论文标题
银河中心的大量年轻恒星物体。 ii。透过冰块富含冰的信封
Massive Young Stellar Objects in the Galactic Center. II. Seeing Through the Ice-rich Envelopes
论文作者
论文摘要
为了研究银河系中央分子区（CMZ）中星际冰的人口统计，我们使用Maunakea的NASA IRTF/SPEX获得了$ 109 $红点源的近红外光谱。我们从近红外光度法中选择样本，包括本系列上一篇论文中的$ 12 $对象，以确保这些来源在每种视线中通过云吸收大量吸收。我们发现，大多数样品（$ 100 $的对象）以$ 2.3 \μ$ m的价格显示CO带头吸收，将它们标记为红色（超级）巨人。尽管具有光电签名，但是，$ l $ band Spectra（$ 9/82 = 0.11 $）的样本中的一小部分表现出大H $ _2 $ _2 $ o冰柱密度（$ n> 2 \ times10^{18} {\ rm cm cm cm cm}^{ - 2} $），也显示了六个$ _3 $ _3 $ _3 $ _3 $ _3 $ _3 $ _3 $ _3 $ OH。由于这样的对象之一在我们以前的工作中被确定为年轻的恒星对象（YSO），因此这些冰的视力线可能与背景恒星相关，以投射到YSO或密集的云芯的扩展信封。此类对象在恒星演化的早期阶段的低频意味着恒星形成率（$ <0.02 \ m_ \ odot $ yr $^{ - 1} $），从而在CMZ中加强了先前的抑制星形构型活动的主张。 Our data also indicate that the strong "shoulder" CO$_2$ ice absorption at $15.4\ μ$m observed in YSO candidates in the previous paper arises from CH$_3$OH-rich ice grains having a large CO$_2$ concentration [$N {\rm (CO_2)} / N {\rm (CH_3OH)} \approx 1/3$].
To study the demographics of interstellar ices in the Central Molecular Zone (CMZ) of the Milky Way, we obtain near-infrared spectra of $109$ red point sources using NASA IRTF/SpeX at Maunakea. We select the sample from near- and mid-infrared photometry, including $12$ objects in the previous paper of this series, to ensure that these sources trace a large amount of absorption through clouds in each line of sight. We find that most of the sample ($100$ objects) show CO band-head absorption at $2.3\ μ$m, tagging them as red (super-) giants. Despite the photospheric signature, however, a fraction of the sample with $L$-band spectra ($9/82=0.11$) exhibit large H$_2$O ice column densities ($N > 2\times10^{18}\ {\rm cm}^{-2}$), and six of them also reveal CH$_3$OH ice absorption. As one of such objects is identified as a young stellar object (YSO) in our previous work, these ice-rich sight lines are likely associated with background stars in projection to an extended envelope of a YSO or a dense cloud core. The low frequency of such objects in the early stage of stellar evolution implies a low star-formation rate ($<0.02\ M_\odot$ yr$^{-1}$), reinforcing the previous claim on the suppressed star-formation activity in the CMZ. Our data also indicate that the strong "shoulder" CO$_2$ ice absorption at $15.4\ μ$m observed in YSO candidates in the previous paper arises from CH$_3$OH-rich ice grains having a large CO$_2$ concentration [$N {\rm (CO_2)} / N {\rm (CH_3OH)} \approx 1/3$].
