Sgr B2的异常红外辐射：可能的平面C $_{24}$
Unusual Infrared Emission toward Sgr B2: Possible Planar C$_{24}$
摘要：
星际石墨烯可能存在于星际介质（ISM）中，是由多环芳烃（PAH）分子的光化学处理和/或石墨颗粒的碰撞破碎产生的。事实上，通过比较观察到的漫射ISM的紫外（UV）消光和红外（IR）发射与石墨烯的预测，在不违反观测约束的情况下，星际碳总量的$\sim$ 2%可能被锁定在石墨烯中。虽然有报道称，在几个银河系和河外行星状星云中可能探测到平面C $_{24}$（一小片石墨烯片），但在星际环境中尚未探测到石墨烯。在这项工作中，我们寻找C $_{24}$在$\sim$ 6.6，9.8，20 $μm$的红外特征，向Sgr B2，一个高质量的恒星形成区，并找到一个候选目标，向R. A。（J2000）= $267^{\circ}.05855$和Decl.（J2000）= $-28^{\circ}.01479$，其Spitzer/IRS光谱显示出峰值在$\sim$ 6.637、9.853和20.050 $μm$的三个谱带，这似乎与C $_{24}$的谱带一致。C $_{60}$的可能特征也见于该区域。候选区域是一个被大质量恒星或星团加热的温暖尘埃环境，与一个WISE点（恒星形成活动的示踪物）有关，靠近HII区域候选IRAS 17450-2759，周围环绕着$\sim$ 5 $^{\prime}$内的七个年轻恒星候选体，这表明C $_{24}$的产生和/或激发可能与恒星形成活动有关。
英文摘要：
Interstellar graphene could be present in the interstellar medium (ISM), resulting from the photochemical processing of polycyclic aromatic hydrocarbon (PAH) molecules and/or collisional fragmentation of graphitic particles. Indeed, by comparing the observed ultraviolet (UV) extinction and infrared (IR) emission of the diffuse ISM with that predicted for graphene, as much as $\sim$ 2% of the total interstellar carbon could have been locked up in graphene without violating the observational constraints. While the possible detection of planar C$_{24}$, a small piece of a graphene sheet, has been reported towards several Galactic and extragalactic planetary nebulae, graphene has not yet been detected in interstellar environments. In this work, we search for the characteristic IR features of C$_{24}$ at $\sim$ 6.6, 9.8, 20 $μm$ toward Sgr B2, a high-mass star formation region, and find a candidate target toward R.A. (J2000) = $267^{\circ}.05855$ and Decl. (J2000) = $-28^{\circ}.01479$ in Sgr B2 whose Spitzer/IRS spectra exhibit three bands peaking at $\sim$ 6.637, 9.853 and 20.050 $μm$ which appear to be coincident with that of C$_{24}$. Possible features of C$_{60}$ are also seen in this region. The candidate region is a warm dust environment heated by massive stars or star clusters, associated with a WISE spot (a tracer of star-formation activity), close to the HII region candidate IRAS 17450-2759, and is surrounded by seven young stellar object candidates within $\sim$ 5$^{\prime}$, suggesting that the creation and/or excitation of C$_{24}$ could be related to star formation activities.
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