ALMA observations of Ly α BLOB 1: halo substructure illuminated from within by Geach, J, Narayanan, D, Matsuda, Y, Hayes, M, Mas-Ribas, L, Dijkstra, M, Steidel, C, Chapman, S, Feldmann, R, Avison, A, Agertz, O, Ao, Y, Birkinshaw, M, Bremer, M, Clements, D, Dannerbauer, H, Farrah, D, Harrison, C, Kubo, M, Michałowski, M, Scott, D, Smith, D, Spaans, M, Simpson, J, Swinbank, A, Taniguchi, Y, Werf, P, Verma, A, Yamada, T