Environmental effects on star formation activity at z ∼ 0.9 in the cosmos field

M. Kajisawa, Y. Shioya, Y. Aida, Y. Ideue, Y. Taniguchi, T. Nagao, T. Murayama, K. Matsubayashi, L. Riguccini

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3 Citations (Scopus)


We investigated the fraction of [O II] emitters in galaxies at z ∼ 0.9 as a function of the local galaxy density in the Hubble Space Telescope (HST) COSMOS 2 deg2 field. [O II] emitters are selected by the narrowband excess technique with the NB711-band imaging data taken with Suprime-Cam on the Subaru telescope. We carefully selected 614 photo-z-selected galaxies with M U3500 < -19.31 at z = 0.901 - 0.920, which includes 195 [O II] emitters, to directly compare the results with our previous study at z ∼ 1.2. We found that the fraction is almost constant at 0.3 Mpc-2 < Σ10th < 10 Mpc-2. We also checked the fraction of galaxies with blue rest-frame colors of NUV-R < 2 in our photo-z-selected sample, and found that the fraction of blue galaxies does not significantly depend on the local density. On the other hand, the semi-analytic model of galaxy formation predicted that the fraction of star-forming galaxies at z ∼ 0.9 decreases with increasing projected galaxy density even if the effects of the projection and the photo-z error in our analysis were taken into account. The fraction of [O II] emitters decreases from ∼60% at z ∼ 1.2 to ∼30% at z ∼ 0.9 independent of galaxy environment. The decrease of the [O II] emitter fraction could be explained mainly by the rapid decrease of star formation activity in the universe from z ∼ 1.2 to z ∼ 0.9.

Original languageEnglish
Article number51
JournalAstrophysical Journal
Issue number1
Publication statusPublished - 2013 May 1


  • galaxies: evolution
  • galaxies: high-redshift
  • galaxies: star formation


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