恒星反馈是否会产生HI孔洞？Holmberg II的HST/VLA研究
Does Stellar Feedback Create HI Holes? An HST/VLA Study of Holmberg II
摘要：
利用深HST/ACS F555 W和F814 W测光方法对M81群矮星系不规则星系Ho II中的恒星进行测光，研究中性ISM（HI）中的黑洞是由恒星反馈产生的假说。从深测光出发，我们构造了色星等图（CMD），测量了两个独立的黑洞目录中HI洞所含恒星的恒星形成历史（SFH），并选择了控制场，类似大小的区域跨越HI柱密度的范围。将最近的SFH转换成恒星反馈能量，我们发现已经产生了足够的能量来创造所有的洞。然而，所需的能量并不总是产生在一个时间尺度，这是小于估计的运动年龄的孔。结合CMD、最近的SFH和年轻恒星的位置，我们发现HI洞内的恒星星族并不是先前所认为的相干的、单年龄的星团，而是分布在每个洞内的多年龄的恒星族。从模拟和观察到的综合星等的比较，和HI洞内的恒星的位置和能量，我们提出了一个潜在的新模型：一个可行的机制，用于创建所观察到的HI洞在Ho II是恒星的反馈，从多个世代的SF分散在几十或几百万年，因此，HI洞的年龄的概念本质上是模糊的。我们进一步发现，\halpha和24微米的排放，最近的恒星形成的示踪剂，不相关的HI孔的位置。然而，紫外线辐射，跟踪恒星形成大约在过去的1亿年，显示出更好的相关性与HI洞的位置。
英文摘要：
We use deep HST/ACS F555W and F814W photometry of resolved stars in the M81 Group dwarf irregular galaxy Ho II to study the hypothesis that the holes identified in the neutral ISM (HI) are created by stellar feedback. From the deep photometry, we construct color-magnitude diagrams (CMDs) and measure the star formation histories (SFHs) for stars contained in HI holes from two independent holes catalogs, as well as select control fields, i.e., similar sized regions that span a range of HI column densities. Converting the recent SFHs into stellar feedback energies, we find that enough energy has been generated to have created all holes. However, the required energy is not always produced over a time scale that is less than the estimated kinematic age of the hole. The combination of the CMDs, recent SFHs, and locations of young stars shows that the stellar populations inside HI holes are not coherent, single-aged, stellar clusters, as previously suggested, but rather multi-age populations distributed across each hole. From a comparison of the modeled and observed integrated magnitudes, and the locations and energetics of stars inside of HI holes, we propose a potential new model: a viable mechanism for creating the observed HI holes in Ho II is stellar feedback from multiple generations of SF spread out over tens or hundreds of Myr, and thus, the concept of an age for an HI hole is intrinsically ambiguous. We further find that \halpha and 24 micron emission, tracers of the most recent star formation, do not correlate well with the positions of the HI holes. However, UV emission, which traces star formation over roughly the last 100 Myr, shows a much better correlation with the locations of the HI holes.
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