedding Light on DLAsShedding Light on DLAs

f/g QSO

b/g QSO

R = 280 kpc/h

gUV = 5700

QSO is to DLA . . . as . . . O-star is to interstellar cloud

‘Typical’ numbers for DLA: Γ =nphotons

nH

= 3 ×10−3 S56

RMpc2

nH

10-2

⎛⎝⎜

⎞⎠⎟

−1

= 2.2

δ =500nH

10−2

⎛⎝⎜

⎞⎠⎟

−1NHI = 1020.3 cm-2 and r ~ 5 kpc

nH ~ 0.01 cm-3

Hennawi & Prochaska (2006a)

ionization parameter

Survival requires nH > 9 cm-3 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?

δ =0.29Γ

10−3

⎛⎝⎜

⎞⎠⎟

NHI

1020.3cm-2

⎛⎝⎜

⎞⎠⎟

−1

< 1

Otherwise it is photoevaporatedBertoldi (1989), Bertoldi & Mckee (1989)

Cloud survives provided

Got Fluorescence?Got Fluorescence?

= 6.2”, R= 37 kpc/h

LLS: NHI = 1018.85 cm-23.5 hour integration on Gemini

mLyα ~ 19.5 mag/W"

• gUV = 7900 UVB

expect

(Chuck’s gUV = 5700)

• Two other similar systems show no fluorescence

• ‘Odd’ HI profiles? Unresolved emission?

background QSO spectrum

2-d spectrum

b/g QSO

f/g QSO

PSF subtracted 2-d spectrum

Hennawi & Prochaska (2006b)

Summary: Quasars Probing QuasarsSummary: 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.

mLyα : 19.5 mag/W"

dN

dz=

dNdz

1+ c(R⊥ ,z)[ ]

Quantifying Absorber Clustering Quantifying Absorber Clustering

• 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.

Far from a QSO

R

Transverse Line of Sight

isolated QSO

dN

dz=nA

dDdz

dN

dz=

dNdz

1+ c(v)[ ]

f/g QSO

Cosmic Average

z r c =1

Vξ (r)dV∫

b/g QSO

z z

cutoff

Close Pairs and the LyClose Pairs and the Ly Forest Forest

Neutral Gas

FWHM

Perfect20 km/s40 km/s80 km/s

160 km/s

1 pair at S/N=20Ability of single pair to distinguish WDE = 0.7 from WDE = 0.8 (courtesy of Pat McDonald)

Goal: Measure transverse Ly correlations of close pairs with z > 2

quasar

– Probe WDE at z ~ 2 with the Alcock - Paczynski test

pair

– Measure ‘Jeans Mass’ of Ly clouds

thermal history of IGM

Science:– Extend power spectrum measurements to small scales

Small Scale Power at z = 2Small Scale Power at z = 2 = 5.4” z = 2.05, 2.09 Beam =86-99 kpc/h (comoving)

Small Scale Power at z = 3Small Scale Power at z = 3 = 13.8” z = 3.0 Beam =274-306 kpc/h (comoving)

Common Absorbers

Tomography with Quasar GroupsTomography with Quasar Groups

8’

5’

z = 2.08 z = 1.8

z = 2.17 z = 2.39

z = 2.6

Keck LRIS mask