The Star Formation- Density Relation

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The Star Formation-Density Relation and the
Cluster Abell 901/2 in COMBO-17

• Christian Wolf (Oxford)
• Eric Bell, Anna Gallazzi, Klaus Meisenheimer
  (MPIA Heidelberg)
• Alfonso Aragon-Salamanca, Meghan E. Gray, Kyle
  Lane (Nottingham)

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Morphology-Density Relation

• Morph-density relation
• Present when averaged over age/colour (Dressler
  1980)
• No such relation
• at fixed colour or age (Ball, Loveday Brunner
  2006 Wolf et al. 2007)
• at fixed mass(Kauffmann et al. 2004)
• SFR-/Age-density relation
• Yes at fixed mass(Balogh et al. 1999 Kauffmann
  et al. 2004 Poggianti et al. 2006)
• Yes at fixed morphology(Wolf et al. 2007)

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Morphology-Age-Density

• Age-density relation for ageing (E-Sb)
  galaxies
• Age-morphology relation for fixed density
  (obvious?!)
• No Morphology-density relation at fixed age

Wolf et al. 2007
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SF-Density (?) Relation

• Stripping (Ram press., Gun Gott 72)
• Excitation (Tidal of burst, Bekki 99)
• Harassment (Moore et al. 1999)
• Mergers (Major, Barnes 1992)
• Suffocation (Larson 1980)
• Strangulation (Balogh et al. 2000)

• Nature?
• Internal feedback (SN, AGN)

• or nurture?

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SF-Density Relation Across Z

• Present-day SF-density
• Optical SF indicators
• GOODS (Elbaz et al. 2007)
• z1, includes obscured SF
• SF peaks at higher density
• Semi-analytic simulations
• Typically include mergers, but no environment
  physics
• Recent work IGM heating ram-pressure
  stripping(Khochfar Ostriker 2007)

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Low-Z incl. Obscured SF

• Obscured SF different result from UV-optical
  indicators
• COMBO-17 A901 MIPS
• Obscured SF continues into high-density regions
• Not very different to z1
• Which galaxies make the difference?
• See dusty red galaxies (Wolf, Gray
  Meisenheimer 2005)

(MBlt-20)
A901
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COMBO-17 on A901 Complex

• Disturbed evolving cluster Abell 901a/b 902
• Galaxy transformation during plenty of infall
  action
• 800 cluster members with MV lt -17.8 and ?z 0.006

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Old Red / Dusty Red _at_ z0.17
Age ?
Dust ?
Wolf, Gray Meisenheimer 2005
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Mean Spectra
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Type-Density Relation

• Dusty red galaxies
• Intermediate ages
• Intermediate density
• Intermediate luminosity
• Intermediate morphology
• Non-virialized kinematics ? infall
  population?

WGM 2005
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Optically Passive Spirals!

• Passive spirals(Poggianti et al. 1999 Goto et
  al. 2003)
• Spectra coloursLack of star formation
• Cluster infall regions
• Might be intermediate stage from spiral to S0
• A901 dusty red galaxies (Wolf, Gray
  Meisenheimer 2005)
• 35(!) of red members
• Red star-forming galaxies(Miller Owen 2002,
  Coia et al. 2005)
• Radio ISO 15?
• Outskirts of merging cluster

blue
old
dusty
E
S0
Sa
Sb
Sc
Sd
Irr
The STAGES collaboration
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SFR UV-opt. vs. Obscured
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Dust Extinction IR/UV Ratio
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Dusty Red Transition Population

• Dusty red galaxies in A901
• are semi-suppressed in star formation
• have star formation obscured to highest degree
• star formation obscuration stellar light
  obscuration
• All galaxies appear to follow a 2 Gyr exponential
  SFR decline

15
IR-Semi-Passive Galaxies

• Transition galaxies
• IR-semi-passive spirals
• 1/2-dex-reduced central dust-extinguished SF
• No burst upon infall
• No sign of major mergers
• No truncation (H? weak)
• Where found?
• In three complex merging cluster environments(so
  far)

• Star formation budget
• Fraction of obscured SF increases in infall
  region
• Small on cosmic scale
• Relevant for role of environment
• Continued central SF may continue bulge growth

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Suggestions Observations

• Quenching Timescale?
• High-S/N spectra SED
• Recent SF History

• More (super-) clusters?
• Density is not only factor
• 2nd parameter Stage of infall, cluster
  merging?
• Optical SED sufficient(?)
• Need
• Redshift coverage
• Range of environments
• Accurate dust estimates or Mid-IR imaging
• Medium-band photo-zs or spectroscopy

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Space Telescope A901/902 Galaxy Evolution Survey

• 80 orbit mosaic
• ACS WFPC2/NIC3 parallels
• multiwavelength follow-up from X-ray to radio
• primary science aim galaxy evolution as a
  function of environment

image COMBO-17
contours mass
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(No Transcript)
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Ratio Spectrum Dusty/Old
WGM 2005
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Selecting The Cluster Sample
zphot 0.170 0.006
795 galaxies within ?cz 1900
km/s 1575 3.7 x 3.5 x 120 (Mpc/h)3
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Luminosity Distribution
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2-D Clustering
Old red cluster cores Dusty red blue cloud
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(x,y) old red cluster cores dusty red blue
cloud
(y,z) old red dusty red blue cloud voids
?v 550 km/s
?v 1400 km/s