论文标题
在高红移时测量星际介质的加热和冷却：PAH和[C II]在Z〜2处形成星系的同一恒星形成星系
Measuring the Heating and Cooling of the Interstellar Medium at High redshift: PAH and [C II] Observations of the Same Star Forming Galaxies at z~2
论文作者
论文摘要
恒星的形成严重取决于星际介质（ISM）中的冷却机制；但是，在星形形成峰时期（Z〜2）处星系中气体的热性能仍然很少。理解多相ISM的一个限制因素是缺乏在同一星系中检测到的多个示踪剂，例如多环芳烃（PAH）发射，这是星际气体中关键光电加热机制的示踪剂，以及[C II]158μm良好的结构发射，主要冷却剂。我们提出了靶向[C II]的Alma带9 Z〜2星形星系中的观测值[C II]，具有强烈的Spitzer IRS检测PAH发射。所有六个星系均以灰尘连续性检测到，并略有解决。我们比较了PAH和[C II]发射的特性，并将它们的关系限制为总红外光度（LIR）和IR表面密度的函数。 [C II]在一个高信噪比（34σ）的一个星系中检测到发射，我们在第二个源上放置了安全的上限。在[C II]中未检测到的其余样品可能是由于红移不确定性和狭窄的Alma带通窗所引起的。我们的结果与文献中观察到的[C II]/LIR和PAH/LIR的赤字一致。但是，[C II]与Z〜2处的PAH发射的比率可能远低于附近尘土飞扬的星系星系中观察到的比率。这可能是由于在高Z处通过[O I]增强的冷却，更热的气体和灰尘温度和/或光电效率降低的结果，其中星际辐射和气体加热之间的耦合降低。
Star formation depends critically on cooling mechanisms in the interstellar medium (ISM); however, thermal properties of gas in galaxies at the peak epoch of star formation (z ~ 2) remain poorly understood. A limiting factor in understanding the multiphase ISM is the lack of multiple tracers detected in the same galaxies, such as Polycyclic Aromatic Hydrocarbon (PAH) emission, a tracer of a critical photoelectric heating mechanism in interstellar gas, and [C II] 158μm fine-structure emission, a principal coolant. We present ALMA Band 9 observations targeting [C II] in six z ~ 2 star-forming galaxies with strong Spitzer IRS detections of PAH emission. All six galaxies are detected in dust continuum and marginally resolved. We compare the properties of PAH and [C II] emission, and constrain their relationship as a function of total infrared luminosity (LIR) and IR surface density. [C II] emission is detected in one galaxy at high signal-to-noise (34σ), and we place a secure upper limit on a second source. The rest of our sample are not detected in [C II] likely due to redshift uncertainties and narrow ALMA bandpass windows. Our results are consistent with the deficit in [C II]/LIR and PAH/LIR observed in the literature. However, the ratio of [C II] to PAH emission at z ~ 2 is possibly much lower than what is observed in nearby dusty star-forming galaxies. This could be the result of enhanced cooling via [O I] at high-z, hotter gas and dust temperatures, and/or a reduction in the photoelectric efficiency, in which the coupling between interstellar radiation and gas heating is diminished.
