arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 1706.04871astro-ph.GA
收藏

小麦哲伦云恒星形成早期阶段N83C的ALMA观测

ALMA observations of N83C in the early stage of star formation in the Small Magellanic Cloud

Kazuyuki Muraoka, Aya Homma, Toshikazu Onishi, Kazuki Tokuda, Ryohei Harada, Yuuki Morioka, Sarolta Zahorecz, Kazuya Saigo, Akiko Kawamura, Norikazu Mizuno, Tet… 展开作者

Kazuyuki Muraoka, Aya Homma, Toshikazu Onishi, Kazuki Tokuda, Ryohei Harada, Yuuki Morioka, Sarolta Zahorecz, Kazuya Saigo, Akiko Kawamura, Norikazu Mizuno, Tetsuhiro Minamidani, EriK Muller, Yasuo Fukui, Margaret Meixner, Remy Indebetouw, Marta Sewiło, Alberto D. Bolatto

摘要:

我们在小麦哲伦云(SMC)中的活跃恒星形成区N83 C(其金属丰度为银河系(MW)的1/5)的$^{12}$ CO($J=2-1$)、$^{13}$ CO($J=2-1$)、C $^{18}$ O($J=2-1$)、$^{12}$ CO($J=3-2$)、$^{13}$ CO($J=3-2$)和CS($J=7-6$)线上进行了阿塔卡马大型毫米/亚毫米阵列(ALMA)观测。ALMA观测首次揭示了$^{12}$ CO($J=2-1$)和$^{13}$ CO($J=2-1$)发射的亚pc尺度分子结构。我们发现了与$Spitzer$空间望远镜识别的年轻恒星物体(YSO)相关的强CO峰,并且还发现整体分子气体沿着邻近的HII区域的边缘分布。根据从$J=2-1$ CO($^{12}$)发射估算的维里质量,我们推导出与YSO相关的分子云中的气体密度为$\sim 10^4$ cm $^{-3}$。这种高的气体密度可能是由于在SMC中的低金属含量(相应的小灰尘含量)环境下的HII区域的影响;来自HII区域的远紫外辐射可以容易地穿透并光解离分子云中的$^{12}$ CO分子的外层,因此即使在$^{12}$ CO排放中也只能观察到分子云的最内部部分。基于维里质量和CO光度,我们得到了N83 C中$7.5 \times 10^{20}$ cm $^{-2}$(K km s $^{-1}$)$^{-1}$的CO到H的$_2$转换因子$X_{\rm CO}$,它比分子量为2 $\times 10^{20}$ cm $^{-2}$(K km s $^{-1}$)$^{-1}$的转换因子$X_{\rm CO}$大4倍.我们还讨论了两个高质量的YSO之间的性质的差异,其中每一个都与一个分子团的质量约为几个$\times 10^3 M_{\odot}$。

英文摘要:

We have performed Atacama Large Millimeter/submillimeter Array (ALMA) observations in $^{12}$CO($J=2-1$), $^{13}$CO($J=2-1$), C$^{18}$O($J=2-1$), $^{12}$CO($J=3-2$), $^{13}$CO($J=3-2$), and CS($J=7-6$) lines toward the active star-forming region N83C in the Small Magellanic Cloud (SMC), whose metallicity is $\sim$ 1/5 of the Milky Way (MW). The ALMA observations first reveal sub-pc scale molecular structures in $^{12}$CO($J=2-1$) and $^{13}$CO($J=2-1$) emission. We found strong CO peaks associated with young stellar objects (YSOs) identified by the $Spitzer$ Space Telescope, and also found that overall molecular gas is distributed along the edge of the neighboring HII region. We derived a gas density of $\sim 10^4$ cm$^{-3}$ in molecular clouds associated with YSOs based on the virial mass estimated from $^{12}$CO($J=2-1$) emission. This high gas density is presumably due to the effect of the HII region under the low-metallicity (accordingly small-dust content) environment in the SMC; far-UV radiation from the HII region can easily penetrate and photo-dissociate the outer layer of $^{12}$CO molecules in the molecular clouds, and thus only the innermost parts of the molecular clouds are observed even in $^{12}$CO emission. We obtained the CO-to-H$_2$ conversion factor $X_{\rm CO}$ of $7.5 \times 10^{20}$ cm$^{-2}$ (K km s$^{-1}$)$^{-1}$ in N83C based on virial masses and CO luminosities, which is four times larger than that in the MW, 2 $\times 10^{20}$ cm$^{-2}$ (K km s$^{-1}$)$^{-1}$. We also discuss the difference in the nature between two high-mass YSOs, each of which is associated with a molecular clump with a mass of about a few $\times 10^3 M_{\odot}$.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

↑