Red-Sequence Galaxies with young stars and dust

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 A901a A901b A901b A902 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 zphot = 0.170 ± 0.006 795 galaxies within cz = 1900 km/s 1575 = 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 <z>=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 ofold red galaxies • Dusty contaminants • What are these? • Blue cloud as usual • Regular star-forminggalaxies

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 ~ 1400 km/s v ~ 550 km/s

22. Luminosity Distribution

23. Type-Density Relation field cluster

24. A “Third Party”(??)… • Three types of galaxies: • Old red, passively evolving • Intermediate • 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. 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 Origin of Intermediate Type

26. Summary: Data & Galaxy Types • COMBO-17 surveys dynamically complex supercluster Abell 901/902 • photo-z’s provide ~800 galaxies at MV<-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 EB-V>0.2 red-sequence galaxies are luminous 24 sources • Bell et al.in prep.

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

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