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.

Using stacks of Lyα images of 2128 Lyα emitters (LAEs) and 24 proto‐cluster UV‐selected galaxies (LBGs) at z = 3.1, we examine the surface brightness profiles of Lyα haloes around high‐z galaxies as a function of environment and UV luminosity. We find that the slopes of the Lyα radial profiles become flatter as the Mpc‐scale LAE surface density increases, but that they are almost independent of the central UV luminosity. The characteristic exponential scalelength of the Lyα haloes appears to be proportional to the square of the LAE surface density (r Ly α∝Σ LAE 2). Including the diffuse, extended Lyα haloes, the rest‐frame Lyα equivalent width of the LAEs in the densest regions approaches EW0 ∼ 200 Å, the maximum value expected for young (<107 yr) galaxies. This suggests that Lyα photons formed via shock compression by gas outflows or cooling radiation by gravitational gas inflows may partly contribute to the illumination of Lyα haloes; however, most of their Lyα luminosity can be explained by photoionization by or by scattering of Lyα photons produced from H ii regions in and around the central galaxies. Regardless of the source of Lyα photons, if the Lyα haloes trace the overall gaseous structure, following the dark matter distribution, it is not surprising that the Lyα spatial extent depends more strongly on the surrounding Mpc‐scale environment than on the activity of the central galaxies.

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.

We present the discovery of a candidate of giant radio‐quiet Lyα blob (RQLAB) in a large‐scale structure around a high‐redshift radio galaxy (HzRG) lying in a giant Lyα halo B3 J2330+3927 at redshift z= 3.087. We obtained narrow‐ and broad‐band imaging around B3 J2330+3927 with Subaru/Suprime‐Cam to search for Lyα emitters (LAEs) and absorbers (LAAs) at redshift z= 3.09 ± 0.03. We detected candidate 127 LAEs and 26 LAAs in the field of view of 31 × 24 arcmin2 (58 × 44 comoving Mpc). We found that B3 J2330+3927 is surrounded by a 130 kpc Lyα halo and a large‐scale (∼60 × 20 comoving Mpc) filamentary structure. The large‐scale structure contains one prominent local density peak with an overdensity of greater than 5, which is 8 arcmin (15 comoving Mpc) away from B3 J2330+3927. In this peak, we discovered a candidate 100 kpc RQLAB. The existence of both types of Lyα nebulae in the same large‐scale structure suggests that giant Lyα nebulae need special large‐scale environments to form. On smaller scales, however, the location of B3 J2330+3927 is not a significant local density peak in this structure, in contrast to the RQLAB. There are two possible interpretations of the difference of the local environments of these two Lyα nebulae. First, RQLAB may need a prominent (δ∼ 5) density peak of galaxies to form through intense starbursts due to frequent galaxy interactions/mergers and/or continuous gas accretion in an overdense environment. On the other hand, Lyα halo around HzRG may not always need a prominent density peak to form if the surrounding Lyα halo is mainly powered by its radio and active galactic nucleus activities. Alternatively, both RQLAB and Lyα halo around HzRG may need prominent density peaks to form but we could not completely trace the density of galaxies because we missed evolved and dusty galaxies in this survey.