1. Red-Sequence Galaxies with young stars and dust The cluster A901/902 seen with COMBO-17 Christian Wolf (Oxford) Meghan E. Gray (Nottingham) Klaus Meisenheimer (Heidelberg) A&A, in press

2. A901a A901b A902 Testing ground: the A901/902 supercluster z=0.16: ~5x5 Mpc

3. COMBO-17 SEDs SED classification ~98% complete at R<23 –Stars (~2000)

4. COMBO-17 SEDs SED classification ~98% complete at R<23 –Stars (~2000) –White Dwarfs (13)

5. COMBO-17 SEDs SED classification ~98% complete at R<23 –Stars (~2000) –White Dwarfs (13) –Galaxies (~6000)

6. COMBO-17 SEDs SED classification ~98% complete at R<23 –Stars (~2000) –White Dwarfs (13) –Galaxies (~6000) –QSOs (~100)

7. Redshift Accuracy But first photo-z trials in 2002: 1/4 galaxies wrong!!!

8. Selecting The Cluster Sample z phot = 0.170 ± 0.006 795 galaxies within  cz = 1900 km/s1575 = 3.7 x 3.5 x 120 (Mpc/h) 3

9. Field Sample COMBO-17 field @ 0.05<z<0.25 excluding overdensities 385 galaxies from 9750 (Mpc/h) 3 with =0.172

10. Colour-Magnitude Diagram COMBO-17 evolving red-sequence fit @ 0.2<z<1.2 795 galaxies = 462 red-sequence + 333 blue-cloud (field: 62=13+49)

11. 2-D Family: Age x Extinction

12. What is in the Red Sequence? Examine age x extinction diagram Try splitting red-sequence: –Dust-free old clump Cleaner sample of old red galaxies –Dusty contaminants What are these? Blue cloud as usual Regular star-forming galaxies

13. Dust-free old clump Dusty red contaminants Blue cloud

14. Templates: Old vs. Dusty Red Dusty red galaxies are - redder at red end - bluer at blue end than old red galaxies

15. Old vs. Dusty Near 4000A

16. Mean Spectra: Old / Dusty Trends in continuum colour and spectral lines!

17. Mean Spectra

18. Ratio Spectrum: Dusty/Old

19. Population Mix: Cluster / Field Enhanced / redder

20. 2-D Clustering Old red = cluster cores Dusty red ~ blue cloud

21. (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

22. Luminosity Distribution

23. Type-Density Relation field cluster

24. A “Third Party”(??)… Three types of galaxies: 1.Old red, passively evolving 2.Intermediate 3.Young blue, actively star-forming Intermediate properties –Ages: intermediate or “old + young” –Star formation: Little but present –Colour: like red / Dust: like blue galaxies –Luminosities: intermediate –Habitat: medium-density preferred Small contribution from edge-on disks

25. Origin of Intermediate Type Transformed infalling blue galaxies: Contra: –Luminosity of progenitors –High mean stellar ages Age sequence: cores - intermediates - outskirts - field Pro: –Spirals redder as well (Butcher-Oemler effect) Minor mergers: established large old cluster elliptical +infalling small blue galaxy Pro: –Properties fine without invoking special process –High-luminosity and old-age component required Contra: –Very few undisturbed established old cluster ellipticals in outskirts left

26. Summary: Data & Galaxy Types COMBO-17 surveys dynamically complex supercluster Abell 901/902 photo-z’s provide ~800 galaxies at M V <-17 Detailed 17-band SED - age x extinction grid More than 1/3 of the red-sequence are not old red galaxies, but dustier intermediate-age ones Added complexity in colour-density relation: dusty red galaxies don’t conform with old red or young blue

27. Summary: Properties of Dusty Red Galaxies Peak at mid-density (40%) Form interface between blue and old red Currently forming stars Have plenty of old stars Result of –Environmentally triggered transformation of infalling blue galaxies –Age sequence –Minor merger of infalling blue galaxy into old red cluster elliptical

28. Outlook: Spitzer 24  Analysis Most E B-V >0.2 red-sequence galaxies are luminous 24  sources Bell et al. in prep.

29. Outlook: Morphology WFI@2.2 COMBO-17 HST/ACS STAGES Gray et al.

30. STAGES: Center of A901a WFI@2.2HST/ACS