Systematic survey of extended Lyα sources over z ∼ 3-5

Spatially extended Lyα sources that are faint and compact in continuum are candidates for extremely young (≲10⁷ yr) galaxies at high redshifts. We carried out a systematic survey for extended Lyα sources, using deep intermediate-band imaging data taken with the Suprime-Cam on the Subaru Telescope. Our survey covers a field of view of 33′ × 25× and a redshift range of 3.24 ≲ z ≲ 4.95, down to a Lyα flux of ∼1 × 10^-17 ergs cm^-2 s^-1. We identified 41 extended Lyα sources. The redshift distribution of these sources shows that this kind of object is common in the early universe over the surveyed redshift range. The identified objects have typical sizes of ∼10-15 kpc and luminosities of ∼10⁴² ergs s^-1. Follow-up spectroscopy made for 7 of the 41 objects showed that our sample suffers from little contamination. All 7 objects have large equivalent widths of Lyα emission line, all but one exceeding 240 Å in the rest frame. The large equivalent widths suggest that their extended Lyα emissions are unlikely to be due to normal starbursts, but possibly originate from very young galaxies. All 41 objects in our sample have much smaller Lyα luminosities than the two Lyα blobs (LABs) found at a z ≃ 3.1 protocluster, in spite of our much larger survey volume. This suggests that large and luminous extended Lyα objects like the two LABs are very rare and are clustered in overdense regions.