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arXiv 2110.09705astro-ph.GAastro-ph.CO
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强类星体中多环芳烃的电离和破坏

The Ionization and Destruction of Polycyclic Aromatic Hydrocarbons in Powerful Quasars

Yanxia Xie, Luis C. Ho

摘要:

重新分析了86个低红移($z < 0.5$)Palomar-Green类星体的中红外(5-40 $μ$ m)Spitzer光谱,研究了多环芳烃(PAH)发射的性质及其作为发光活动星系核(AGN)宿主星系恒星形成率(SFR)指标的实用性.我们分解的光谱与我们最近开发的模板拟合技术来测量PAH通量和上限,我们解释使用模拟光谱,模拟活动星系核稀释的影响。虽然发光的类星体可以严重稀释并影响发射线的可探测性,但在一些富含气体和积极形成恒星的来源中,多环芳烃本质上很弱,最终证明强大的活动星系核会破坏多环芳烃分子。将基于多环芳烃的SFR与从中红外精细结构霓虹线和总红外光度导出的独立SFR进行比较,发现多环芳烃可以用热光度$\lesssim 10^{46}\, \rm erg\,s^{-1}$追踪类星体中的恒星形成活动,但越来越低估了更强大类星体的SFR,通常是通过$\sim 0.5$ dex。相对于恒星形成星系和低光度活动星系核,类星体的PAH为11.3 $μ$ m/7.7 $μ$ m比率,但特征性地较低比率为6.2 $μ$ m/7.7 $μ$ m,8.6 $μ$ m/7.7 $μ$ m,和11.3 $μ$ m/17.0 $μ$ m。我们认为,这些趋势表明,强大的活动星系核优先破坏小颗粒和增强PAH电离分数。

英文摘要:

We reanalyze the mid-infrared (5-40 $μ$m) Spitzer spectra of 86 low-redshift ($z < 0.5$) Palomar-Green quasars to investigate the nature of polycyclic aromatic hydrocarbon (PAH) emission and its utility as a star formation rate (SFR) indicator for the host galaxies of luminous active galactic nuclei (AGNs). We decompose the spectra with our recently developed template-fitting technique to measure PAH fluxes and upper limits, which we interpret using mock spectra that simulate the effects of AGN dilution. While luminous quasars can severely dilute and affect the detectability of emission lines, PAHs are intrinsically weak in some sources that are otherwise gas-rich and vigorously forming stars, conclusively demonstrating that powerful AGNs destroy PAH molecules. Comparing PAH-based SFRs with independent SFRs derived from the mid-infrared fine-structure neon lines and the total infrared luminosity reveals that PAHs can trace star formation activity in quasars with bolometric luminosities $\lesssim 10^{46}\, \rm erg\,s^{-1}$, but increasingly underestimate the SFR for more powerful quasars, typically by $\sim 0.5$ dex. Relative to star-forming galaxies and low-luminosity AGNs, quasars have a comparable PAH 11.3 $μ$m/7.7 $μ$m ratio but characteristically lower ratios of 6.2 $μ$m/7.7 $μ$m, 8.6 $μ$m/7.7 $μ$m, and 11.3 $μ$m/17.0 $μ$m. We suggest that these trends indicate that powerful AGNs preferentially destroy small grains and enhance the PAH ionization fraction.

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