The Clowes-Campusano Large Quasar Group Survey

1. The Clowes-Campusano Large Quasar Group Survey R. Clowes (Univ. Lancashire, UK) I. Söchting (Oxford Univ., UK) K. Harris (Univ. Lancashire, UK) C. Haines (Univ. Birmingham, UK) J. Loveday (Univ. Sussex, UK) D. Valls-Gabaud (Obs. de Paris, F) M. Lehnert (Obs. De Paris, F) N. Nesvadba (Univ. Paris-Sud, F) G. Williger (UL, USA) L. Haberzettl (UL, USA) J.T. Lauroesch (UL, USA) M. Graham (Caltech, USA) R. Davé (Steward Obs., USA) A. Koekemoer (STScI, USA) L. Campusano (Univ. de Chile, CL)

2. The Clowes-Campusano LQG Survey Outline Background - Why important? - How to find them? - LQG "zoo" The CCLQG Survey Lyman Break Galaxies in the CCLQG Future

3. Why Large Quasar Groups Important • Quasars • -Signatures of physical mechanisms • - supermassive black holes+high accretion • - massive haloes • - feeding by gas-rich (major?) mergers? • - associated with high star formation • - Quenching in high density regions (gas stripping etc.) • - feedback mechanisms • - strong winds • - high ionization • Quasars thrive in somewhat overdense but not too overdense regions

4. Quasars: a stage of galaxy formation • duration of quasar phase << timescale for • quiescent evolution of AGN and age of Universe • LIFETIMES: ~10-30 (1-100?) Myr scales • at any time only small number of galaxies in • quasar phase

5. Large Quasar Groups:Efficient Sites of Quasar-Galaxy Relations • Galaxies bear signatures of merger rates •  give clue to recent merger activity in region • Galaxies give star formation histories •  clue to past merger/galaxy formation in region • Galaxies give measure of halo masses • Deep, wide galaxy surveys with lots of quasars  • efficient laboratories for studying physical mechanisms in both galaxy and quasar evolution

6. Background: LQGs • DISCOVERY: Webster 1982 →close triplet + one more distant QSO at z~0.37 scales ~75 h-1 Mpc • soon after: two other LQGs: Crampton et al. (87,89; 23 QSOs) at z~1.1 Clowes & Campusano (1991; 18 QSOs) z~1.3 • large irregular shaped, filamentary structures on scales of 50-200 Mpc with concentrations of5-20 QSO's • too large to be virialised, probable relics of large scale fluctuations • CURRENT VIEW: rare (4σ) structures,~1/3 space densityof galaxy super-clusters (Pilipenko 2007)

7. How to find Large Quasar Groups • Assumption: quasars randomly distributed • among galaxies with sufficient gas accretion • compare real QSO distributions to random • catalogues • usual spatial correlation functions not • efficient for finding filamentary structures • Alternatives: minimal spanning tree, • skeletons, spine of cosmic web

8. How to Find Structures Barrow et al. 1985 2Zwicky Galaxy Catalog 2Random Sample 1091 galaxies in the North Galactic Cap with Pmag ≤ 14 mag and δ≥0 and b≥40° 1091 galaxies over the same sky area

9. Minimal Spanning Tree (e.g. Barrow et al. 1985) • generalization of the nearest-neighbour or friend-of-friend method • connect points with unique path • distribution in tree length: • 1D: w1(l) = 1/l0 exp(-l/l0) • with <l> = l0 • 2D: w2(l) = 2l/l02 exp(-l2/l02) • with <l> = √(2π)/2 l0 • ⇩ • minimal tree if sum of length of segments is minimal • MST can be used to identify under- and over-dense regions

10. Minimal Spanning tree • define thresholds ltfor • maximum (over-dense) • minimum (under-dense) length of branches lt and • minimum number of objects in a domain M •  3D: density of clusters with l ≥ lt is higher than • threshold density if • ρt h<ρ><l3>/lt3 • (strongly depends on the choice of lt,M, determines • statistical significance)

11. Finding Structures in MST • two reduction methods to find structures • a) prune: strip branches of level k (≥3 connections) of dead-end connections • b) Prune + separate: also remove edges above a • cutoff length

12. The Clowes-Campusano LQG Survey MST pruned to level 10 (branches k≤ 10 removed) random mean edge length:<lz> = 0.0215 rad (1.232°) and <lr> = 0.0267 (1.530°)

13. MST: pruned and separated random cut-offs: 2<lz> and 1.6<lr> 0.043 rad (3.142˚) separation in both cases

14. MST length distributions random length length frequency distribution of MST(Zwicky) shows excess of large and small lzwicky frequency distribution of MST (random) follows Gauss distribution centered on <lrandom>

15. Pilipenko (2007) LQG survey • search in 2dF+SDSS QSO catalogs (> 100,000 QSOs) • 18 new LQG identified by MST + 2 LQG confirmed • contain 6 – 16 QSOs on scales ~40 – 155 h-1 Mpc • LQG TYPES: • "Regular": 14 LQGs • 6 – 8 members, scales ~60 h-1 Mpc, • spatial overdensity ≈ 10 • "Jumbo": 6 LQGs • 15 – 19 members, scales ~140 h-1 Mpc, • spatial overdensity ≈ 4 • space density: <n> ~ 7 h3Gpc3 ⇨~500 – 1000 Jumbo LQGs • morphologies: walls+blobs rather than filaments

16. Clowes-Campusano LQG • automated search on UKST objective-prism plate (~25.3 deg2) • ESO/SERC field 927 (1045+05 J2000) • 18 (up to 23+ depending on selection) quasars • with 1.2≤z≤1.4, Bj<20.4 (BRIGHT!) selection effect by objective-prism -- Ly-α emission shifted out of selection band at z>1.8 <z> = 1.27 • cover 2.5° x 5° on the sky • banana like structure

