Star formation activity as a function of z and

environment

DISTANT CLUSTERS OF GALAXIES

Ringberg, 24-28 October 2005

Bianca Maria Poggianti

INAF – Osservatorio Astronomico di Padova

P.I. S. White ( MPA-Garching, D )A. Aragón-Salamanca ( Nottingham, UK )R. Bender ( Munich, D )P. Best ( ROE, Scotland )M. Bremer ( Bristol, UK )S. Charlot ( MPA, D & IAP, F )D. Clowe ( Bonn, D)J. Dalcanton ( U.Washington, USA )B. Fort ( IAP, F )P. Jablonka ( OPM, F )G. Kauffmann ( MPA, D )Y. Mellier ( IAP, F )R. Pello ( OMP, F )B. Poggianti ( Padova, I )

H. Rottgering ( Leiden, NL )P. Schneider ( Bonn, D )D. Zaritsky ( U. Arizona, USA )M. Dantel ( OPM, F )G. De Lucia ( MPA, D )V. Desai ( U. Washington, USA )C. Halliday ( Padova, I )B. Milvang-Jensen ( MPE, D )S. Poirier ( OPM, F )G. Rudnick ( MPA, D )R. Saglia ( Munich, D )L. Simard ( U. Victoria, C )J. Varela ( Padova, I)

The ESO Distant Cluster Survey (EDisCS)

Study evolution of cluster galaxies and clusters in 20 fields with clusters at z=0.4 – 1.0

CL1202.4-1224

z=0.42

EDisCS Imaging

CL1232.3-1250z=0.54

CL1037.5-1243

z=0.58

CL1054.4-1245

z=0.75

CL1354.1-1231

z=0.76

THE DATASET

• Deep imaging: VRIJK at z~0.8, BVIK at z~0.5 (FORS2/VLT + SOFI/NTT) (White et al. 2005)

• HST/ACS imaging for 10 most distant clusters (80 orbits)

• WFI/2.2m RVI imaging for all 20 fields

• XMM data for >=3 clusters

• Spectroscopy: at least 4 FORS2 masks/cluster at long exposure to get spectra to I~23 (z~0.8) or 22 (z~0.5)

Spectroscopy25 nights of FORS2 MXU spectroscopy average of 35 members/cluster

z’s to I~23 (over ~3.5mag)

Line strength to I~22.5

’s to I~21.5

Halliday et al. 2004

Redshifts, σ’s +substructure analysis

Halliday et al. 2004 and Milvang-Jensen et al. in prep.Spectroscopy: the sample

Halliday et al. 2004 and Milvang-Jensen et al. in prep.Spectroscopy: the sample

For this work, 16 clusters, 10 groups and 250 galaxies in poor groups and the “field”.

Star formation

Star-formation histories

Deriving the fraction of star-forming galaxies

Galaxies with EW(OII)>3 Å

Non trivial:

no bias in galaxy sample

corrected for completeness

within R200 (mean density 200 times the critical density) and to appropriately evolving galaxy magnitude limits

good spectral quality and sufficient number of spectra per cluster

Poggianti et al. submitted

EDisCS: [OII] – sigma relation

Most clusters on a stripe

Outliers

Anticorrelation or upper envelope?

At a given cluster σ, AT MOST a given % of star-forming galaxies – or AT LEAST a certain % of passive galaxies

Suggests dependence SF-Mass of the system, but might well be a secondary relation – density? (e.g. existence of outliers) Velocity dispersion

z = 0.4 to 0.8

Fra

ctio

n o

f me

mb

ers

with

OII

with

in R

20

0

1000500

Fraction of galaxies with [OII] emission

Residuals of the OII relation with redshift

Redshift

Re

sid

ual

s fr

om

OII-

sig

ma

rel

atio

n

Evolution with z of the % of SF-ing galaxies

EDisCS: z = 0.4-0.8 Sloan (Abell): z = 0.04-0.1

The fact that distant clusters contain more SFing galaxies than nearby clusters is not new of course. But for the first time, evolution is quantified as a function of the system mass

At z=0, trend with sigma remains only at < 500 km/s ?

Sloan C4 (Miller et al. 05) sample: z = 0.04-0.08

Evolution with z of the % of SF-ing galaxies

EDisCS: z = 0.4-0.8 Sloan (Abell): z = 0.04-0.1

These results might explain why it has been difficult to detect and quantify evolution (eg Kodama et al. 2004, Finn et al. 2004,2005, Nakata et al. 2005) and the apparently constrating results regarding the presence (Martinez et al. 2002, Biviano et al. 1997, Zabludoff & Mulchaey 1998, Margoniner et al. 2001) or absence (eg Ellingson et al.2001, Smail et al. 1998, Goto 2005, Wilman et al.2005) of clear correlations with global cluster properties

Evolution of the OII-sigma relation

How are these trends established?

