We report the first evidence for high-mass star formation triggered by collisions of molecular clouds in M33. Using the Atacama Large Millimeter/submillimeter Array, we spatially resolved filamentary structures of giant molecular cloud 37 in M33 using $^{12}$CO($J$ = 2-1), $^{13}$CO($J$ = 2-1), and C$^{18}$O($J$ = 2-1) line emission at a spatial resolution of $\sim$2 pc. There are two individual molecular clouds with a systematic velocity difference of $\sim$6 km s$^{-1}$. Three continuum sources representing up to $\sim$10 high-mass stars with the spectral types of B0V-O7.5V are embedded within the densest parts of molecular clouds bright in the C$^{18}$O($J$ = 2-1) line emission. The two molecular clouds show a complementary spatial distribution with a spatial displacement of $\sim$6.2 pc, and show a V-shaped structure in the position-velocity diagram. These observational features traced by CO and its isotopes are consistent with those in high-mass star-forming regions created by cloud-cloud collisions in the Galactic and Magellanic Cloud HII regions. Our new finding in M33 indicates that the cloud-cloud collision is a promising process to trigger high-mass star formation in the Local Group.

中文翻译：

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M 33 中巨大分子云的 ALMA CO 观测：云-云碰撞引发大质量恒星形成的证据

我们报告了 M33 中分子云碰撞引发大质量恒星形成的第一个证据。使用 Atacama 大型毫米/亚毫米阵列，我们使用 $^{12}$CO($J$ = 2-1)、$^{13}$CO($J$) 空间解析了 M33 中巨型分子云 37 的丝状结构= 2-1) 和 C$^{18}$O($J$ = 2-1) 线发射，空间分辨率为 $\sim$2 pc。有两个单独的分子云，系统速度差异为 $\sim$6 km s$^{-1}$。三个连续谱源代表高达 $\sim$10 的光谱类型为 B0V-O7.5V 的大质量恒星，它们嵌入在 C$^{18}$O($J$ = 2 -1) 线发射。两个分子云显示出互补的空间分布，空间位移为 $\sim$6.2 pc，并在位置速度图中显示 V 形结构。这些由 CO 及其同位素追踪的观测特征与银河和麦哲伦星云 HII 区域的云-云碰撞产生的大质量恒星形成区域的特征一致。我们在 M33 中的新发现表明，云-云碰撞是触发本地群中大质量恒星形成的有希望的过程。