一个具有异常遥远恒星形成的气体群
A Gaseous Group with Unusual Remote Star Formation
摘要：
我们对旋涡星系ESO 481-G017进行了VLA 21 cm观测，以确定距离星系中心43 kpc、约800 km s ^-1的HII区（投影）所追踪的遥远恒星形成的性质。ESO 481-G017被发现有一个质量为1.2x10^10 Msun的120 kpc HI盘，UV GALEX图像显示螺旋臂延伸到气体盘中。在距离ESO 481-G017约200 kpc处探测到两个HI质量接近10^8 Msun的矮星系，在遥远的HII区域的位置和速度附近发现了一个质量为6x10^7 Msun的HI云。HII区域在空间上与HI云有些偏移，与ESO 481-G017或矮星系没有联系。我们考虑了几种情况下的云和HII区域的起源，并发现最有可能是一个矮星系，正在经历冲压压力剥离。星云的HI质量和HII区的H α光度（10^38.1 erg s ^-1）与矮星系的性质一致，剥离可以触发恒星的形成，也可以将气体推离恒星。
英文摘要：
We present VLA 21-cm observations of the spiral galaxy ESO 481-G017 to determine the nature of remote star formation traced by an HII region found 43 kpc and ~800 km s^-1 from the galaxy center (in projection). ESO 481-G017 is found to have a 120 kpc HI disk with a mass of 1.2x10^10 Msun and UV GALEX images reveal spiral arms extending into the gaseous disk. Two dwarf galaxies with HI masses close to 10^8 Msun are detected at distances of ~200 kpc from ESO 481-G017 and a HI cloud with a mass of 6x10^7 Msun is found near the position and velocity of the remote HII region. The HII region is somewhat offset from the HI cloud spatially and there is no link to ESO 481-G017 or the dwarf galaxies. We consider several scenarios for the origin of the cloud and HII region and find the most likely is a dwarf galaxy that is undergoing ram pressure stripping. The HI mass of the cloud and Halpha luminosity of the HII region (10^38.1 erg s^-1) are consistent with dwarf galaxy properties, and the stripping can trigger the star formation as well as push the gas away from the stars.
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