Quasars Probing Quasars: Shedding (Quasar) Light on High Redshift Galaxies Joseph F. Hennawi UC Berkeley Ohio State February 20, 2007

Suspects Xavier Prochaska (UCSC) Scott Burles (MIT) Juna Kollmeier (Carnegie) & Zheng Zheng (IAS)

Outline 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 L * (z)/L * (0) Dramatic evolution of number density / luminosity look back time Boyle et al. (2001) Richards et al. (2006) Tremaine et al. (2002) z (redshift)

Quasar Evolution for Pundits BLAGN Steffen et al. (2003) unidentified non-BLAGN The AGN unified model breaks down at high luminosities. “Almost all luminous quasars are unobscured... ” Barger et al. (2005) AGN unified model

10 6 M  3  10 5 M  10 5 M  Engargiola et al. (2002) HI in High Redshift Galaxies? Image credit: Fabian Walter Radial CO and HI profiles for 7 nearby galaxies (Wong & Blitz 2002). M33 HI/H  /Optical M33 HI/CO 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 –5000 deg 2 –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 deg 2 –500,000 z < 3 ; i < 21.0 –20,000 z > 3 ; i < 21.0 –Richards et al. 2004; Hennawi et al SDSS 2.5m ARC 3.5m Jim Gunn Follow up QSO pair confirmation from ARC 3.5m and MMT 6.5m MMT 6.5m

 = 3.7” 2’ 55” Excluded Area Finding Quasar Pairs SDSS z = low-z QSOs

Cosmology with Quasar Pairs Close Quasar Pair Survey 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  = 13.8”, z = 3.00; Beam =79 kpc/h Spectra from Keck ESI Keck Gemini-N Science 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 Gemini-S MMT Collaborators: Jason Prochaska, Crystal Martin, Sara Ellison, George Djorgovski, Scott Burles, Michael Strauss Ly  Forest Correlations CIV Metal Line Correlations Normalized Flux

IGM Primer

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

Self 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 M BH = 3  10 7 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 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

Fluorescent Ly  Emission In ionization equilibrium ~ 60% of recombinations yield a Ly  photon Since  1216 > 10 4  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 (2002)  912 ~ 1 in self shielding skin Shielded HI UV Background Only Ly  photons in tail can escape P(v) v dist of cloud

Imaging 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!

Help From a Nearby Quasar Adelberger et al. (2006) DLA trough 2-d Spectrum of Background Quasar Spatial Along Slit (”) Wavelength extended emission r = 15.7! Doubled Peaked Resonant Profile? Background QSO spectrum Transverse flux = 5700  UVB! f/g QSO R  = 384 kpc 11 kpc 4 kpc

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 < Since dN/dz(DLAs) = 0.2, then the probability P Chuck = 1/1000! I should spend less time at Keck, and more time in Vegas $$ Chuck Steidel Perhaps DLAs are strongly clustered around quasars?

Quasar-Absorber Clustering

Quasars Probing Quasars Hennawi, Prochaska, et al. (2007)

Transverse Clustering 29 new QSO-LLSs with R < 2 Mpc/h High covering factor for R < 100 kpc/h For  T (r) = (r/r T ) - ,  = 1.6, and N HI > cm -2, r T = 9  1.7 (2.9  QSO-LBG) Hennawi, Prochaska et al. (2007); Hennawi & Prochaska (2007) Chuck’s object = Keck = Gemini = SDSS = has absorber= no absorber Enhancement over UVB z (redshift)  = 2.0  = 1.6 QSO-LBG

Proximate DLAs: LOS clustering Found 12 PDLAs out of ~ 2000 z < 2.7 quasars Prochaska, Hennawi, & Herbert-Fort (2007) Transverse clustering strength at z = 2.5 predicts that nearly every QSO should have an absorber with N HI > 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 f/g QSO b/g QSO RR QSO is to DLA... as... O-star is to interstellar cloud Hennawi & Prochaska (2007) Otherwise it is photoevaporated Bertoldi (1989), Bertodi & McKee (1989) Cloud survives provided r = 17 r = 19 r = 21 n H = 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, P Chuck = 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: t cross ~ 4  10 5  = 20” (120 kpc/h). Current limit: t QSO > 10 4 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? background QSO spectrum 2-d spectrum f/g QSO z = 2.29 PSF subtracted 2-d spectrum (Data-Model)/Noise Hennawi, Prochaska, & Burles (2007) b/g QSO z = 3.13 Implied transverse ionizing flux g UV = 6370  UVB!

Near-IR Quasar Redshifts

Transverse Fluorescence? Background QSO spectrum 2-d spectrum f/g QSO z = 2.27 PSF subtracted 2-d spectrum (Data-Model)/Noise Hennawi, Prochaska, & Burles (2007) b/g QSO z = 2.35 Implied transverse ionizing flux g UV = 7870  UVB! metals at this z

Ly  Emission from DLAs Could the proximate DLA emission be fluorescence excited by the quasar ionizing flux? Moller et al. (2004) HST STIS Image 2-d Spectrum QSO z QSO z DLA f Ly  ( erg s -1 cm -2 ) L Ly  (10 42 erg s -1 ) PKS PC Q DMS PHL B ??? PSK SDSSJ Q Intervening DLAs Proximate DLAs

Fluorescent Phases Fluorescent Phases RR f/g QSO Transverse b/g QSO Absorber Full Moon? Absorber f/g QSO Absorber Proximate b/g QSO

A Fluorescing PDLA? Ly  brighter than 95% of LBGs --- unlikely to be star formation. Detection of N(N +4 ) > cm -2 consistent with hard QSO spectrum and requires R || < 700 kpc. Large f Ly  = 4.3  erg s -1 cm -2 suggests R || ~ 300 kpc. If emission is Ly  from QSO halo, then we can image DLA in silhouette. Hennawi, Kollmeier, Prochaska, & Zheng (2007) R || DLA b/g QSO

New Probes of HI in High-z Galaxies 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. Hennawi, Kollmeier, Prochaska, & Zheng (2007) Statistics of PDLAs Fluorescent Ly  Emission Photo- evaporation of DLAs Ly  Emissivity Map Aperture Spectra Hennawi, Prochaska, & Herbert-Fort (2007) Column distribution near QSOs

Summary With projected QSO pairs, QSO environments can be studied down to ~ 20 kpc where ionizing fluxes are as large as 10 4 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 < 10 5 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.