The Origins of [C ii] Emission in Local Star-forming Galaxies
The Origins of [C ii] Emission in Local Star-forming Galaxies
复制标题
DOI：
10.3847/1538-4357/aa8035
复制
发表时间：
2017-07
期刊：
影响因子：
--
通讯作者：
K. Croxall;J. Smith;E. Pellegrini;B. Groves;A. Bolatto;R. Herrera-Camus;K. Sandstrom;B. Draine;M. Wolfire;L. Armus;M. Boquien;B. Brandl;D. Dale;M. Galametz;L. Hunt;R. Kennicutt;K. Kreckel;D. Rigopoulou;P. V. D. Werf;C. Wilson
中科院分区：
文献类型：
--
作者：
K. Croxall;J. Smith;E. Pellegrini;B. Groves;A. Bolatto;R. Herrera-Camus;K. Sandstrom;B. Draine;M. Wolfire;L. Armus;M. Boquien;B. Brandl;D. Dale;M. Galametz;L. Hunt;R. Kennicutt;K. Kreckel;D. Rigopoulou;P. V. D. Werf;C. Wilson
[C II]158μm精细结构线是在本地恒星形成星系中观测到的最亮的发射线。作为气相星际介质的主要冷却剂，[C II]平衡了加热，包括通过光电效应加热气体的远紫外线光子。然而，[C II]发射的来源尚不清楚，因为C+可以在星际介质的多个相中找到。在这里，我们测量了来自附近星系样本的电离气相和中性气相的[C II]发射的比例。我们使用[N II]205μm精细结构线来追踪电离介质，从而消除了[C II]/[N II]122μm比值中存在的强烈的密度依赖性。利用翠鱼探测到的FIR[C II]和[N II]发射(对附近星系的关键洞察：用赫歇尔进行的远红外观测)和超越峰赫歇尔计划，我们表明60%-80%的[C II]发射来自中性气体。我们发现，来自中性介质的[CⅡ]分数与尘埃温度和恒星形成表面密度的关系较弱，而与气相金属丰度的关系较强。在金属丰富的环境中，相对较冷的电离气体对总[C II]排放的贡献比低丰度时大得多，这与之前的预期相反。给出了这一金属丰度趋势的近似标定。
The [C ii] 158 μm fine-structure line is the brightest emission line observed in local star-forming galaxies. As a major coolant of the gas-phase interstellar medium, [C ii] balances the heating, including that due to far-ultraviolet photons, which heat the gas via the photoelectric effect. However, the origin of [C ii] emission remains unclear because C+ can be found in multiple phases of the interstellar medium. Here we measure the fractions of [C ii] emission originating in the ionized and neutral gas phases of a sample of nearby galaxies. We use the [N ii] 205 μm fine-structure line to trace the ionized medium, thereby eliminating the strong density dependence that exists in the ratio of [C ii]/[N ii] 122 μm. Using the FIR [C ii] and [N ii] emission detected by the KINGFISH (Key Insights on Nearby Galaxies: a Far- Infrared Survey with Herschel) and Beyond the Peak Herschel programs, we show that 60%–80% of [C ii] emission originates from neutral gas. We find that the fraction of [C ii] originating in the neutral medium has a weak dependence on dust temperature and the surface density of star formation, and has a stronger dependence on the gas-phase metallicity. In metal-rich environments, the relatively cooler ionized gas makes substantially larger contributions to total [C ii] emission than at low abundance, contrary to prior expectations. Approximate calibrations of this metallicity trend are provided.