AI 中文总结
本研究利用 AKARI 数据，分析 102 个本地恒星形成星系的近红外光谱，发现 PAH 脂肪族分数与金属丰度、AGN 及恒星形成活动相关，为恒星形成与 AGN 对 PAH 结构的影响提供了观测约束。
AI 中文摘要
多环芳香烃（PAH）分子在星系中大量存在且分布广泛，其红外（IR）辐射可示踪恒星形成。天文环境中的 PAH 分子常含有脂肪族成分，这可通过 3.4 微米脂肪族 C-H 伸缩振动的探测得到证实，该特征是伴随 3.3 微米芳香族 C-H 伸缩振动的弱卫星特征。本研究从 AKARI 档案中选取了 102 个本地恒星形成星系，其中 66 个包含活动星系核（AGN）。我们分析了这些星系的 AKARI 近红外光谱，其呈现出明显的 3.3 微米芳香族和 3.4 微米脂肪族 C-H 发射特征。我们还汇编了这些星系的多波段测光数据，并对其从紫外（UV）到远红外的光谱能量分布（SED）进行分解分析，以推导星系的恒星形成率（SFR）、恒星质量、金属丰度和光度。我们探究了 3.3 微米 PAH 发射光度（$L_{3.3}$）作为 SFR 校准器的适用性，发现其与前人研究结果吻合良好。我们还发现 $L_{3.3}/L_{\rm IR}$ 和 $L_{3.4}/L_{\rm IR}$ 与金属丰度存在强相关性，但在 12+log(O/H)~8.5 以上时基本保持恒定，其中 $L_{\rm IR}$ 是尘埃发射的总光度，$L_{3.4}$ 是 3.4 微米脂肪族发射的光度。我们从 $L_{3.4}/L_{3.3}$ 推导了 PAH 脂肪族分数，定义为脂肪族单元中碳原子的占比，其范围约为 0.38% 至 6.8%，中位数约为 3.1%。AGN 宿主星系的 PAH 脂肪族分数更低，且与 SFR 和 $L_{\rm IR}$ 呈弱负相关，这表明 AGN 区域或强恒星形成活动中的光子可能会光解与 PAH 分子相关的脂肪族结构。
英文摘要
Polycyclic aromatic hydrocarbon (PAH) molecules are abundant and widespread in galaxies and their infrared (IR) emission traces star formation. PAH molecules in astronomical environments often have aliphatic contents as revealed by the detection of the 3.4 micron aliphatic C--H stretch, a weak satellite feature accompanying the 3.3 micron aromatic C--H stretch. Here, we selected 102 local star-forming galaxies from the AKARI archive, including 66 galaxies each of which hosts an active galactic nucleus (AGN). We analyzed their AKARI near-IR spectra, which exhibit pronounced 3.3 micron aromatic and 3.4 micron aliphatic C--H emission. We also compiled their multi-wavelength photometric data and performed a decompositional analysis of their spectral energy distributions (SEDs) from the ultraviolet (UV) to the far-IR to derive the star formation rates (SFRs), stellar masses, metallicities, and luminosity of the galaxies. We explored the 3.3 micron PAH emission luminosity ($L_{3.3}$) as a calibrator of the SFR and found a close agreement with previous studies. We also found that $L_{3.3}/L_{\rm IR}$ and $L_{3.4}/L_{\rm IR}$ exhibit a strong dependence on metallicity, but remain nearly constant above 12+log(O/H)$\sim\,$8.5, where $L_{\rm IR}$ is the total luminosity emitted by dust, and $L_{3.4}$ is the luminosity of the 3.4 micron aliphatic emission. We derived from $L_{3.4}/L_{3.3}$ the PAH aliphatic fractions, defined as the fractions of carbon atoms in aliphatic units, to be in the range of $\sim\,$0.38%--6.8%, with a median fraction of $\sim\,$3.1%. The PAH aliphatic fractions are lower in AGN hosts and show a weak negative correlation with the SFR and $L_{\rm IR}$, suggesting that UV photons in regions with AGN or strong star formation activities may photodissociate the aliphatic structures associated with PAH molecules.
Comments45 page, 12 figure, 6 tables; accepted for publication in The Astrophysical Journal
