CHORUS. I. Cosmic HydrOgen Reionization Unveiled with Subaru: Overview

Abstract

To determine the dominant sources for cosmic reionization, the evolution history of the global ionizing fraction, and the topology of the ionized regions, we have conducted a deep imaging survey using four narrow-band (NB) and one intermediate-band (IB) filters on the Subaru/Hyper Suprime-Cam (HSC), called Cosmic HydrOgen Reionization Unveiled with Subaru (CHORUS). The central wavelengths and full-widths-at-half-maximum of the CHORUS filters are, respectively, 386.2 nm and 5.5 nm for NB387, 526.0 nm and 7.9 nm for NB527, 717.1 nm and 11.1 nm for NB718, 946.2 nm and 33.0 nm for IB945, and 971.2 nm and 11.2 nm for NB973. This combination, including NB921 (921.5 nm and 13.5 nm) from the Subaru Strategic Program with HSC (HSC SSP), is carefully designed, as if they were playing a chorus, to observe multiple spectral features simultaneously, such as Lyman continuum, Lyα, C iv, and He ii for $z$ = 2–7. The observing field is the same as that of the deepest footprint of the HSC SSP in the COSMOS field and its effective area is about 1.6 deg2. We present an overview of the CHORUS project, which includes descriptions of the filter design philosophy, observations and data reduction, multiband photometric catalogs, assessments of the imaging quality, measurements of the number counts, and example use cases for the data. All the imaging data, photometric catalogs, masked pixel images, data of limiting magnitudes and point spread functions, results of completeness simulations, and source number counts are publicly available through the HSC SSP database.

SILVERRUSH. XI. Intensity Mapping for Lya Emission Extending over $100-1000$ comoving kpc around $z\sim2-7$ LAEs with Subaru HSC-SSP and CHORUS Data

“…Although their finding has shed light on the potential existence of Lyαemitting hydrogen gas beyond R vir around LAEs in the reionization epoch, it remains an open question whether LAEs host such extended structures even at lower redshifts (z < 5). In this paper, we exploit NB images offered in two Subaru/HSC surveys, the Cosmic Hy-drOgen Reionization Unveiled with Subaru (CHORUS; Inoue et al 2020) and the Subaru Strategic Program (HSC-SSP; Aihara et al 2019), which enable us to trace Lyα emission from LAEs across z = 2.2 − 6.6. Our goal is to systematically investigate diffuse Lyα emission extended beyond R vir around z = 2.2 − 6.6 LAEs, taking advantage of the intensity mapping technique and ultradeep images from the CHORUS and HSC-SSP projects.…”

CHORUS IV: Mapping the Spatially Inhomogeneous Cosmic Reionization with Subaru HSC

“…The IB945 images are taken through the CHORUS project (Inoue et al 2020). We have carried out deep imaging observation with IB945 in the COSMOS field, which is one of the UltraDeep layers of the HSC-SSP.…”

“…The limiting magnitude in each patch is calculated in the same way as Inoue et al (2020). We distribute ∼ 5000 apertures with 1 .5 diameter per patch avoiding the masked regions and detected sources and derive the limiting magnitude by fitting the flux distribution with a Gaussian function.…”

“…The detection completeness is defined as a number fraction of the mock galaxies that are successfully detected in the detection band images (Y and NB921 for LBGs and LAEs, respectively). We regard sources that are detected within 0 .5 from the positions of the mock galaxies and with a difference of 0.5 magnitude or less from the input magnitude as successfully detected objects (Inoue et al 2020). We apply the same selection to the mock galaxies as described in Sections 3.1 and 3.2 and calculate the selection completeness of our LAE and LBG samples.…”

“…In this paper, we use the imaging data taken by HSC Subaru Strategic Program (SSP; Aihara et al 2018a) 1 and Cosmic HydrOgen Reionization Unveiled with Subaru (CHORUS) project (Inoue et al 2020). This paper is constructed as follows.…”