The Clowes-Campusano Large Quasar Group Survey

The Clowes-Campusano Large Quasar Group Survey

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)

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)

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

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 ionizationQuasars thrive in somewhat overdense but not too overdense regions

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

Quasars: a stage of galaxy formation

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

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 of 5-20 QSO's

too large to be virialised, probable relics of large scale fluctuations

CURRENT VIEW: rare (4σ) structures, ~1/3 space density of galaxy super-clusters (Pilipenko 2007)

Background: LQGs

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

How to find Large Quasar Groups

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

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/l

0 exp(-l/l

0)

with <l> = l0

2D: w2(l) = 2l/l

02 exp(-l2/l

02)

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

Minimal Spanning tree

define thresholds lt for maximum (over-dense) minimum (under-dense) length of branches l

t and

minimum number of objects in a domain M

3D: density of clusters with l ≥ lt is higher than

threshold density if

ρt <ρ><l3>/lt3

(strongly depends on the choice of l

t,M, determines

statistical significance)

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 acutoff length


MSTpruned to level 10 (branches k≤ 10 removed)

mean edge length:<lz> = 0.0215 rad (1.232°) and <l

r> = 0.0267 (1.530°)

random

MST: pruned and separated

cut-offs: 2<lz> and 1.6<l

r> 0.043 rad (3.142˚) separation in both cases

random

MST length distributions

frequency distribution of MST(Zwicky)shows excess of large and small l

zwicky

frequency distribution of MST (random) follows Gauss distributioncentered on <l

random>

random

length length

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 h3 Gpc3 ⇨~500 – 1000 Jumbo LQGs

morphologies: walls+blobs rather than filaments

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!)

<z> = 1.27

selection effect by objective-prism -- Ly-α emission shifted out of selection band at z>1.8

cover 2.5° x 5° on the sky

banana like structure

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 overdensitydiscovery of 2nd foreground LQG

Williger et al. 2002

Clowes-Campusano LQG Survey

Galaxy populations in LQGsLyman Break Galaxies (LBGs)red galaxy populationred sequence/blue cloud at z~1 in dense environment (colour-density inversion at z~1?)Quasar-galaxy correlations/feedback mechanism

Early Results 0.5º subfield: Red Galaxies

Haines et al. 2004

CTIO BTC 4m V,I data ~0.25 deg2 subfield31 x 27 h-2 Mpc2 at z ~ 1.2

3 x overdensity in red galaxies

2 x overdensity in red galaxies

dashed contours 1.65 gal. arcmin-2


2 x 1.2˚ GALEX FUV+NUV m

lim~24.0 mag

SDSS u,g,r,i,z~1.6˚ Bok g m

lim ~ 26 mag

2 x 1˚CFHT r+z mlim

~ 26 mag m

lim ~ 24 mag

~1.2˚KPNO 2.1m FLAMINGOS NIR J+Ks~1° UKIRT Ks-band

~600 Magellan IMACS spectra

Existing Data Set:

2

GALEX Medium Imaging Survey (used for WiggleZ bright LBGs)


Telescope Band Size expos. Time Status 3 AB limit

GALEX FUV,NUV 1.2 deg 21-39 ksec analyzed ~24.5 FUV,NUV

2.1m KPNO J, Ks 1.6x1.6 deg2 N: 7200s (J); 9600 (Ks) 75% reduced ~20 (J)

2.3m Bok g 1.2x1.2 deg2 N: 16800s reduced ~26.5

CFHT r,z 1 deg2 ~6000 sec r,z analyzed/09A N: ~27.5 (r), ~25.5 (z) S: ~27 (r), ~25.5 (z)

UKIRT Ks 1 deg2 ~4500sec obs 2/09

Survey Summary

Efficient search for z~1 galaxies

Lyman Break 912 Åat z~1

search for LBGs at z~1 using FUV-dropout technique

FUV

NUV

FUV-dropout examples:

FUV NUV SDSS

Lyman Break Galaxies (LBGs)

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.)


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 = galaxyresulting sample ~1000 LBG candidates


photometric redshift distribution

LBG candidates

LQG@z~0.8

CCLQG@z~1.3

dz = 0.05-0.10


Arnouts et al. (2005)

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

LBGs: old population component

SFHs of stacked/averaged LBG SEDsχ2-fit of averaged and normalized LBG SEDs to library of PÉGASE models

LQG@z~0.8 3 Gyr ≤ tbest

≤ 7 Gyr

CCLQG@z~1.3 3 Gyr ≤ t

best ≤ 7 Gyr

although fits with 250 ≤ t

youngest ≤ 800

are acceptable


results for best fitting ages show significant older t

best

than Burgarella et al. 2007 (250≤t

best≤500 Myr)

Burgarella sample include fainter LBGs younger star bursts younger averaged SEDs?

Our survey shallower, biased towardhigher mass LBGs?

~500 Myr

~250 Myr

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

QSOs on LBG Cluster Outskirts?

LBG concentrations + filamentsLBGs in proximity to QSOs QSO feedback mechanism?

z~0.8 Quasar-LBG correlations

117 LBGs, 17 quasars, 10000 random quasar placements

P=0.0027

P=0.0051,0.0056

1'~0.5 local Mpc

QSOs on (red) cluster outskirts?

red galaxies tend to avoid QSOs

formation of large filaments

Need better photometric redshifts (near-IR) to bin in redshift

Summary/Conclusions

1) Large quasar groups ~ quasar superclusters, useful laboratories for studying quasar-galaxy relations in large structure contexts

2) Clowes-Campusano LQG field being explored in 2 deg2 multi-wavelength survey

3) z~1 LBGs several Gyr old, older than only other study – due to shallower survey, more massive LBGs?

4) LBG-quasar correlation suggested to eye but does not show robust statistical signal (yet?) – need more data


Future Plans 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

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The Clowes-Campusano Large Quasar Group Survey