超巨星HI壳和NGC 6822中可能的伴星的起源
On the Origin of the Supergiant HI Shell and Putative Companion in NGC 6822
摘要：
我们提出了新的哈勃空间望远镜先进的相机调查成像的六个位置跨越5.8千秒差距的HI主轴的本地组dIrr NGC 6822，包括假定的同伴星系和大HI洞。深色星等图显示NGC 6822有超过50%的恒星是在最后~5 Gyr形成的。所有六个位置的恒星形成历史在最近的5亿年是相似的，包括低水平的恒星形成在整个这段时间和微弱的增加，在最近的5千万年的恒星形成率。假设该结构的寿命超过5亿年，恒星反馈可以产生巨大的HI洞;这种长寿的结构现在已经在多个系统中观察到，并且可能是具有固体旋转的星系中的常态。这颗伴星的古老恒星星族（红巨星和红团星）与NGC 6822扩展晕的恒星族一致;这与将这一结构解释为真正的相互作用伴星星系的观点相矛盾，也与通过相互作用将其与HI黑洞的形成联系起来的观点相矛盾。由于没有伴星系的恒星星族的证据，NGC 6822中扩展的HI结构最可能的解释是一个弯曲的盘倾斜到视线。
英文摘要：
We present new Hubble Space Telescope Advanced Camera for Surveys imaging of six positions spanning 5.8 kpc of the HI major axis of the Local Group dIrr NGC 6822, including both the putative companion galaxy and the large HI 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 HI 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 HI hole via an interaction. Since there is no evidence in the stellar population of a companion galaxy, the most likely explanation of the extended HI structure in NGC 6822 is a warped disk inclined to the line of sight.
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