Star formation and environment in clusters up to z  ~  2.2

INAF – Osservatorio Astronomico di Brera, via Brera 28, 20121 Milan Italy
e-mail: anand.raichoor@brera.inaf.it; stefano.andreon@brera.inaf.it

Received: 1 September 2011
Accepted: 24 October 2011

Abstract

Context. The dependence of galaxy star-formation activity on environment – especially in clusters – at high redshift is still poorly understood, as illustrated by the still limited number of z ≳ 1.4 clusters on the one hand, and by the still debated star formation-density relation at high redshift on the other hand.

Aims. The z_phot ~ 2.2 JKCS 041 cluster allows us to probe this environmental dependence of star formation activity at an unprecedented combination of redshifts and environments. Its study permits us to enhance our knowledge of high redshift clusters and to put strong leverage on observational constraints of galaxy evolution models.

Methods. We analyze deep u^∗g′r′i′z′JHK_s images from the CFHTLS/WIRDS surveys, which cover the JKCS 041 cluster field. We first estimate photometric redshifts based on multi-wavelength photometry. We then lead a careful analysis to test the presence of a Butcher-Oemler effect. We work on galaxies within 2 × r₂₀₀ with masses M ≥ 1.34 × 10¹¹ M_⊙, and use two comparison clusters at z = 0 and z = 1 of similar mass. We estimate the radial profiles of the fraction of blue galaxies, taking into account the star aging with decreasing redshift.

Results. After confirming the high redshift nature of JKCS 041, we find no evidence of a Butcher-Oemler effect between z ~ 2.2 and z ~ 0 for galaxies more massive than 1.34 × 10¹¹ M_⊙. In the cluster center, a change greater than Δf_blue/Δz = 0.16 between z ~ 0 and z ~ 2.2 would be easily detected. We also find that JKCS 041 shows a consistent and systematic increase in the fraction of star-forming galaxies with cluster-centric distance, hence with decreasing density, for both a M ≥ 1.34 × 10¹¹ M_⊙ selected sample and a lower mass sample. In particular, very few (less than 15%) star-forming galaxies are found within r₂₀₀/2 among high mass (M ≥ 1.34 × 10¹¹ M_⊙) galaxies.

Conclusions. Our results show that the present-day star formation-density relation is already in place at z ~ 2.2.