Lyman Break Galaxies in Large Quasar Groups at z~1 G Williger (Louisville/JHU), R Clowes (Central Lancashire), L Campusano (U de Chile), L Haberzettl & J Lauroesch (Louisville), C Haines (Naples,Birmingham), J Loveday (Sussex), D Valls-Gabaud (Meudon), I Söchting (Oxford), R Davé (Arizona), M Graham (Caltech)

Outline Background on large quasar groups (LQGs) Clowes-Campusano LQG Observations: –Galaxy Evolution Explorer (GALEX), Lyman Break Galaxies –SDSS for Ground-based wide-field imaging Analysis, interpretation Conclusions/further work

Background: LQGs Discovered: late 1980s Shapes: irregular, filamentary agglomerations Numbers: ~10-20 member quasars Sizes: Mpc  not virialised Frequency: ~10-20 catalogued, but probably more in sky

Why Study LQGs? Star Formation Quasars likely triggered by gas-rich mergers in local (~1 Mpc) high density environments (Ho et al. 2004; Hopkins et al. 2007) –Quasars avoid cluster centres at z~<0.4 (Söchting et al. 2004), analogous to star formation quenching –Quasars at z~1 preferentially in blue (U-B<1) galaxy environments, presumably merger-rich (Coil et al. 2007, DEEP2)

LQGs: Structure Tracers Quasars + AGN delineate structure at z~0.3 (Söchting et al. 2002) Quasar-galaxy correlation similar to galaxy-galaxy correlation (Coil et al. 2007) Quasars are most luminous structure tracers

LQGs: Structure+Star Formation Probes At z~1 –star formation much higher than present  quasars should mark regions of high star formation –Galaxy surveys time-intensive  more efficient to use quasars as structure markers

Clowes-Campusano LQG z~1.3 Discovered via objective prism survey, ESO field 927 ( ) (Clowes et al. 1991, 94, 99; Graham et al. 1995) >=18 quasars Bj<20.2, 1.2<z<1.4, overdensity of 6 from SDSS DR3 2.5°x5° (120x240 h -2 Mpc -2, H 0 =70 km s -1 Mpc, Ω m =0.3, Λ=0.7) Overdensity of 3 in MgII absorbers (Williger et al. 2002) Overdensity of ~30% in red galaxies (Haines et al. 2004)

Bonus: Foreground LQG z~0.8 >=14 quasars, 0.75~<z~<0.9, bright quasar overdensity ~2 ~3°x3.5° (100x120 h -2 Mpc -2 ) Marginal overdensity of MgII absorbers

Clowes- Campusano (CC) LQG field Small box: CTIO 4m BTC field (VI) z~1.3 quasars O MgII absorbers z~0.8 quasars O MgII absorbers MgII survey GALEX, CFHT imaging fields

MgII overdensity CC LQG Shaded regions: 65, 95, 99% confidence limits based on uniform distribution of MgII absorbers and selection function z~0.8 LQG

Red Galaxy Overdensity Contours: red galaxy density, V-I consistent with 0.8<z<1.4 Boxes: subfields observed in JK with ESO NTT+SOFI

LQG: BRIGHT Quasar Overdensity Compare region to DEEP2 (4 fields, 3 deg 2, Coil et al. 2007) No significant overdensity in CC LQG for moderate luminosity quasars to AGN <M I <-22.0 (Richardson et al SDSS photometric quasar catalogue) ~3x overdensity for bright M I <-25.0 quasars  lots of merging

Overdensity in bright quasars ~2 deg 2 11 bright, 34 faint quasars 3 deg 2, 4 fields on sky 6 bright, 35 faint quasars

CC LQG: Unique Laboratory Deep fields (DEEP2, Aegis etc.) NOT selected for quasar overdensity Clowes-Campusano LQG: UNIQUE opportunity to study galaxies and quasar- galaxy relation in DENSE quasar environment

NASA mission, launched ° circular field of view, imaging + grism 50cm mirror, 6 arcsec resolution FUV channel: ~1500Å, NUV: ~2300Å

Surveys: –All sky: 100 s exposure, AB~20.5 –Medium imaging survey: 1500s exp, 1000 deg 2, AB~23 –Deep imaging survey: 30ks exp, 80 deg 2, AB~25 – OUR CONTROL (e.g. CDF-S, NOAO Wide Deep Survey, COSMOS, ELAIS, HDF-N) –Ultra-deep imaging survey: 200ks, 4 deg 2, AB~26 –NOTE: confusion starts at NUV(AB)~23 – deconvolution techniques with higher resolution optical data appear to work

