Infrared Galaxies In The Field Of The Massive Cluster Abell S1063: Discovery Of A Luminous Kiloparsec-Sized H Ii Region In A Gravitationally Lensed Infrared-Luminous Galaxy At Z=0.6

Using the Spitzer Space Telescope and Herschel Space Observatory, we have conducted a survey of IR galaxies in the field of the galaxy cluster AS1063 at z = 0.347, which is one of the most massive clusters known and a target of the Hubble Space Telescope (HST) Cluster Lensing and Supernova Survey with Hubble and the Frontier Field surveys. The Spitzer/MIPS 24 mu m and Herschel/PACS and SPIRE images revealed that the core of AS1063 is surprisingly devoid of IR sources, showing only a few detectable sources within the central r similar to 1'. There is, however, one particularly bright source (2.3 mJy at 24 mu m; 106 mJy at 160 mu m), which corresponds to a background galaxy at z = 0.61. The modest magnification factor (4.0x) implies that this galaxy is intrinsically IR luminous (L-IR = 3.1 x 10(11 )L(circle dot)). What is particularly interesting about this galaxy is that HST optical/near-IR images show a remarkably bright and large (1 kpc) clump at one edge of the disk. Our follow-up optical/near-IR spectroscopy shows Balmer (H alpha-H8) and forbidden emission from this clump ([O II] lambda 3727, [O III] lambda lambda 4959,5007, [N II] lambda lambda 6548,6583), indicating that it is an H II region. The H II region appears to have formed in situ, as kinematically it is part of a rotating disk, and there is no evidence of nearby interacting galaxies. With an extinction correction of A(v) = 1.5 mag, the star formation rate of this giant H II region is similar to 10 M-circle dot yr(-1), which is exceptionally large, even for high-redshift H II regions. Such a large and luminous H II region is often seen at z similar to 2 but is quite rare in the nearby universe.