Goicoechea Javier R, Santa-Maria Miriam G, Bron Emeric, Teyssier David, Marcelino Nuria, Cernicharo José, Cuadrado Sara
Instituto de Física Fundamental (CSIC). Calle Serrano 121, E-28006, Madrid, Spain.
Telespazio Vega UK Ltd for ESA/ESAC. Urbanización Villafranca del Castillo, Villanueva de la Cañada, E-28692 Madrid, Spain.
Astron Astrophys. 2019 Feb 1;622. doi: 10.1051/0004-6361/201834409.
Young massive stars regulate the physical conditions, ionization, and fate of their natal molecular cloud and surroundings. It is important to find tracers that help quantifying the stellar feedback processes that take place at different spatial scales. We present 85 arcmin (1.3 pc) velocity-resolved maps of several submillimeter molecular lines, taken with /HIFI, toward the closest high-mass star-forming region, the Orion molecular cloud 1 core (OMC-1). The observed rotational lines include probes of warm and dense molecular gas that are difficult, if not impossible, to detect from ground-based telescopes: CH ( = 1-0), CO ( = 10-9), HCO ( = 6-5) and HCN ( = 6-5), and CH (, =1, 3/2-1, 1/2). These lines trace an extended but thin layer ( ≃3-6 mag or ~10 cm) of molecular gas at high thermal pressure, = · ≈ 10 - 10 cm K, associated with the far ultraviolet (FUV) irradiated surface of OMC-1. The intense FUV radiation field, emerging from massive stars in the Trapezium cluster, heats, compresses and photoevaporates the cloud edge. It also triggers the formation of specific reactive molecules such as CH. We find that the CH ( = 1-0) emission spatially correlates with the flux of FUV photons impinging the cloud: from ~10 to ~10. This correlation is supported by constant-pressure photodissociation region (PDR) models in the parameter space / ≈ [5 · 10 - 8 · 10] cm K where many observed PDRs seem to lie. The CH ( = 1-0) emission spatially correlates with the extended infrared emission from vibrationally excited H ( ≥ 1), and with that of [C ii] 158 μm and CO = 10-9, all emerging from FUV-irradiated gas. These correlations link the presence of CH to the availability of C ions and of FUV-pumped H ( ≥ 1) molecules. We conclude that the parsec-scale CH emission and narrow-line (Δv ≃ 3 km s) mid- CO emission arises from extended PDR gas and not from fast shocks. PDR line tracers are the smoking gun of the stellar feedback from young massive stars. The PDR cloud surface component in OMC-1, with a mass density of 120-240 pc, represents ~5% to ~10% of the total gas mass, however, it dominates the emitted line luminosity; the average CO = 10-9 surface luminosity in the mapped region being ~35 times brighter than that of CO = 2-1. These results provide insights into the source of submillimeter CH and mid- CO emission from distant star-forming galaxies.
年轻的大质量恒星调节其诞生时所在分子云及其周围环境的物理条件、电离状态和命运。找到有助于量化在不同空间尺度上发生的恒星反馈过程的示踪剂很重要。我们展示了用/HIFI拍摄的朝向最近的高质量恒星形成区域——猎户座分子云1核心（OMC - 1）的几个亚毫米分子线的约85角分（约1.3秒差距）速度分辨图谱。观测到的转动线包括对温暖且致密的分子气体的探测，这些气体即使不是不可能，也很难从地基望远镜中检测到：CH（J = 1 - 0）、CO（J = 10 - 9）、HCO（J = 6 - 5）和HCN（J = 6 - 5），以及CH（N，J = 1，3/2 - 1，1/2）。这些谱线追踪了一层延伸但很薄（柱密度≃3 - 6 mag或约10²³ cm⁻²）的处于高热压力（P/k = nT ≈ 10⁴ - 10⁵ cm⁻³ K）的分子气体，该气体与OMC - 1受远紫外（FUV）辐射的表面相关。来自猎户座梯形星团中大质量恒星的强烈FUV辐射场加热、压缩并光蒸发云边缘。它还触发了特定反应性分子如CH的形成。我们发现CH（J = 1 - 0）发射在空间上与撞击云的FUV光子通量相关：FUV通量从约10¹⁰到约10¹¹ photons cm⁻² s⁻¹。在参数空间P/k ≈ [5·10³ - 8·10⁴] cm⁻³ K中，许多观测到的光解离区域（PDR）似乎都位于此，恒压光解离区域（PDR）模型支持了这种相关性。CH（J = 1 - 0）发射在空间上与来自振动激发的H₂（v ≥ 1）的扩展红外发射相关，也与来自FUV辐射气体的[C ii] 158μm和CO（J = 10 - 9）发射相关。这些相关性将CH的存在与C⁺离子以及FUV泵浦的H₂（v ≥ 1）分子的可用性联系起来。我们得出结论，秒差距尺度的CH发射和窄线（Δv ≃ 3 km s⁻¹）中J = 10 - 9的CO发射源自扩展的PDR气体而非快速激波。PDR线示踪剂是年轻大质量恒星恒星反馈的关键证据。OMC - 1中的PDR云表面成分，质量密度为120 - 240 cm⁻³，占总气体质量的约5%至约10%，然而，它主导了发射线光度；在映射区域中，平均CO（J = 10 - 9）表面光度比CO（J = 2 - 1）亮约35倍。这些结果为遥远恒星形成星系中亚毫米CH和中J = 10 - 9的CO发射源提供了见解。
