We report the properties of the 35 robust candidates of Lyα blobs (LABs), which are larger than 16 arcsec 2 in isophotal area and brighter than 0.7 × 10 −16 ergs s −1 cm −2 , searched in and around the proto-cluster region at redshift z = 3.1 discovered by Steidel et al. in the SSA22 field, based on wide-field (31 ′ × 23 ′ ) and deep narrow-band (NB497; 4977/77) and broad-band (B,V , and R) images taken with the prime-focus camera on the Subaru telescope. The two previously known giant LABs are the most luminous and the largest ones in our survey volume of 1.3 × 10 5 Mpc 3 . We revealed the internal structures of the two giant LABs and discovered some bubble-like features, which suggest that intensive starburst and galactic superwind phenomena occurred in these objects in the past. The rest 33 LABs have isophotal area of ∼16-78 arcsec 2 and flux of 0.7-7 ×10 −16 ergs s −1 cm −2 . These 35 LABs show a continuous distribution of isophotal area and emission line flux. The distributions of average surface brightness and morphology are widespread from relatively compact high surface 1 Based on data collected at Subaru Telescope and in part obtained from data archive at Astronomical Data Analysis Center, which are operated by the National Astronomical Observatory of Japan.

We obtained a deep wide-field (32 0 ; 24 0 ) narrowband (k c ¼ 49778; Ák ¼ 778) image of a field including the protocluster at z ¼ 3:1 in the SSA22a field studied by Steidel et al. using the Subaru Telescope. The field we observed is about 10 times as large as that studied by Steidel et al. We detected 283 highly confident strong Ly emitter candidates at z $ 3:1 down to 25.8 AB mag with the observed equivalent width larger than 154 8. These strong Ly emitter candidates show a highly nonuniform distribution with the beltlike region of high surface density, which is found to extend over $60 Mpc in comoving scale. The average number density of the strong Ly emitter candidates in this high-density region is 3 times as high as that of a blank field. The probability of finding such a large-scale high-density peak is as small as 0.1% in the context of the CDM structure formation scenario, if we assume a linear bias parameter b $ 4. In addition to these strong Ly emitters, we also detected 49 Ly absorbers, which show significant deficit in the narrowband image. We further detected 74 extended emitters, which have significant fluxes over the areas of 18 arcsec 2 or more. Interestingly, both these absorbers and extended emitters show sky distributions very similar to that of the strong Ly emitters. This supports the reality of the large-scale structure at z ¼ 3:1 and suggests that galaxy formation preferentially occurs in the high-density region of strong Ly emitters.

We use observations from the Giant Metrewave Radio Telescope (GMRT) to measure the atomic hydrogen gas content of star‐forming galaxies at z= 0.24 (i.e. a look‐back time of ∼3 Gyr). The sample of galaxies studied were selected from Hα‐emitting field galaxies detected in a narrow‐band imaging survey with the Subaru Telescope. The Anglo‐Australian Telescope was used to obtain precise optical redshifts for these galaxies. We then co‐added the H i 21‐cm emission signal for all the galaxies within the GMRT spectral line data cube. From the co‐added signal of 121 galaxies, we measure an average atomic hydrogen gas mass of (2.26 ± 0.90) × 109  M⊙. We translate this H i signal into a cosmic density of neutral gas at z= 0.24 of Ωgas= (0.91 ± 0.42) × 10−3. This is the current highest redshift at which Ωgas has been constrained from 21‐cm emission and our value is consistent with that estimated from damped Lyα systems around this redshift. We also find that the correlations between the Hα luminosity and the radio continuum luminosity and between the star formation rate (SFR) and the H i gas content in star‐forming galaxies at z= 0.24 are consistent with the correlations found at z= 0. These two results suggest that the star formation mechanisms in field galaxies ∼3 Gyr ago were not substantially different from the present, even though the SFR is three times higher.

We present the results of a survey for Lyα emitters at z ≈ 5.7 based on optical narrow-band (λ c = 8150 Å and ∆λ = 120 Å), and broad-band (B, R C , I C , and z ′ ) observations of the field surrounding the high redshift quasar, SDSSp J104433.04−012522.2, on the 8.2 m Subaru Telescope with the Subaru Prime Focus Camera, Suprime-Cam. This survey covers a sky area of ≈ 720 arcmin 2 and a co-moving volume of ≃ 2 × 10 5 h −3 0.7 Mpc 3 . We have found 20 candidates of Lyα emitters at z ≈ 5.7 with ∆z ≈ 0.1. Two of them have been confirmed star-forming galaxies at z = 5.655 and z = 5.687 from our follow-up optical spectroscopy. We discuss star-formation properties of the 20 objects from a statistical point of view. Our survey leads to a new estimate of the star formation rate density at z ≈ 5.7, ∼ 1.2 × 10 −3 h 0.

The Subaru Deep Field (SDF) project is a program of Subaru Observatory to carry out a deep galaxy survey over a blank field as large as 34 ′ ×27 ′ . The program consists of very deep multi-band optical imaging, near infrared imaging for smaller portions of the field and follow-up optical spectroscopy. Major scientific goals of the project are to construct large samples of Lyman-break galaxies at z ≃ 4 − 5 and Lyman alpha emitters at z ≃ 5.7 and 6.6, and to make detailed studies these very high-redshift galaxy populations.In this paper, we describe the optical imaging observations and data reduction, presenting mosaicked images and object catalogs in seven bandpasses. The optical imaging was made through five broad-band filters, B, V , R, i ′ , z ′ , and two narrow-band filters, NB816 (λ c = 8150Å) and NB921 (λ c = 9196Å) with almost 10 hours long integrations for each band. The limiting magnitudes measured at 3σ on a 2 ′′ aperture are B = 28.45, V = 27.74, R = 27.80, i ′ = 27.43, z ′ = 26.62, NB816 = 26.63, and NB921 = 26.54 in the AB system. The object catalog constructed for each of the seven bands contains more than 10 5 objects. The galaxy number counts corrected for detection incompleteness and star count contribution are found to be consistent with previous results in the literature. The mosaicked images and catalogs of all the bands have been made open to the public on Oct. 1, 2004 on the SDF project website at http://soaps.naoj.org/sdf/.