RedSequence Galaxies with young stars and dust The

Red-Sequence Galaxies with young stars and dust The cluster A 901/902 seen with COMBO-17 Christian Wolf (Oxford) Meghan E. Gray (Nottingham) Klaus Meisenheimer (Heidelberg) A&A, in press

Testing ground: the A 901/902 supercluster A 901 a A 901 b A 902 z=0. 16: ~5 x 5 Mpc A 902

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

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

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

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

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

Selecting The Cluster Sample zphot = 0. 170 ± 0. 006 cz = 1900 km/s 795 galaxies within 1575 = 3. 7 x 3. 5 x 120 (Mpc/h)3

Field Sample COMBO-17 field @ 0. 05<z<0. 25 excluding overdensities 385 galaxies from 9750 (Mpc/h)3 with <z>=0. 172

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)

2 -D Family: Age x Extinction

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

Dust-free old clump Dusty red contaminants Blue cloud

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

Old vs. Dusty Near 4000 A

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

Mean Spectra

Ratio Spectrum: Dusty/Old

Population Mix: Cluster / Field Enhanced / redder

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

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

Luminosity Distribution

Type-Density Relation field cluster

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

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

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

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

Outlook: Spitzer 24 Analysis • Most EB-V>0. 2 red-sequence galaxies are luminous 24 sources • Bell et al. in prep.

Outlook: Morphology WFI@2. 2 COMBO-17 HST/ACS STAGES Gray et al.

STAGES: Center of A 901 a WFI@2. 2 HST/ACS