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
The Clowes-Campusano LQG Survey
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
The Clowes-Campusano LQG Survey
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)
The Clowes-Campusano LQG Survey
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.)
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 = galaxyresulting sample ~1000 LBG candidates
The Clowes-Campusano LQG Survey
photometric redshift distribution
LBG candidates
LQG@z~0.8
CCLQG@z~1.3
dz = 0.05-0.10
The Clowes-Campusano LQG Survey
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
The Clowes-Campusano LQG Survey
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
The Clowes-Campusano LQG Survey
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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