Life Before the Fall:
Group Galaxy Evolution Prior to
Cluster Assembly
Anthony Gonzalez (Florida)
Kim-Vy Tran (CfA)
Michelle Conbere (Florida)
Dennis Zaritsky (Arizona)
John Moustakas (Arizona)
Hierarchical Assembly: SG1120
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Detection:
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Las Campanas Distant Cluster Survey (Gonzalez et al. 2001)
4 candidates at z~0.4 within
a 7’ diameter region
Confirmation:
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Chandra + spectroscopy
6 extended sources within a 13’
diameter region (~4 Mpc)
Groups at z=0.37 (2,3,4,5)
Cluster at z=0.48 (1)
No redshift yet (6)
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“Supergroup” SG1120-1202
Ringberg Workshop - October 25, 2005
Hierarchical Assembly: SG1120
3
VLT
BVR
Imaging
4
Ringberg Workshop - October 25, 2005
Spectroscopic Confirmation
VLT
Spectroscopy
101 confirmed
members
Ringberg Workshop - October 25, 2005
Redshift Distribution
Dispersions
All
62050 km/s
Group 3
Group 4
Group 5
37080 km/s
45080 km/s
56090 km/s
Merging Galaxy Groups
``Virialized’’ Halos
Gonzalez et al. 2005
Ringberg Workshop - October 25, 2005
Mass and Dynamics
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Mass
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Tx (sum of individual groups 2-5): 5x1014 M
- lower limit
Dynamical Analysis
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Gravitationally bound
Should merge by z~0
Additional velocities for groups 2,6 will refine this constraint
Should evolve in to a Coma-ish cluster by z=0
Ringberg Workshop - October 25, 2005
Galaxy Evolution in Groups
Coma Cluster (z~0.02)
SG1120 (z=0.37)
Coma Progenitor
Ringberg Workshop - October 25, 2005
Galaxy Evolution in Groups
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Key Questions
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Morphological Evolution
Quenched/Enhanced Star Formation
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Galaxy Mass Assembly
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E+A’s
Fraction of star-forming galaxies; total star formation rate
HOD
Interaction Rate
Wet/Dry Mergers
Relation of above quantities to local density and galaxy mass
Ringberg Workshop - October 25, 2005
Galaxy Evolution in Groups
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Method
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Morphological Evolution (ACS - 10 orbit F814 mosaic)
Quenched/Enhanced Star Formation
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Galaxy Mass Assembly
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E+A’s
(VIMOS spectra, MIPS 24 m)
Fraction of star-forming galaxies; total star formation rate
HOD
Interaction Rate
Wet/Dry Mergers
(BVRJKS, ACS+WFPC2)
Relation of above quantities to local density and galaxy mass
(Chandra, ACS, BVRJKs imaging, MIPS, spectroscopy)
Ringberg Workshop - October 25, 2005
Color-Magnitude Diagram
Established Red Envelope
Retains Population of
Starforming Galaxies
Foreground/Background
F
Intermediate between
Field/Clusters
Ringberg Workshop - October 25, 2005
Passive Fraction
Pre-processing
618% passive
- Roughly twice as many
as field (same z)
Ringberg Workshop - October 25, 2005
Member Galaxies and Interactions
Ringberg Workshop - October 25, 2005
Summary
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SG1120 is a confirmed “supergroup” at z=0.37
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Gravitationally bound system
4-5 member groups within target region
Direct view of progenitors of massive cluster
Well-defined red envelope
Strong correlation between surface density and
passive fraction
Ongoing mergers of massive galaxies, high merger
fraction
Ringberg Workshop - October 25, 2005
Work in Progress
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ACS Mosaic (10 orbit F814W)
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MIPS - dusty star formation
Additional spectroscopy
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Morphological fractions and morphology-density relation
Interaction rate
E+A fraction
Fundamental plane
Finish mapping superstructure
ACS+Chandra+spectra
Cross-correlation between local density and X-ray surface
brightness
 SED and morphology vs X-ray surface brightness
Comparison with properties of both local clusters (Coma) and CL 1358
(z=0.33)
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Ringberg Workshop - October 25, 2005