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Quasars Probing Quasars: Shedding (Quasar) Light on High Redshift Galaxies

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

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Quasars Probing Quasars: Shedding (Quasar) Light on High Redshift Galaxies

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

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

  3. 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.

  4. Motivation

  5. A Simple Observation Spectrum from Wallace Sargent

  6. Quasars Evolution for Poets Progenitors Relics Richards et al. (2006) Tremaine et al. (2002) Comoving Number Density z (redshift) Dramatic evolution of number density/ luminosity Boyle et al. (2001) L*(z)/L*(0) look back time

  7. 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 . . . ”

  8. 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).

  9. The Power of Large Surveys Apache Point Observatory (APO) ARC 3.5m Jim Gunn • Spectroscopic QSO survey • 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 SDSS 2.5m MMT 6.5m Follow up QSO pair confirmation from ARC 3.5m and MMT 6.5m

  10.  = 3.7” 55” Excluded Area Finding Quasar Pairs low-z QSOs 2’ 2.0 2.0 3.0 4.0 3.0 SDSS quasar @ z =3.13 2.0 4.0 3.0

  11. 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 Ly Forest Correlations Normalized Flux CIV Metal Line Correlations Keck MMT Gemini-S 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  = 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

  12. IGM Primer

  13. Lyman Limit z = 2.96 Ly z = 2.96 Ly z = 2.58 LLS DLA (HST/STIS) DLA LLS ? Moller et al. (2003) Nobody et al. (200?) 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 • Damped Ly Systems (DLAs) • NHI > 1020.3 comparable to disks • sub-L galaxies? • Dominate HI content of Universe QSO z = 3.0

  14. Self Shielding: A Local Example Average HI of Andromeda bump due to M33 LLS Ly forest M33 VLA 21cm map M31 (Andromeda) 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?

  15. Ionized Gas Proximity Effects Isolated QSO Projected QSO Pair Neutral 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?

  16. Fluorescent Ly 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 (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

  17. 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!

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

  19. I should spend less time at Keck, and more time in Vegas $$ Chuck Steidel 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! Perhaps DLAs are strongly clustered around quasars?

  20. Quasar-Absorber Clustering

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

  22. Transverse Clustering Hennawi, Prochaska et al. (2007); Hennawi & Prochaska (2007) Enhancement over UVB Chuck’s object • 29 new QSO-LLSs with R < 2 Mpc/h • 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)  = 2.0  = 1.6 QSO-LBG z (redshift) = SDSS = Keck = Gemini = has absorber = no absorber

  23. Proximate DLAs: LOS clustering Prochaska, Hennawi, & Herbert-Fort (2007) • Found 12 PDLAs out of ~ 2000 z < 2.7 quasars • 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.

  24. Photoevaporation QSO is to DLA . . . as . . . O-star is to interstellar cloud Cloud survives provided b/g QSO f/g QSO R Otherwise it is photoevaporated Bertoldi (1989), Bertodi & McKee (1989) r = 17 r = 19 r = 21 nH = 0.1 Hennawi & Prochaska (2007)

  25. 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

  26. 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?

  27. Fluorescent Ly Emission

  28. Transverse Fluorescence? PSF subtracted 2-d spectrum (Data-Model)/Noise Implied transverse ionizing flux gUV = 6370  UVB! b/g QSO z = 3.13 2-d spectrum f/g QSO z = 2.29 background QSO spectrum Hennawi, Prochaska, & Burles (2007)

  29. Near-IR Quasar Redshifts

  30. 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 metals at this z Background QSO spectrum Hennawi, Prochaska, & Burles (2007)

  31. Ly Emission from DLAs Intervening DLAs HST STIS Image 2-d Spectrum Proximate DLAs Could the proximate DLA emission be fluorescence excited by the quasar ionizing flux? Moller et al. (2004)

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

  33. A Fluorescing PDLA? b/g QSO R|| DLA Hennawi, Kollmeier, Prochaska, & Zheng (2007) • 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.

  34. New Probes of HI in High-z Galaxies Fluorescent Ly Emission Statistics of PDLAs Ly Emissivity Map Aperture Spectra Photo-evaporation 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.

  35. 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.

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