A successful broadband survey for giant Lyα nebulae. I. Survey design and candidate selection

Giant Lyα nebulae (or Lyα "blobs") are likely sites of ongoing massive galaxy formation, but the rarity of these powerful sources has made it difficult to form a coherent picture of their properties, ionization mechanisms, and space density. Systematic narrowband Lyα nebula surveys are ongoing, but the small redshift range covered and the observational expense limit the comoving volume that can be probed by even the largest of these surveys and pose a significant problem when searching for such rare sources. We have developed a systematic search technique designed to find large Lyα nebulae at 2 ≲ z ≲ 3 within deep broadband imaging and have carried out a survey of the 9.4deg² NOAO Deep Wide-Field Survey Boötes field. With a total survey comoving volume of 10⁸h ^-3 ₇₀Mpc³, this is the largest volume survey for Lyα nebulae ever undertaken. In this first paper in the series, we present the details of the survey design and a systematically selected sample of 79 candidates, which includes one previously discovered Lyα nebula.