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

Walth G. L., Egami, E., Clement, B., Rawle, T. D., Rex, M., Richard, J., Pérez González, P., Boone, F., Dessauges Zavadsky, M., Portouw, J., Weiner, B., McGreer, I., Schneider, E. 2019. 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. Astrophysical Journal 877, 1, DOI: 10.3847/1538-4357/ab16d8

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.

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