Polycyclic aromatic hydrocarbon (PAH) molecules are abundant and widespread throughout the Universe, as revealed by their distinctive set of emission bands at 3.3, 6.2, 7.7, 8.6, 11.3 and 12.7 μm, which are characteristic of their vibrational modes. They are ubiquitously seen in a wide variety of astrophysical regions, ranging from planet-forming disks around young stars to the interstellar medium of the Milky Way and other galaxies out to high redshifts at z ≳ 4. PAHs profoundly influence the thermal budget and chemistry of the interstellar medium by dominating the photoelectric heating of the gas and controlling the ionization balance. Here I review the current state of knowledge of the astrophysics of PAHs, focusing on their observational characteristics obtained from the Spitzer Space Telescope and their diagnostic power for probing the local physical and chemical conditions and processes. Special attention is paid to the spectral properties of PAHs and their variations revealed by the Infrared Spectrograph onboard Spitzer across a much broader range of extragalactic environments (for example, distant galaxies, early-type galaxies, galactic halos, active galactic nuclei and low-metallicity galaxies) than was previously possible with the Infrared Space Observatory or any other telescope facilities. Also highlighted is the relation between the PAH abundance and the galaxy metallicity established for the first time by Spitzer.

多环芳烃（PAH）分子在整个宇宙中分布广泛且分布广泛，其独特的发射带集为3.3、6.2、7.7、8.6、11.3和12.7μm，这是其振动模式的特征。从天体周围的行星形成盘到银河系的星际介质以及其他星系，再到z high的高红移，它们在各种各样的天体区域中无处不在。4. PAH通过控制气体的光电加热并控制电离平衡，深刻影响星际介质的热收支和化学反应。在这里，我将重点介绍PAH的天体物理学知识，重点是从Spitzer太空望远镜获得的观测特性以及它们对探测当地物理和化学条件与过程的诊断能力。Spitzer上的红外光谱仪在更广泛的银河外环境（例如，遥远的星系，早期类型的星系，银河晕，活跃的银河核和低金属性）中特别关注了PAH的光谱特性及其变化，这些变化由Spitzer上的红外光谱仪揭示星系），这是红外空间天文台或任何其他望远镜设施以前无法实现的。