Knowing the amount of ionizing photons from young star-forming galaxies is of particular importance to understanding the reionization process. Here we report initial results of Subaru/Suprime-Cam deep imaging observation of the SSA22 proto-cluster region at z = 3.09, using a special narrow-band filter to optimally trace ionizing radiation from galaxies at z ∼ 3. The unique wide field-of-view of Suprime-Cam enabled us to search for ionizing photons from 198 galaxies (73 Lyman break galaxies (LBGs) and 125 Ly-α emitters (LAEs)) with spectroscopically measured redshifts z ≃ 3.1. We detected ionizing radiation from 7 LBGs, as well as from 10 LAE candidates. Some of the detected galaxies show significant spatial offsets of ionizing radiation from non-ionizing UV emission. For some LBGs the observed non-ionizing UV to Lyman continuum flux density ratios are smaller than values expected from population synthesis models with a standard Salpeter initial mass function (IMF) with moderate dust attenuation (which is suggested from the observed UV slopes), even if we assume very transparent IGM along the sightlines of these objects. This implies an intrinsically bluer spectral energy distribution, e.g, that produced by a top-heavy IMF, for these LBGs. The observed flux desity ratios of non-ionizing UV to ionizing radiation of 7 detected LBGs range from 2.4 to 23.8 and the median is 6.6. The observed flux density ratios of the detected LAEs are even smaller than LBGs, if they are truly at z ≃ 3.1. We find that the median value of the flux density ratio for the deteced LBGs suggest that their escape fractions is likely to be higher than 4%, if the Lyman continuum escape is isotropic. The results imply that some of the LBGs in the proto-cluster at z ∼ 3 have the escape fraction significantly higher than that of galaxies (in a general field) at z ∼ 1 studied previously.

We present results of a survey for giant Lyα blobs (LABs) at z= 3 with Subaru/Suprime‐Cam. We obtained Lyα imaging at z= 3.09 ± 0.03 around the SSA22 protocluster and in several blank fields. The total survey area is 2.1 deg2, corresponding to a comoving volume of 1.6 × 106 Mpc3. Using a uniform detection threshold of 1.4 × 10−18 erg s−1 cm−2 arcsec−2 for the Lyα images, we construct a sample of 14 LAB candidates with major‐axis diameters larger than 100 kpc, including five previously known blobs and two known quasars. This survey triples the number of known LABs over 100 kpc. The giant LAB sample shows a possible ‘morphology–density relation’: filamentary LABs reside in average density environments as derived from compact Lyα emitters, while circular LABs reside in both average density and overdense environments. Although it is hard to examine the formation mechanisms of LABs only from the Lyα morphologies, more filamentary LABs may relate to cold gas accretion from the surrounding intergalactic medium (IGM) and more circular LABs may relate to large‐scale gas outflows, which are driven by intense starbursts and/or by active galactic nucleus activities. Our survey highlights the potential usefulness of giant LABs to investigate the interactions between galaxies and the surrounding IGM from the field to overdense environments at high redshift.

We present the results of the extensive narrowband survey of Lyα emission-line objects at z = 3.1 in the 1.38 deg 2 area surrounding the high-density region of star-forming galaxies at z = 3.09 in the SSA22 field, as well as in the 1.04 deg 2 area of the three separated general blank fields. In total, of 2161 Lyα emitters, there are 1394 in the SSA22 fields and 767 in the general fields detected at the narrowband AB magnitude limit of 25.73, which corresponds to the line flux of ≈1.8 × 10 −17 erg s −1 cm −2 or the luminosity of ≈1.5 × 10 42 erg s −1 at z = 3.1, above the observed equivalent-width threshold, ≈190 Å. The average surface number density of the emitters at z = 3.1 in the general fields above the thresholds is 0.20 ± 0.01 arcmin −2 . The SSA22 high-density region at z = 3.09, whose peak local density is six times that of the average, is found to be the most prominent outstanding structure in the whole surveyed area and is firmly identified as a robust "protocluster." We also compared the overdensity of the 100 arcmin 2 and 700 arcmin 2 areas which contain the protocluster with the expected fluctuation of the dark matter as well as those of the model galaxies in cosmological simulations. We found that the peak height values of the overdensity are 8-10 and 3-4 times the expected standard deviations for the counts of Lyα emitters at z = 3.1 in the corresponding volume, respectively. We conclude that the structure at z = 3.09 in the SSA22 field is a very significant and rare density peak up to the scale of ≈60 Mpc.

We present the results of the observations of the Lyα line profiles of 91 emission-line galaxies at z = 3.1 with the spectral resolution of λ/δλ(FWHM) ≈ 1700, or 180 km s −1 . A significant fraction, ∼ 50% of the observed objects show the characteristic double peaks in their Lyα profile. The red peak is much stronger than the blue one for most of the cases. The red peaks themselves also show weak but significant asymmetry and their widths are correlated with the velocity separation of the red and the blue peaks, which implies that the peaks are not isolated multiple components with different velocities but the parts of the single line which is modified by the absorption and/or scattering by the associated neutral hydrogen gas. The characteristic profile can be naturally explained by the scattering in the expanding shell of neutral hydrogen surrounding the Lyα emitting region while the attenuation by the inter-galactic medium should also be considered. Our results suggest that the star-formation in these Lyα emitters are dominated by the young burst-like events which produce the intrinsic Lyα emission as well as the gas outflow.

Deep narrow-band (NB359) imaging with Subaru telescope by Iwata et al. has detected a surprisingly strong Lyman continuum (LyC; ∼900 Å in the rest frame) from some Lyman α emitters (LAEs) at z = 3.1. However, the possibility of a redshift misidentification by the previous spectroscopic studies due to a narrow wavelength coverage cannot be rejected. Here we present the results of a new technique, the deep spectroscopy, in which we covered 4000-7000 Å with VLT/VIMOS and Subaru/FOCAS for the eight LAEs detected in NB359. All the eight objects have only one detectable emission line around 4970 Å , which is most likely to be Lyα at z = 3.1, and thus, the objects are certainly LAEs at the redshift. However, five of them show a ∼0.8 arcsec spatial offset between the Lyα emission and the source detected in NB359. No indications of the redshifts of the NB359 sources are found although it is statistically difficult that all the five LAEs have a foreground object accounting for the NB359 flux. The rest three LAEs show no significant offset from the NB359 position. Therefore, we conclude that they are truly LyC-emitting LAEs at z = 3.1. We also examine the stellar population which simultaneously accounts for the strength of the LyC and the spectral slope of non-ionizing ultraviolet of the LAEs. We consider the latest statistics of Lyman limit systems to estimate the LyC optical depth in the intergalactic medium (IGM) and an additional contribution of the bound-free LyC from photoionized nebulae to the LyC emissivity. As a result, we find that stellar populations with metallicity Z ≥ 1/50 Z can explain the observed LyC strength only with a very top-heavy initial mass function (IMF; m ∼ 50 M ). However, the critical metallicity for such an IMF is expected to be much lower. A very young (∼1 Myr) and massive (∼100 M ) extremely metal-poor (Z ≤ 5 × 10 −4 Z ) or metal-free (so-called Population III) stellar population can reproduce the observed LyC strength. The required mass fraction of such 'primordial' stellar population is ∼1-10 per cent in total stellar mass of the LAEs. We also present a possible evolutionary scenario of galaxies emitting strong LyC and implications of the primordial stars at z ∼ 3 for the metal enrichment in the intergalactic medium and for the ionizing background and reionization.