在局域宇宙中寻找扩展紫外盘星系
A Search for Extended Ultraviolet Disk (XUV-disk) Galaxies in the Local Universe
摘要：
我们已经开始了在本地宇宙中的扩展紫外盘（XUV盘）星系的搜索。在这里，我们比较了银河系近星系图集中包含的189个（D $<$ 40 Mpc）S 0-Sm星系的银河系紫外和可见光-近红外图像，并提出了第一个XUV盘星系目录。我们发现，XUV盘星系是令人惊讶的常见，但有不同的相对（UV/光学）的程度和形态。第1类天体（$\ga$ 20%的发生率）在外盘具有结构化的紫外线亮/光学暗发射特征，超出了传统的恒星形成阈值。2型XUV盘星系（$\sim$ 10%入射）在内部较老的恒星星族有效范围之外，存在一个异常大的紫外亮/光学低表面亮度（LSB）带，其蓝色$UV-K_s$位于该区域之外，但没有达到极端的银河系中心距离。如果发生在XUV盘的活动是偶发性的，那么今天的螺旋的更高比例可能会受到这种外盘恒星形成的影响。1型盘与所有类型的螺线都有联系，而2型XUV盘主要存在于晚型螺线中。2型XUV盘形成恒星的速度足够快，足以在下一个Gyr（假设SF速率恒定）中将其[目前较低的]恒星质量增加一倍。这两种类型的XUV盘星系都比一般的星系群更富含气体。微小的外部扰动可能会刺激XUV盘的入射，至少对于Type~1物体是这样。XUV盘是当前时期通过由内而外的盘形成而发展的最活跃的星系，并且可能构成星系人口的一部分，这些星系正在经历来自星系际介质或邻近物体的显著，持续的气体吸积。
英文摘要：
We have initiated a search for extended ultraviolet disk (XUV-disk) galaxies in the local universe. Herein, we compare GALEX UV and visible--NIR images of 189 nearby (D$<$40 Mpc) S0--Sm galaxies included in the GALEX Atlas of Nearby Galaxies and present the first catalogue of XUV-disk galaxies. We find that XUV-disk galaxies are surprisingly common but have varied relative (UV/optical) extent and morphology. Type~1 objects ($\ga$20% incidence) have structured, UV-bright/optically-faint emission features in the outer disk, beyond the traditional star formation threshold. Type~2 XUV-disk galaxies ($\sim$10% incidence) exhibit an exceptionally large, UV-bright/optically-low-surface-brightness (LSB) zone having blue $UV-K_s$ outside the effective extent of the inner, older stellar population, but not reaching extreme galactocentric distance. If the activity occuring in XUV-disks is episodic, a higher fraction of present-day spirals could be influenced by such outer disk star formation. Type~1 disks are associated with spirals of all types, whereas Type~2 XUV-disks are predominantly found in late-type spirals. Type~2 XUV-disks are forming stars quickly enough to double their [presently low] stellar mass in the next Gyr (assuming a constant SF rate). XUV-disk galaxies of both types are systematically more gas-rich than the general galaxy population. Minor external perturbation may stimulate XUV-disk incidence, at least for Type~1 objects. XUV-disks are the most actively evolving galaxies growing via inside-out disk formation in the current epoch, and may constitute a segment of the galaxy population experiencing significant, continued gas accretion from the intergalactic medium or neighboring objects.
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