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 report the discovery of a large-scale coherent filamentary structure of Lyα emitters in a redshift space at z = 3.1. We carried out spectroscopic observations to map the three dimensional structure of the belt-like feature of the Lyα emitters discovered by our previous narrow-band imaging observations centered on the protocluster at z = 3.1. The feature was found to consist of at least three physical filaments connecting with each other. The result is in qualitative agreement with the prediction of the 'biased' galaxy-formation theories that galaxies preferentially formed in large-scale filamentary or sheet-like mass overdensities in the early Universe. We also found that the two known giant Lyα emission-line nebulae showing high star-formation activities are located near the intersection of these filaments, which presumably evolves into a massive cluster of galaxies in 1 Based on data collected at Subaru Telescope which is operated by the National Astronomical Observatory of Japan.-2the local Universe. This may suggest that massive galaxy formation occurs at the characteristic place in the surrounding large-scale structure at high redshift.

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.