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

Abstract

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 μ 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  ∼ 1′. There is, however, one particularly bright source (2.3 mJy at 24 μ m; 106 mJy at 160 μ m), which corresponds to a background galaxy at z  = 0.61. The modest magnification factor (4.0×) implies that this galaxy is intrinsically IR luminous ( ). 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 α– H8) and forbidden emission from this clump ([O ii ] λ 3727, [O iii ]  λλ 4959,5007, [N ii ] λλ 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 mag, the star formation rate of this giant H ii region is ∼10 M ⊙ 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  ∼ 2 but is quite rare in the nearby universe.