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arXiv 2009.09098astro-ph.GA
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大质量恒星形成团中[C II ]谱线发射的特征

Characterizing [C II] Line Emission In Massive Star Forming Clumps

James M. Jackson, David Allingham, Nicholas Killerby-Smith, J. Scott Whitaker, Howard A. Smith, Yanett Contreras, Andres E. Guzman, Taylor Hogge, Patricio Sanhueza, Ian W. Stephens

摘要:

由于157.74微米[C II]线是恒星形成区的主要冷却剂,它经常被用来推断星系的恒星形成率。通过表征[C II]和来自附近银河系恒星形成分子团的远红外辐射,有可能确定河外[C II]辐射是否来自大量的此类团簇,以及[C II]是否确实是全球恒星形成的可靠指标。我们描述了[C II]和远红外观测使用的FIFI-LS仪器的SOFIA航空天文台对四个密集的,高质量的银河系团块。尽管远红外光度相似,但[C II]与远红外光度比L([C II])/L(FIR)在这四个团块中变化至少140倍。特别地,对于AGAL 313.576 +0.324,尽管FIR光度为24,000 L_sun,但没有检测到[C II]线发射。AGAL 313.576 +0.324比星系的L([C Ⅱ])/L(FIR)与S_v(63 μ m)/S_v(158 μ m)的经验相关曲线低100倍以上。AGAL 313.576 +0.324可能处于早期演化的“原恒星”阶段,紫外线通量不足以吸收碳,或者处于深度嵌入的“超紧凑”H II区域阶段,其中紫外线通量的尘埃衰减将电离碳区域限制在无法检测的小体积内。或者,其明显缺乏\cii \,发射可能源于\cii \的深吸收,158微米连续谱线,或前景材料对较亮谱线发射的自吸收,这可能抵消或减少FIFI-LS仪器的宽光谱分辨率元素(~250 km/s)内的任何发射。

英文摘要:

Because the 157.74 micron [C II] line is the dominant coolant of star-forming regions, it is often used to infer the global star-formation rates of galaxies. By characterizing the [C II] and far-infrared emission from nearby Galactic star-forming molecular clumps, it is possible to determine whether extragalactic [C II] emission arises from a large ensemble of such clumps, and whether [C II] is indeed a robust indicator of global star formation. We describe [C II] and far-infrared observations using the FIFI-LS instrument on the SOFIA airborne observatory toward four dense, high-mass, Milky Way clumps. Despite similar far-infrared luminosities, the [C II] to far-infrared luminosity ratio, L([C II])/L(FIR) varies by a factor of at least 140 among these four clumps. In particular, for AGAL313.576+0.324, no [C II] line emission is detected despite a FIR luminosity of 24,000 L_sun. AGAL313.576+0.324 lies a factor of more than 100 below the empirical correlation curve between L([C II])/L(FIR) and S_ν(63 micron)/S_ν(158 micron) found for galaxies. AGAL313.576+0.324 may be in an early evolutionary "protostellar" phase with insufficient ultraviolet flux to ionize carbon, or in a deeply embedded ``hypercompact' H II region phase where dust attenuation of UV flux limits the region of ionized carbon to undetectably small volumes. Alternatively, its apparent lack of \cii\, emission may arise from deep absorption of the \cii\, line against the 158 micron continuum, or self-absorption of brighter line emission by foreground material, which might cancel or diminish any emission within the FIFI-LS instrument's broad spectral resolution element (~250 km/s)

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