Identifying protoclusters in distant universe

Abstract

Properties of galaxies, such as color, age, and star formation activity, appear to be associated with the environment in which they are immersed. To investigate how the environment-galaxy relation is established, we study protoclusters, which are numerically dense environments of galaxies in the early Universe, and which give rise to galaxy clusters today. In this work, we use submillimeter galaxies (SMGs)-which are very dusty and distant galaxies, with their copious infrared emission redshifted to the submillimeter wavelengths-as lampposts to trace potential sites of protocluster regions. We undertook deep observations of the environment of SMGs with well-established spectroscopic redshifts in the range of z ≃ 1-5. We made a combination of deep imaging and spectroscopic observations to identify Lyman-alpha emitters (LAEs) as a means to assess the more typical star-forming galaxies in these regions. We identified more than 300 LAE candidates in four potential protocluster regions. Of these, 200 have already been spectroscopically confirmed to be at the SMG redshifts. This is consistent with them being part of the same structure. By probing the redshift range z ≃ 1-5, which corresponds to ≥4 Giga years, we seek insights on the evolution of protoclusters over this time interval.