Binary Quasars in the Sloan Digital Sky Survey Joseph F. Hennawi Berkeley Hubble Symposium April 7, 2005

Suspects Naohisa Inada (Tokyo) Masamune Oguri (Princeton) Michael Strauss (Princeton) Gordon Richards (Princeton)

Conclusions New sample of 26 binary quasars with separations R < 50 kpc/h more than doubles the number known First measurement of quasar clustering on small scales 10 kpc/h < R < 400 kpc/h (proper) The quasar correlation function gets progressively steeper on sub-Mpc scales Factor of excess clustering is detected on scales < 40 kpc/h over extrapolation of large scale power law Is excess clustering the hallmark of mergers and dissipative interactions which trigger quasar activity in rich environments?

An Old Problem: Excess Close Pairs Djorgovski (1991) Djorgovski realized that 3 close pairs in sample ~ 3000, implies a pair probability P(R< 200 kpc/h) ~ Binary Quasar Lore –tides/mergers galaxy activated –large R ~ 100 kpc/h no tides –small R ~ 10 kpc/h t DF < t H P(<R) Probability of Having a Companion R [kpc/h] Comoving Transverse Separation Could these be strong lenses? –No corresponding radio population –Requires dark/exotic mass concentration –“We don’t expect splittings this large....”

Small Scale Quasar Clustering Fiber Collisions: Optical fibers can only be packed so tightly –For 2dF: No pairs with  < 35” –For SDSS: No pairs with  < 55” Shot Noise –Volume decreases faster than the correlation function increases Proper Mpc/h Comoving Mpc/h Solutions 1. Wait for next generation all sky (i < 21) spectroscopic survey of ~ 10 6 quasars –Several years of observing –Need $$ + huge consortium of people n = 35 deg Target only ~ 200 close pairs (i < 21) –Use LF to get mean density –Less than 20 nights of observing –Sucker in one graduate student 2dF: Croom et al. (2005)

Why Observe at Princeton? Apache Point Observatory (APO) SDSS spectroscopic survey –4000 deg 2 –45,000 low -z quasars i < 19.1 –5,000 z > 3 quasars i < 20.2 –Precise 5 band (u,g,r, i, z) photometry SDSS 2.5m ARC 3.5m ARC 3.5m telescope –Plenty of time available in a department full of theorists –Remote operation from comfort of basement of Peyton Hall –There was little else to do at night in Princeton Jim Gunn

low-z qsos A-stars UVX WD 2’ 55” Excluded Area Finding Quasar Pairs  = 14.7” Keck Spectrum taken by Bob Becker & Michael Gregg SDSS z =2.17

Binary Quasars in the SDSS Statistical Clustering Sample –Subset of full sample with quantifiable selection criteria –38 binaries below fiber collision limit (  < 55”; R< 400 kpc/h) Full Binary Sample Statistical Clustering Sample Pairs found from SDSS Sparse sampling of this region Dense sampling of this region Fiber collision (  = 55”) Barely Resolved (  = 3”) Full Binary Sample –26 new binaries with R < 50 kpc/h (  < 10”) –More than doubles the number of such systems known!

Excess Small Scale Clustering Factor ~ 10 excess for R < 40 kpc/h. Rises to ~ 30 for R ~ 10 kpc/h Quasar correlation function progressively steepens for R < 1 Mpc/h Is excess clustering the hallmark of mergers and dissipative interactions? High redshift galaxies (z = 1- 3) show no excess clustering, but measurements don’t yet probe R < 100 kpc/h Hennawi et al. (2005) Projected Correlation Function Extrapolation of larger scale 2dF clustering Ratio of Observed/Extrapolated Uncertain selection function for smallest angles Fiber Collision

Future Directions Use photometric selection to measure clustering with better statistics Push to high redshift binary quasars at z > 4 Deep imaging to study the environments of these systems. Proto-clusters at z ~ 2? Measure transverse small scale Ly  forest correlations with quasar pairs with z > 2

Excess Galaxy Clustering? Low-z galaxies lie on a single power law down to 10 kpc/h (comoving) High redshift (DEEP2, LBGs) clustering does not probe < 100 kpc/h Quasar-Galaxy correlations do not yet probe relevant scales or redshifts SDSS Galaxies z ~ 0.1 Coil et al. (2004) DEEP2 Galaxies z = Masjedi et al. in prep LBGs at z ~ 3 Adelberger (2003)

A B C D G1 Inada et al. (2003) Oguri et al. (2004) Inada et al. (2005) z=1.734 The Widest Lensed Quasar Largest Splitting  = 14.6”! HST ACS HST NICMOS SDSS spectroscopic survey –4000 deg 2 –45,000 low -z quasars i < 19.1 –5,000 z > 3 quasars i < 20.2 –Precise 5 band (u,g,r, i, z) photometry

SDSS Spectroscopic Quasars SDSS Photometric Quasars Predict ~ 2 lenses with  > 10” in current (~ 4000 deg 2 ) sample Consistent with discovery of quad lens SDSS How Many Quasars Lensed by Clusters? Predict ~ 8 lenses with  > 10” in current (~ 7000 deg 2 ) sample ~ 1 should have  > 30” ~ 1 will have z s ~ 4 Hennawi, Dalal, & Bode (2005) From Ray Tracing Simulations through LCDM clusters