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

This study examines the relationship between star formation and density in the Abell 901/2 cluster using the COMBO-17 survey data. It explores various factors such as morphology, age, and obscuration, and investigates different mechanisms that affect star formation in dense environments.

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

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  1. 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)

  2. 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)

  3. 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

  4. Gomez et al. 2002 (SDSS) Kodama et al. 2001 Lewis et al. 2002 (2dF) SF-Density () Relation …or nurture? • 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)

  5. SF-Density Relation Across Z • Present-day SF-density • Optical SF indicators • GOODS (Elbaz et al. 2007) • z~1, 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)

  6. Gallazzi et al., in prep. 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 z~1 • Which galaxies make the difference? • See dusty red galaxies (Wolf, Gray & Meisenheimer 2005) (MB<-20) A901

  7. QE (%) 5 Mpc λ/ nm COMBO-17 on A901 Complex • Disturbed evolving cluster Abell 901a/b & 902 • Galaxy transformation during plenty of infall action • 800 cluster members with MV < -17.8 and z ~ 0.006

  8. Old red Dusty red~150 atMV<-18 Old Red / Dusty Red @ z=0.17 Age  Dust  Wolf, Gray & Meisenheimer 2005

  9. Mean Spectra

  10. Type-Density Relation • Dusty red galaxies: • Intermediate ages • Intermediatedensity • Intermediate luminosity • Intermediate morphology • Non-virialized kinematics infall population? WGM 2005

  11. Optically Passive Spirals! • Passive spirals(Poggianti et al. 1999; Goto et al. 2003) • Spectra & colours:Lack 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

  12. SFR: UV-opt. vs. Obscured

  13. Dust Extinction & IR/UV Ratio

  14. 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 galaxiesappear to follow a 2 Gyr exponential SFR decline

  15. 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 IR-Semi-Passive Galaxies

  16. 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-z’s or spectroscopy Suggestions: Observations

  17. 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

  18. Ratio Spectrum: Dusty/Old WGM 2005

  19. 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

  20. Luminosity Distribution

  21. 2-D Clustering Old red = cluster cores Dusty red ~ blue cloud

  22. (x,y): old red = cluster cores dusty red ~ blue cloud (y,z): old red ~ dusty red blue cloud = ‘voids’ v ~ 1400 km/s v ~ 550 km/s

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