Lyman Break Galaxies in Large Quasar Groups at z~1

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Lyman Break Galaxies in Large Quasar Groups at z1

• 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)

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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

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Background LQGs

• Discovered late 1980s
• Shapes irregular, filamentary agglomerations
• Numbers 10-20 member quasars
• Sizes 100-200 Mpc ? not virialised
• Frequency 10-20 catalogued, but probably more
  in sky

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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 zlt0.4 (Söchting
  et al. 2004), analogous to star formation
  quenching
• Quasars at z1 preferentially in blue (U-Blt1)
  galaxy environments, presumably merger-rich (Coil
  et al. 2007, DEEP2)

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LQGs Structure Tracers

• Quasars AGN delineate structure at z0.3
  (Söchting et al. 2002)
• Quasar-galaxy correlation similar to
  galaxy-galaxy correlation (Coil et al. 2007)
• Quasars are most luminous structure tracers

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LQGs StructureStar Formation Probes

• At z1
• 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

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Clowes-Campusano LQG z1.3

• Discovered via objective prism survey, ESO field
  927 (104505) (Clowes et al. 1991, 94, 99 Graham
  et al. 1995)
• gt18 quasars Bjlt20.2, 1.2ltzlt1.4, overdensity of 6
  from SDSS DR3
• 2.5x5 (120x240 h-2 Mpc-2, H070 km s-1 Mpc,
  Om0.3, ?0.7)
• Overdensity of 3 in MgII absorbers (Williger et
  al. 2002)
• Overdensity of 30 in red galaxies (Haines et
  al. 2004)

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Bonus Foreground LQG z0.8

• gt14 quasars, 0.75ltzlt0.9, bright quasar
  overdensity 2
• 3x3.5 (100x120 h-2 Mpc-2)
• Marginal overdensity of MgII absorbers

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Clowes-Campusano (CC) LQG fieldSmall box CTIO
4m BTC field (VI)
- - - MgII survey
GALEX, CFHT imaging fields
z1.3 quasars O MgII absorbers z0.8 quasars O
MgII absorbers
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MgII overdensity
Shaded regions 65, 95, 99 confidence limits
based on uniform distribution of MgII absorbers
and selection function
CC LQG
z0.8 LQG
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Red Galaxy Overdensity

• Contours
• red galaxy
• density, V-I
• consistent
• with
• 0.8ltzlt1.4
• Boxes
• subfields
• observed in
• JK with ESO
• NTTSOFI

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LQG BRIGHT Quasar Overdensity

• Compare region to DEEP2 (4 fields, 3 deg2, Coil
  et al. 2007)
• No significant overdensity in CC LQG for moderate
  luminosity quasars to AGN -25.0ltMIlt-22.0
  (Richardson et al. 2004 SDSS photometric quasar
  catalogue)
• 3x overdensity for bright MIlt-25.0 quasars ?
  lots of merging

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Overdensity in bright quasars
2 deg2 11 bright, 34 faint quasars
3 deg2, 4 fields on sky 6 bright, 35 faint quasars
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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

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• NASA mission, launched 2003
• 1.2 circular field of view, imaging grism
• 50cm mirror, 6 arcsec resolution
• FUV channel 1500Å, NUV 2300Å

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• Surveys
• All sky 100 s exposure, AB20.5
• Medium imaging survey 1500s exp, 1000 deg2,
  AB23
• Deep imaging survey 30ks exp, 80 deg2, AB25
  OUR CONTROL (e.g. CDF-S, NOAO Wide Deep Survey,
  COSMOS, ELAIS, HDF-N)
• Ultra-deep imaging survey 200ks, 4 deg2, AB26
• NOTE confusion starts at NUV(AB)23
  deconvolution techniques with higher resolution
  optical data appear to work

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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 z1.0, M0.5 at z1.4
• FUV-NUV reveals Lyman Break Galaxies (LBGs) at
  z1 key star-forming population

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Completeness limits
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• GALEX NUV
• luminosity
• function and
• M (Arnouts
• et al. 2005)

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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 z3.0, in u-g bands
• UV flux strongly quenched (scattered) by dust
• LBGs only reveal fraction of star-forming galaxies

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Sloan Survey optical photometry

• For initial optical colours, use Sloan Digital
  Sky Survey 95 point source completeness u22.0,
  g22.2, r22.2, i21.3, z20.5 (Adelman-McCarthy
  et al. 2006)

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LBG sample in LQG

• FUV-NUVgt2.0 and NUVlt24.5
• 95 SDSS detections
• SDSS resolved as galaxies
• 7-band photo-z's of zgt0.5 (?z0.1)
• 690 candidates (50 of number density from
  Burgarella et al. 2007)

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GALEX, CTIO BTC, HST ACS close-up
? 28" ?
? 230 kpc ?
NUV
FUV
CTIO I
CTIO V
Possible merger in a z1 LBG
ACS F814W

• 80 kpc separation implies merger activity

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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

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Preliminary LBG auto-correlation

• Correlation
• length
• r013
• Mpc 3x
• stronger
• than NUV
• sample of
• Heinis et al.
• (2007), L
• galaxies at
• z1 and
• LBGs at z4
• Implies strong clustering

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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

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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
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Interpretation

• Strong LBG auto-correlation
• due to observing only brightest galaxies?
• Lack of quasar-galaxy clustering
• small number statistics?
• Best fit age gtgt 250-500 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

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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 z1 LBGs
  are red from Spitzer data. Is LQG population
  consistent?

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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 NTTSOFI, 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

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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

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SUMMARY

• Large quasar groups (LQGs) excellent tracers of
  star formation and large structures
• Largest, richest LQG at z1 observed with GALEX
  (FUVNUV) over 2 deg2
• 690 bright z1 LBGs
• Strong clustering r013 Mpc
• Mean ages best fit 2.5Gyr, but 120Myr allowed
• Working with ground-based data, proposing deeper
  GALEX exposures to probe down luminosity function