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On the Origin of the Supergiant H I Shell and Putative Companion in Ngc 6822


Cannon, JM and O'Leary, EM and Weisz, DR and Skillman, ED and Dolphin, AE and Bigiel, F and Cole, AA and de Blok, WJG and Walter, F, On the Origin of the Supergiant H I Shell and Putative Companion in Ngc 6822, Astrophysical Journal, 747, (2) Article 122. ISSN 0004-637X (2012) [Refereed Article]

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Copyright 2012 The American Astronomical Society

DOI: doi:10.1088/0004-637X/747/2/122


We present new Hubble Space Telescope Advanced Camera for Surveys imaging of six positions spanning 5.8 kpc of the H I major axis of the Local Group dIrr NGC 6822, including both the putative companion galaxy and the large H I hole. The resulting deep color-magnitude diagrams show that NGC 6822 has formed >50% of its stars in the last ~5 Gyr. The star formation histories of all six positions are similar over the most recent 500 Myr, including low-level star formation throughout this interval and a weak increase in star formation rate during the most recent 50 Myr. Stellar feedback can create the giant H I hole, assuming that the lifetime of the structure is longer than 500 Myr; such long-lived structures have now been observed in multiple systems and may be the norm in galaxies with solid-body rotation. The old stellar populations (red giants and red clump stars) of the putative companion are consistent with those of the extended halo of NGC 6822; this argues against the interpretation of this structure as a bona fide interacting companion galaxy and against its being linked to the formation of the H I hole via an interaction. Since there is no evidence in the stellar population of a companion galaxy, the most likely explanation of the extended H I structure in NGC 6822 is a warped disk inclined to the line of sight.

Item Details

Item Type:Refereed Article
Keywords:galaxies: dwarf; galaxies: evolution; galaxies: individual (NGC 6822); galaxies: irregular
Research Division:Physical Sciences
Research Group:Astronomical sciences
Research Field:Cosmology and extragalactic astronomy
Objective Division:Expanding Knowledge
Objective Group:Expanding knowledge
Objective Field:Expanding knowledge in the physical sciences
UTAS Author:Cole, AA (Associate Professor Andrew Cole)
ID Code:78624
Year Published:2012
Web of Science® Times Cited:17
Deposited By:Mathematics and Physics
Deposited On:2012-07-10
Last Modified:2015-02-10

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