Why a general trend at z=0.8, and a broken one at z=0? What is special about a 500 km/s system at z=0?

Field Poor groups

0.4 0.8 0.4 0.8

Other environments:

Redshift distributions

GROUPS -- > 7 spectroscopic members, measured sigma

POOR GROUPS - 3 to 6 spec. members, no sigma

FIELD – anything not in clusters, groups or poor groups

EDisCS: [OII] – sigma relation

Fraction of galaxies with [OII] emission

Cluster velocity dispersion

Z=0.4 to 0.8

Groups “close” to clusters different from “isolated” groups? Another hint for density?

EW(OII) distributions in different environments

The % of starforming galaxies changes with environment and z

Does the SF activity in SFing galaxies change with environment? (only EDisCS)

The EW([OII]) distribution is more skewed towards high values in environments with higher [OII] fractions.

We find that BOTH the EWs at a given L and the luminosity distribution of SFing galaxies vary with environment.

Star formation vs Hubble type

Hubble types; visual classification from HST images (10 clusters, Desai et al.)

Early/Late types: B/D decomposition from VLT images (all 20 fields, Simard et al.)

Desai et al. in prep.

EDisCS: Galaxy morphologies with HST

Redshift

Sp

+Ir

r %

E

+S

0 %

S0

%

E

%

0.80.0

Evolution from spirals to S0s in clusters (Dressler et al. 1997, Fasano et al. 2000, Treu et al. 2003, Postman et al. 2005, Smith et al. 2005)

Morphology-density at z~1

Postman et al. 2005

projected density

f_S

p+

Irr

f

_S

0

f_

E

f_E

+S

0

STAR-FORMATION versus MORPHOLOGY

SF-ing: SF-ing spirals (85%) Spirals: SF-ing spirals (87%) and

and SF-ing E+S0s (15%) passive spirals (13%)

Sp

+Ir

r

E+

S0

S

0

E %

The origin of the observed trends:

star formation activity and structure growth

Origin of the OII-sigma relation

Two families of passive galaxies:

“primordial” passive galaxies that completed their SF at z>2

“quenched” galaxies that stopped forming stars after they entered the dense environment for the first time

If SF depends on the mass of the system, there should be a connection between the SF trends and the growth history of structures

Press-Schechter (Bower 1991, Lacey & Cole 1993) for mass fraction Millennium Simulation (Springel etal 05,De Lucia et al. 2005) for galaxy fraction

HIGH REDSHIFT (z=0.4-0.8)

The fraction of passive galaxies observed at high-z agrees with the fraction of mass/galaxies that were already in groups (M > 3 X 10^12) at z=2.5

When primordial galaxies finished forming stars (z>2), the most massive systems were groups (M > 3 X 10^12)

LOW REDSHIFT

The fraction of passive galaxies observed at low-z agrees with the fraction of galaxies in clusters (M > 10^14) at z~0.28 (3 Gyr before observations)

Of these, 20% are primordial passive galaxies and 60% are quenched galaxies

“Group” environment (M << 10^14) cannot efficiently and universally quench star formation

the break at ~500 km/s observed at z=0 corresponds to M~10^14 :reference mass for efficient quenching

3 Gyr a reasonable upper limit for quenching timescale

SUMMARY

The [OII]-sigma relation suggests that at high-z the proportion of star forming galaxies largely depends on the mass of the system (mass or density?)

Significant evolution in the star forming fraction between z=0.8 and z=0 in clusters and groups, and quantify evolution as a fn. of sigma

At z=0, no trend of [OII] fraction with sigma above ~500 km/s

At high redshift also the EW([OII]) distributions vary systematically with environment

The evolution of the star forming fraction is consistent with the evolution of the fraction of spirals

CONCLUDING REMARKS Possible link between the star formation activity in galaxies and the history of growth of clusters and groups:

In a scenario in which the passive galaxy populations have two components (primordial and quenched galaxies):

consistency between fractions of passive galaxies at high-z and expected fractions of mass/galaxies already in groups at z=2.5

consistency between fractions of passive galaxies at low-z and expected fractions of mass/galaxies that have experienced the cluster environment for a few Gyr

The observed [OII] trends at low-z seem to rule out the hypothesis that groups efficiently and universally quench star formation. Conversely, they show that the quenching is not limited to very massive clusters.

Not all “trends with environment” are necessarily due to environmental processes truncating star formation in recently accreted galaxies. Role of “primordial conditions”.