JCMT附近Galerkin遗产调查I.室女星系团螺旋星系团中的成星分子气体
The JCMT Nearby Galaxies Legacy Survey I. Star Forming Molecular Gas in Virgo Cluster Spiral Galaxies
摘要：
我们目前的大面积地图的CO J=3-2的排放得到的詹姆斯克拉克麦克斯韦望远镜的四个螺旋星系的室女星系团。我们将这些数据与已发表的CO J=1-0，24微米，和Halpha图像相结合，以测量CO线比，分子气体质量和瞬时气体耗尽时间。对于我们的样本中的三个星系（NGC 4254，NGC 4321和NGC 4569），我们得到的分子气体质量为7 E8 - 3E 9 Msun和盘平均瞬时气体耗尽时间为1.1-1.7 Gyr。我们认为，CO J=3-2线是一个更好的示踪剂的致密恒星形成的分子气体比CO J=1-0线，因为它显示了更好的相关性与恒星形成率的表面密度内和星系之间。NGC 4254似乎有更大的恒星形成效率（更短的气体耗尽时间），也许是因为它是第一次穿过室女星系团。NGC 4569的CO J=3-2/J=1-0线比显示出气体性质的大尺度梯度，这表明它与星团内介质的相互作用直接影响了星际介质的致密恒星形成部分。我们样本中的第四个星系，NGC 4579，尽管有明亮的24微米发射，但有微弱的CO J=3-2发射;然而，这个星系的大部分中心光度可能是由于中心活动星系核的存在。
英文摘要：
We present large-area maps of the CO J=3-2 emission obtained at the James Clerk Maxwell Telescope for four spiral galaxies in the Virgo Cluster. We combine these data with published CO J=1-0, 24 micron, and Halpha images to measure the CO line ratios, molecular gas masses, and instantaneous gas depletion times. For three galaxies in our sample (NGC 4254, NGC4321, and NGC 4569), we obtain molecular gas masses of 7E8-3E9 Msun and disk-averaged instantaneous gas depletion times of 1.1-1.7 Gyr. We argue that the CO J=3-2 line is a better tracer of the dense star forming molecular gas than the CO J=1-0 line, as it shows a better correlation with the star formation rate surface density both within and between galaxies. NGC 4254 appears to have a larger star formation efficiency(smaller gas depletion time), perhaps because it is on its first passage through the Virgo Cluster. NGC 4569 shows a large-scale gradient in the gas properties traced by the CO J=3-2/J=1-0 line ratio, which suggests that its interaction with the intracluster medium is affecting the dense star-forming portion of the interstellar medium directly. The fourth galaxy in our sample, NGC 4579, has weak CO J=3-2 emission despite having bright 24 micron emission; however, much of the central luminosity in this galaxy may be due to the presence of a central AGN.
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