Title: Environmental effects on the star formation activity in galaxies at z~1.2 in the COSMOS field
Author(s): Y. Ideue, T. Nagao, Y.Taniguchi, Y. Shioya, T. Saito, T. Murayama, and COSMOS team
Abstract: To understand the formation and evolution of galaxies strongly relies on investigations of
when and where stars formed in the history of the universe from high redshift to the present day.
A number of observational studies have investigated how the star formation rate density (SFRD)
varies as a function of redshift. Such studies brought us a global evolutionary picture of
the SFRD. However, we are still far from a complete understanding of the galaxy evolution since
the redshift evolution of such global SFRD gives us only the gaveragedh picture of the star formation history
in the universe.@It is thus essential to study the star formation in galaxies as a function of both the
redshift and the environment.
We investigate the relation between the star-formation activity in galaxies and environment at z~1.2 in
the COSMOS field, using the fraction of [OII] emitters and the local galaxy density. The fraction of [OII]
emitters appears to be almost constant over the surface density of galaxies between 0.2 and 10 Mpc^-2.
This trend is different from that seen in the local universe where the star-formation activity is weaker in
higher galaxy density regions. To understand this difference between z~1 and z~0, we study the fraction
of non-isolated galaxies as a function of local galaxy density. We find that the fraction of non-isolated
galaxies increases with increasing density. Our results suggest that the star formation in galaxies at z~1
is triggered by galaxy interaction and/or mergers.


Abstract should be within about 250 words.