The The Star Formation-Star Formation-Density Relation Density Relation

…and the Cluster Abell 901/2 in COMBO-17…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)

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)

Morphology-Age-Density

Wolf et al. 2007

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

SF-Density () Relation

Gomez et al. 2002 (SDSS)

Kodama et al. 2001

Lewis et al. 2002 (2dF)

…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)

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)

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)

A901Gallazzi et al., in prep.

λ / nm

QE (

%)

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

5 Mpc

Old Red / Dusty Red @ z=0.17

Age

Dust

Old red

Dusty red

~150 atMV<-18

Wolf, Gray & Meisenheimer 2005

Mean Spectra

Type-Density RelationDusty red galaxies:

• Intermediate ages• Intermediate density• Intermediate luminosity• Intermediate morphology

• Non-virialized kinematics infall population?

WGM 2005

Optically Passive Spirals!

old

dusty

blue

E S0 Sa Sb Sc Sd Irr

The STAGES collaboration

• 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

SFR: UV-opt. vs. Obscured

Dust Extinction & IR/UV Ratio

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

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

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-z’s or spectroscopy

• 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

Space Telescope A901/902 Galaxy Evolution Survey

Ratio Spectrum: Dusty/Old

WGM 2005

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

Luminosity Distribution

2-D Clustering

Old red = cluster coresDusty red ~ blue cloud

(x,y): old red = cluster coresdusty red ~ blue cloud

(y,z): old red ~ dusty redblue cloud = ‘voids’

v ~ 550 km/sv ~ 1400 km/s