UV Observations GALEX: 2 overlapping ~1.2° fields Exp times ~21-39 ksec, 70-90% completeness for AB mags ~24.5 in FUV, NUV –M* at z~1.0, M*+0.5 at z~1.4 FUV-NUV reveals Lyman Break Galaxies (LBGs) at z~1 – key star-forming population

Completeness limits

GALEX NUV luminosity function and M* (Arnouts et al. 2005)

Lyman Break Galaxies (LBGs) Break at rest-frame Lyman Limit 912Å sign of intense star formation –Often associated with merger activity Easily revealed in multi-band imaging –First found at z~3.0, in u-g bands UV flux strongly quenched (scattered) by dust –LBGs only reveal fraction of star-forming galaxies

Sloan Survey: optical photometry For initial optical colours, use Sloan Digital Sky Survey: 95% point source completeness u=22.0, g=22.2, r=22.2, i=21.3, z=20.5 (Adelman-McCarthy et al. 2006)

LBG sample in LQG FUV-NUV>=2.0 and NUV<=24.5 –95% SDSS detections SDSS resolved as galaxies 7-band photo-z's of z>0.5 (Δz~0.1) 690 candidates (~50% of number density from Burgarella et al. 2007)

GALEX, CTIO BTC, HST ACS close-up ~80 kpc separation implies merger activity Possible merger in a z~1 LBG FUV NUV CTIO V ACS F814W CTIO I  28"   230 kpc 

LBG Auto-correlation, LBG-quasar clustering Preliminary Limber inversion of LBG power law auto-correlation –Evidence for strong clustering No significant overdensity of LBGs around 13 brightest quasars

Preliminary LBG auto-correlation Correlation length r 0 =13 Mpc: 3x stronger than NUV sample of Heinis et al. (2007), L* galaxies at z~1 and LBGs at z~4 – Implies strong clustering

Mean Galaxy Ages Calculate mean, std dev of rest-frame LBG 7-band photometry Fit spectral energy distributions (SEDs; PEGASE, Fioc & Rocca-Volmerange 1997) –Closed-box models  metallicity not free parameter –Dust and dust-free models used

Mean LBG galaxy ages Most promising constraint for galaxy ages from highest z bin Best fit: 2.5 Gyr, exponentially decreasing SFR with decay time 5 Gyr (no dust) Youngest acceptable fit: 120 Myr burst model (with dust) Only 64 galaxies in this z-bin

Interpretation Strong LBG auto-correlation –due to observing only brightest galaxies? Lack of quasar-galaxy clustering –small number statistics? Best fit age >> Myr found by Burgarella et al. toward CDF-South –Due to our observing only brightest, most massive galaxies? –Burgarella et al sample went 2x deeper in UV, has COMBO-17, Spitzer, Chandra supporting data

Questions to address Does blue galaxy environmental preference of Coil et al. persist to same degree in LQG? Burgarella et al. (2007) found 15% of z~1 LBGs are red from Spitzer data. Is LQG population consistent?

Ground-based Supporting Data 2x1° imaging in rz (CFHT Mega-Cam) ~1.5° imaging in gi (Bok 2.3m) ~1° imaging in JK (KPNO 2.1m) ~0.5° imaging VRIz (CTIO 4m) – away from GALEX fields around group of 4 LQG members ~600 redshifts from Magellan 6.5m 5 subfields in JK with NTT+SOFI, additional MgII spectra with VLT, 30' subfield in VI with CTIO 4m Proposed Chandra images of bright quasars  search for hot gas in rich clusters

Further work Reduce, analyse deeper optical-IR images –Individual galaxy SEDs, better discrimination on red end –Search for red-selected galaxies Use Magellan spectra, observed near-IR bands for better photo-z's Proposed deeper (2x) exposures for GALEX Cy4 Will propose for Spitzer to get evolved stellar populations

SUMMARY Large quasar groups (LQGs): excellent tracers of star formation and large structures Largest, richest LQG at z~1 observed with GALEX (FUV+NUV) over 2 deg bright z~1 LBGs –Strong clustering: r 0 ~13 Mpc –Mean ages best fit ~2.5Gyr, but 120Myr allowed Working with ground-based data, proposing deeper GALEX exposures to probe down luminosity function