17. Subset of CCLQG (2.5x5 deg total, ~20 QSOs) CCLQG z~1.3 LQG z~0.8 3 x MgII-absorber overdensity 2 x MgII-absorber overdensity discovery of 2nd foreground LQG Williger et al. 2002

18. Clowes-Campusano LQG Survey • Galaxy populations in LQGs • Lyman Break Galaxies (LBGs) • red galaxy population • red sequence/blue cloud at z~1 in dense • environment (colour-density inversion • at z~1?) • Quasar-galaxy correlations/feedback • mechanism

19. Early Results 0.5º subfield: Red Galaxies Haines et al. 2004 CTIO BTC 4m V,I data ~0.25 deg2 subfield 31 x 27 h-2 Mpc2 at z ~ 1.2 2 x overdensity in red galaxies 3 x overdensity in red galaxies dashed contours 1.65 gal. arcmin-2

20. The Clowes-Campusano LQG Survey Existing Data Set: • 2 x 1.2˚ GALEX FUV+NUV • mlim~24.0 mag • SDSS u,g,r,i,z • ~1.6˚ Bok g mlim ~ 26 mag • 2 x 1˚CFHT r+z mlim ~ 26 mag • mlim ~ 24 mag • ~1.2˚KPNO 2.1m FLAMINGOS • NIR J+Ks • ~1° UKIRT Ks-band ~600 Magellan IMACS spectra 2 GALEX Medium Imaging Survey (used for WiggleZ bright LBGs)

21. The Clowes-Campusano LQG Survey Survey Summary

22. Efficient search for z~1 galaxies Lyman Break Galaxies (LBGs) search for LBGs at z~1 using FUV-dropout technique Lyman Break 912 Å at z~1 FUV-dropout examples: FUV NUV SDSS NUV FUV

23. Lyman Break Galaxies: Star-Formers • LBGs found over 0.5<z<7 • Common technique, signature of young stars • Z~4-5: lower mass systems, galaxies assembling • Z~3: progenitors of massive ellipticals • Z~2: use BzK technique (optical proxy), less massive systems (progenitors of grab-bag: S0, some massive spirals) • Z~ 1: One field studied (Burgarella et al.)

24. The Clowes-Campusano LQG Survey LBG search + selection criteria GALEX NUV selected sample: ~15,800 objects SDSS DR5 cross-correlation: ~13,800 primary counterparts LBG selection criteria - Burgarella et al. (2006): mNUV≤ 24.5 mag + FUV – NUV ≥ 2 additional selection criteria: resolved by Sloan Survey (SDSS) - extended source = galaxy resulting sample ~1000 LBG candidates

25. The Clowes-Campusano LQG Survey photometric redshift distribution LBG candidates dz = 0.05-0.10 LQG@z~0.8 CCLQG@z~1.3

26. The Clowes-Campusano LQG Survey selecting redshift+luminosity limited subsample 2 redshift bins in front of the LQGs LQG@z~0.8 CCLQG@z~1.3 bright: MNUV≤ M*NUV faint: MNUV> M*NUV Arnouts et al. (2005)

27. LBGs: old population component SFHs of stacked/averaged LBG SEDs χ2-fit of averaged and normalized LBG SEDs to library of PÉGASE models LQG@z~0.8 3 Gyr ≤ tbest≤ 7 Gyr although fits with 250 ≤ tyoungest ≤ 800 are acceptable CCLQG@z~1.3 3 Gyr ≤ tbest≤ 7 Gyr

28. The Clowes-Campusano LQG Survey ~500 Myr results for best fitting ages show significant older tbest than Burgarella et al. 2007 (250≤tbest≤500 Myr) Burgarella sample include fainter LBGs  younger star bursts  younger averaged SEDs? Our survey shallower, biased toward higher mass LBGs? ~250 Myr

29. Results Affected by Confusion? • GALEX point spread function ~5-6 arcsec • Depth of NUV~23.5-24 begins to be affected by confusion • Compare with deep, 1 arcsec resolution CFHT r-band images • ~20% of LBGs have >1 r-selected counterpart • Confusion effect is small compared to scatter (factor of few to 10-100) in stacked spectral energy distributions

30. QSOs on LBG Cluster Outskirts? LBG concentrations + filaments LBGs in proximity to QSOs  QSO feedback mechanism?

31. z~0.8 Quasar-LBG correlations P=0.0027 1'~0.5 local Mpc P=0.0051,0.0056 117 LBGs, 17 quasars, 10000 random quasar placements

32. QSOs on (red) cluster outskirts? Need better photometric redshifts (near-IR) to bin in redshift red galaxies tend to avoid QSOs formation of large filaments

33. Summary/Conclusions Large quasar groups ~ quasar superclusters, useful laboratories for studying quasar-galaxy relations in large structure contexts Clowes-Campusano LQG field being explored in 2 deg2 multi-wavelength survey z~1 LBGs several Gyr old, older than only other study – due to shallower survey, more massive LBGs? LBG-quasar correlation suggested to eye but does not show robust statistical signal (yet?) – need more data

34. The Clowes-Campusano LQG Survey • future: • - Bok+90prime observations • g in southern field • medium band imaging (N,S) • (done Mar 2008) • - AAT spectra • - CFHT queue observation r+z • extend existing field ~5 deg2 • - GALEX PI team Medium Deep Survey Extension: 6 fields • - Science: individual galaxy SEDs, color-density relation, AGN, … • - Study LQG analogues in Millennium Simulation • - Mark Younger discovered 3 z~2 LQGs – theory v. data Future Plans