[论文解读] Large-scale outflows in luminous QSOs revisited: The impact of beam smearing on AGN feedback efficiencies

B. Husemann, J. Scharwächter+4 more|DigitalCommons - CalPoly (California State Polytechnic University)|Dec 17, 2015

Galaxies: Formation, Evolution, Phenomena参考文献 102被引用 35

一句话总结

本研究通过量化光束弥散对活动星系核反馈能量学的影响，重新评估了明亮类星体中大尺度喷流的能量学。利用12个无遮挡类星体的积分场光谱，研究显示光束弥散会人为夸大观测到的谱线宽度和动力学功率；经过去卷积处理后，动能功率降低了1至2个数量级，反馈效率降至电波光度的0.01–0.1%，远低于宇宙学模拟中为重现大质量星系族群所需5–10%的阈值。

ABSTRACT

[Abridged] Enormous observational efforts have been made to constrain the energetics of AGN feedback by mapping the kinematics of the ionized gas on kpc scale. We study how the observed kinematics and inferred energetics are affected by beam smearing of a bright unresolved NLR due to seeing. We analyse IFU spectroscopy of a sample of twelve QSOs initially presented by Liu et al. (2014). The PSF for the observations is directly obtained from the light distribution of the broad Hb line component. We are able to compare the ionized gas kinematics and derived energetics of the total, spatially extended, and unresolved [OIII] emission. We find that the spatially resolved [OIII] line width on kpc scales is significantly narrower than the one before PSF deblending. The ENLRs appear offset from the QSO position or more elongated which can be interpreted in favour of a conical outflow on large scales while a spherical geometry cannot be excluded for the unresolved NLR. We find that the kinetic power at 5kpc distance from the spherical model by Liu et al. (2013) is reduced by two magnitudes for a conical outflow and one magnitude for the unresolved NLR after PSF deblending. This reduced kinetic power corresponds to 0.01-0.1% of the bolometric AGN luminosity. This is smaller than the 5-10% feedback efficiency required by some simulations to reproduce the massive galaxy population. The injected momentum fluxes are close or below the simple radiation-pressure limit Lbol/c for the conical outflow model for the NLR and ENLR when beam smearing is considered. IFU spectroscopy is a powerful tool to investigate the energetics of AGN outflows, but the impact of beam smearing has to be taken into account. For the majority of observations in the literature, this has not been addressed carefully so that the incidence and energetics of presumed kpc-scale AGN-driven outflows still remain an unsolved issue.

研究动机与目标

• 通过考虑光束弥散效应，重新评估明亮类星体中大尺度活动星系核驱动喷流的能量学。
• 确定仪器视宁度和点扩散函数（PSF）展宽如何扭曲扩展窄线区（ENLR）中[O iii]发射线的观测动力学。
• 量化未分辨中心[O iii]发射对推断的反馈效率和动能功率估计的影响。
• 通过评估仪器限制，解决关于遮挡类星体中普遍存在千秒差距尺度喷流与非遮挡类星体中未观测到此类特征之间的矛盾。
• 确立光束弥散是利用积分场光谱解读活动星系核反馈时一个关键且此前被低估的因素。

提出的方法

• 使用Gemini/GMOS对12个红移在0.4 < z < 0.7之间的明亮无遮挡类星体获取高分辨率光学积分场光谱。
• 直接从未分辨的宽Hβ发射成分中推导点扩散函数（PSF），实现精确的PSF去卷积。
• 利用PSF去卷积技术将总[O iii]发射分离为未分辨的中心成分和真正空间扩展的ENLR。
• 分别对解析和未解析成分重新计算动力学特性（谱线宽度、速度弥散），以评估光束弥散的影响。
• 在球形与锥形几何模型下建模喷流能量学，比较去卷积前后动能功率与动量通量的差异。
• 将反馈效率计算为5 kpc处动能功率与电波光度的比值，评估其与宇宙学模拟的一致性。

实验结果

研究问题

• RQ1 由于视宁度和PSF展宽导致的光束弥散，如何影响明亮类星体中[O iii]发射线观测到的动力学？
• RQ2 由于中心未分辨发射的存在，大尺度活动星系核喷流的推断动能功率被高估了多少？
• RQ3 在对ENLR动力学进行光束弥散校正后，反馈效率如何变化？
• RQ4 为何先前研究在遮挡类星体中报告普遍存在千秒差距尺度喷流，而在非遮挡类星体中未见此类特征？光束弥散是否为此原因的一部分？
• RQ5 光束弥散对高对比度类星体环境中活动星系核驱动喷流的动量通量与能量预算有何影响？

主要发现

• 由于光束弥散，千秒差距尺度上的空间解析[O iii]谱线宽度显著窄于总观测宽度，表明喷流速度被高估。
• 经过PSF去卷积后，锥形喷流模型的动能功率相比球形模型降低了两个数量级，5 kpc处降至1.5–3×10^41 erg/s。
• 校正后的反馈效率仅为电波光度的0.01–0.1%，远低于宇宙学模拟为重现大质量星系族群所需5–10%的阈值。
• 锥形喷流模型的动量通量接近或低于辐射压极限L_bol/c，表明动量注入不足，难以产生强反馈。
• 未分辨的NLR对观测动力学有显著贡献，其去除后揭示出与锥形喷流几何一致的内在不对称性和拉长结构。
• 光束弥散可能解释了遮挡类星体中普遍报告千秒差距尺度喷流与非遮挡类星体中缺乏此类特征之间矛盾的部分原因，尤其是在未校正仪器效应时。