标题： 猎户座A的C$^{18}$O核心质量函数：单天线观测 显示英文标题

标题： The C$^{18}$O core mass function toward Orion A: Single-dish observations

摘要： 我们利用 Nobeyama 射电天文台 (NRO) 45 米望远镜，在猎户座A巨分子云的 C$^{18}$O ($J$=1--0) 辐射线开展了对致密核的无偏巡天。该地图的有效角分辨率为 26"，对应于距离 414 pc 时 $\sim$ 0.05 pc。 利用赫歇尔-普朗克卫星的H$_2$柱密度图，我们计算了C$^{18}$O 的分数丰度，发现其在整个柱密度范围（$\lesssim$ 5 $\times$ 10$^{22}$ cm$^{-3}$）内大致保持恒定，尽管我们发现在较高的柱密度下存在C$^{18}$O 富集的趋势。 因此，C$^{18}$O 强度可以相当好地跟踪云的结构。 猎户座A 中的平均 C$^{18}$O 丰度估计为 5.7$\times$10$^{-7}$，这大约是标准值的三倍。 我们使用 astrodendro 识别了 746 个 C$^{18}$O 核，并将其中 709 个分类为无星核。 我们通过分解 Herschel-Planck 尘埃柱密度，利用视线分量的 C$^{18}$O 积分强度的相对比例来计算核的质量。 应用此方法，我们试图去除背景发射（即核外环境气体）的贡献。 然后，我们推导出无星核的质量函数，并发现它类似于恒星初始质量函数（IMF）。 对于无恒星核心的CMF，$dN/dM$，用幂律关系$M^\alpha$拟合，幂指数为$\alpha = -$2.25$\pm$0.16 在高质量斜率处（$\gtrsim$ 0.44 $M_\odot$）。 我们还发现，每个核心的质量与视线方向上积分的总质量之比显著较大。 因此，在之前的研究中，从尘埃图像推导的核心质量至少被高估了几倍。 相应地，这类先前的研究可能会低估单个核心的恒星形成效率。 显示英文摘要

摘要： We have performed an unbiased dense core survey toward the Orion A Giant Molecular Cloud in the C$^{18}$O ($J$=1--0) emission line taken with the Nobeyama Radio Observatory (NRO) 45-m telescope. The effective angular resolution of the map is 26", which corresponds to $\sim$ 0.05 pc at a distance of 414 pc. By using the Herschel-Planck H$_2$ column density map, we calculate the C$^{18}$O fractional abundance and find that it is roughly constant over the column density range of $\lesssim$ 5 $\times$ 10$^{22}$ cm$^{-3}$, although a trend of C$^{18}$O depletion is determined toward higher column density. Therefore, C$^{18}$O intensity can follow the cloud structure reasonably well. The mean C$^{18}$O abundance in Orion A is estimated to be 5.7$\times$10$^{-7}$, which is about 3 times larger than the fiducial value. We identified 746 C$^{18}$O cores with astrodendro and classified 709 cores as starless cores. We compute the core masses by decomposing the Herschel-Planck dust column density using the relative proportions of the C$^{18}$O integrated intensities of line-of-sight components. Applying this procedure, we attempt to remove the contribution of the background emission, i.e., the ambient gas outside the cores. Then, we derived mass function for starless cores and found that it resembles the stellar initial mass function (IMF). The CMF for starless cores, $dN/dM$, is fitted with a power-law relation of $M^\alpha$ with a power index of $\alpha = -$2.25$\pm$ 0.16 at the high-mass slope ($\gtrsim$ 0.44 $M_\odot$). We also found that the ratio of each core mass to the total mass integrated along the line of sight is significantly large. Therefore, in the previous studies, the core masses derived from the dust image are likely to be overestimated at least by a factor of a few. Accordingly, such previous studies may underestimate the star formation efficiency of individual cores.