Systematic Survey of Extended Lyman-alpha Sources over z~3-5

Spatially extended Ly-alpha sources which are faint and compact in coninuum are candidates for extremely young galaxies (age of ~<10e+7 yrs) at high redshifts. We carried out a systematic survey for extended Ly-alpha 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 Ly-alpha flux of ~1e-17 ergs/cm^2/s. We identified 41 extended Ly-alpha sources. The redshift distribution of these sources shows that this kind of objects are common in the early universe over the surveyed redshift range. The identified objects have typical sizes of \~10-15 kpc and luminosities of ~10^42 ergs/s. 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 Ly-alpha emission line, all but one exceeding 240A in the rest frame. The large equivalent widths suggest that their extended Ly-alpha emissions are unlikely to be due to normal starbursts, but possibly originated from very young galaxies. All 41 objects in our sample have much smaller Ly-alpha luminosities than the two Ly-alpha Blobs (LABs) found by Steidel et al. (2000) in spite of our much larger survey volume. This suggests that large and luminous extended Ly-alpha objects like the two LABs are very rare and are clustered in overdense regions.