The hybrid and wide-field cluster survey with HSC-SSP data: Star-formation history in the clusters at z~1


Moegi Yamamoto

We are now proceeding a project using HSC-SSP wide and deep survey data, named HSC-HSC (Hybrid Search for Clusters with HSC), in which we apply our new hybrid technique to search for galaxy clusters at z~0.5-1.7 with as little bias as possible on galaxy populations. We combine the following two techniques:(1) "Red sequence survey"; a conventional technique based on broad-band photometries to search for color- magnitude relation. This is therefore sensitive to passively evolving galaxies with little or no star formation.(2) "Blue cloud survey"; using a series of narrow-band filters available on HST to search for clustering of line emitting galaxies. This is therefore sensitive to star forming galaxies.By combining these two techniques, we can discover both old and young clusters and construct more representative sample of galaxy clusters covering the wide range in past star formation histories. In this program, we will mainly report the first result of “Red sequence survey”. We have found 21 cluster/group candidates at z~0.8-1.1 using HSC Ultra- deep survey data in the COSMOS field(1 HSC FoV). Using the stacking analysis and the field subtraction technique, we obtained the fraction of the blue galaxies in the cluster core(fb=0.25±0.07 at z~0.91). We will investigate the properties of galaxies such as the blue fraction in wider field and redshift range statistically. Also, we found ~50 cluster/group candidates at z~0.8-1.3 in the COSMOS and SXDS fields(2 HSC FoV). In addition, we have started the “blue cloud survey” and found somefollowing two techniques:(1) "Red sequence survey"; a conventional technique based on broad-band photometries to search for color- magnitude relation. This is therefore sensitive to passively evolving galaxies with little or no star formation.(2) "Blue cloud survey"; using a series of narrow-band filters available on HST to search for clustering of line emitting galaxies. This is therefore sensitive to star forming galaxies.By combining these two techniques, we can discover both old and young clusters and construct more representative sample of galaxy clusters covering the wide range in past star formation histories. In this program, we will mainly report the first result of “Red sequence survey”. We have found 21 cluster/group candidates at z~0.8-1.1 using HSC Ultra- deep survey data in the COSMOS field(1 HSC FoV). Using the stacking analysis and the field subtraction technique, we obtained the fraction of the blue galaxies in the cluster core(fb=0.25±0.07 at z~0.91). We will investigate the properties of galaxies such as the blue fraction in wider field and redshift range statistically. Also, we found ~50 cluster/group candidates at z~0.8-1.3 in the COSMOS and SXDS fields(2 HSC FoV). In addition, we have started the “blue cloud survey” and found some overdensity region of [OII] emitters at z~1.2. We will briefly touch on this first result too.