Identifying and Characterizing Lyman-Alpha Blobs at z = 4.9*

The surrounding gas of galaxies, known as the circumgalactic medium (CGM) and intergalactic medium (IGM), is insightful to learn about galaxy evolution. Lyman-alpha blobs (LABs), extended objects in Lyman-alpha emission, are useful laboratories for understanding the CGM/IGM and their link to galaxy evolution. Previous studies have suggested the two main factors for producing LABs -- galaxy overdensities and the active galactic nucleus (AGN) -- given their associations with them. However, that picture does not fully constrain due to their rarity. We aim to understand the cause of LABs using larger samples. Our NB718 narrow-band and broadband images with unprecedented wide field-of-views (1.8 deg²) taken by the Hyper Suprime-Cam/Subaru telescope allowed us to find 18 LABs at z = 4.9, including 17 newly identified. Our overdensity analysis shows that not all LABs are in overdense regions. We also do not find any associations of AGNs to our LABs. Those results different from the literature may indicate the need for other factors to produce LABs or the lack of observational probes of the current data. Further observations will need to resolve the cause in more detail.