A SYSTEMATIC SURVEY OF PROTOCLUSTERS AT z ∼ 3–6 IN THE CFHTLS DEEP FIELDS

Abstract

We present the discovery of three protoclusters at z ∼ 3-4 with spectroscopic confirmation in the Canada-FranceHawaii Telescope Legacy Survey Deep Fields. In these fields, we investigate the large-scale projected sky distribution of z ∼ 3-6 Lyman-break galaxies and identify 21 protocluster candidates from regions that are overdense at more than 4σ overdensity significance. Based on cosmological simulations, it is expected that more than 76% of these candidates will evolve into a galaxy cluster of at least a halo mass of 1014 M e at z = 0. We perform follow-up spectroscopy for eight of the candidates using Subaru/FOCAS, Keck II/DEIMOS, and Gemini-N/GMOS. In total we target 462 dropout candidates and obtain 138 spectroscopic redshifts. We confirm three real protoclusters at z = 3-4 with more than five members spectroscopically identified and find one to be an incidental overdense region by mere chance alignment. The other four candidate regions at z ∼ 5-6 require more spectroscopic follow-up in order to be conclusive. A z = 3.67 protocluster, which has 11 spectroscopically confirmed members, shows a remarkable core-like structure composed of a central small region (<0.5 physical Mpc) and an outskirts region (∼1.0 physical Mpc). The Lyα equivalent widths of members of the protocluster are significantly smaller than those of field galaxies at the same redshift, while there is no difference in the UV luminosity distributions. These results imply that some environmental effects start operating as early as at z ∼ 4 along with the growth of the protocluster structure. This study provides an important benchmark for our analysis of protoclusters in the upcoming Subaru/HSC imaging survey and its spectroscopic follow-up with the Subaru/PFS that will detect thousands of protoclusters up to z ∼ 6.

The Galaxy–Halo Connection in High-redshift Universe: Details and Evolution of Stellar-to-halo Mass Ratios of Lyman Break Galaxies on CFHTLS Deep Fields

“…Object detection and LBG sample selection were performed in the same manner as Toshikawa et al (2016). In this section, we present a brief outline of the photometry and the sample selection method.…”

Luminous quasars do not live in the most overdense regions of galaxies at z ∼ 4

“…Although there is a large scatter due to projection effects, surface overdensity significance is closely correlated with descendant halo mass at z = 0. Toshikawa et al (2016) showed that > 76% of > 4σ overdense regions of g-dropouts are expected to evolve into dark matter halos with masses of > 10 14 M⊙at z = 0 although there is no clear difference between < 4σ overdense regions and fields due to a large scatter. It should be noted that the success rate of this technique has already been established by our previous study of the ∼4 deg 2 of the CFHTLS Deep Fields, as the precursor of this HSC protocluster search, followed by Keck/DEIMOS and Subaru/FOCAS spectroscopy (Toshikawa et al 2016).…”

“…The expected 5σ limiting magnitudes for point sources are (g, r, i, z, y) = (26.5, 26.1, 25.9, 25.1, 24.4) mag measured in 2.0 arcsec apertures. We expect to obtain > 1400 protocluster candidates at z ∼ 4 by the end of the survey (Toshikawa et al 2017(Toshikawa et al , 2016. The HSC data (DR S16A Aihara et al 2017), which includes data taken before April 2016, has already produced an extremely wide field image of > 200 deg 2 with a median seeing of 0.…”

“…Red galaxies at intermediate redshifts and dwarf stars could satisfy our color selection criteria. The fraction of contamination from these objects in the g-dropout color selection is evaluated to be 25% at most at i < 25.0 (Ono et al 2017), 20% of which originates in photometric error (Toshikawa et al 2016). The overdensity significance should not be largely affected by the contamination.…”

Great Optically Luminous Dropout Research Using Subaru HSC (GOLDRUSH). I. UV luminosity functions at z ∼ 4–7 derived with the half-million dropouts on the 100 deg2 sky

“…We also check the spectroscopic catalogs shown in other studies (Saito et al 2008;Ouchi et al 2008;Willott et al 2010a;Curtis-Lake et al 2012;Masters et al 2012;Mallery et al 2012;Willott et al 2013;Le Fèvre et al 2013;Kashikawa et al 2015;Kriek et al 2015 4 ; Wang et al 2016;Toshikawa et al 2016;Momcheva et al 2016;Matsuoka et al 2016;Pâris et al 2017;Tasca et al 2017;Yang et al 2017;Masters et al 2017;Matsuoka et al 2017;Shibuya et al 2017b; R. Higuchi et al in preparation; see also Bañados et al 2016 whose redshifts are > 70 − 75% correct, i.e., sources with redshift reliability flags of 2, 3, 4, 9, 12, 13, 14, and 19. Here we focus on sources with spectroscopic redshifts zspec > 3 in these catalogs.…”