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arXiv 2410.10941astro-ph.GA
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蓝色类星体的近红外光谱能量分布:是什么驱动了尘埃环的演化?

The near-infrared SED of blue quasars: what drives the evolution of the dusty torus?

Bartolomeo Trefoloni, Roberto Gilli, Elisabeta Lusso, Alessandro Marconi, Giovanni Mazzolari, Emanuele Nardini, Guido Risaliti, Matilde Signorini

AI总结:

本研究通过约36,000个1型AGN的紫外、光学和近红外测光数据,分析近红外SED随红移和博洛米光度的演化,发现NIR光度随光度增加而减小,覆盖因子与光度反相关,但与红移无关,并用于约束X射线遮蔽下限。

摘要:

活动星系核(AGN)统一模型中的一个基本成分是遮蔽环,其最内部、最热的区域主导了近红外(NIR)发射。表征环性质的变化及其与主要AGN发射的相互作用,是我们理解AGN物理、演化和分类的关键。环的覆盖因子($CF$)在很大程度上决定了基于宽发射线探测的AGN分类。目前尚不清楚环的性质是否随时间演化,以及它们如何与核的吸积参数相关联。在本工作中,我们旨在研究NIR性质随红移($z$)和AGN的博洛米光度($L_{\rm bol}$)的演化。为此,我们汇编了一个包含约36,000个1型AGN的大型数据集,其红移范围在$0.5<z<2.9$,博洛米光度范围在$45.0<\log(L_{\rm bol} / (\rm erg / s))<48.0$,并具有紫外、光学和近红外测光数据。我们在$z-L_{\rm bol}$参数空间的不同区间内生成了平均光谱能量分布(SED),以估计NIR SED如何随这些参数演化。我们发现,在任何红移下,NIR光度都随$L_{\rm bol}$的增加而减小。同时,我们样本中NIR SED的形状与随$z$不演化的结论一致。因此,所有探索的$CF$代理指标均与$L_{\rm bol}$显著反相关,但与$z$无显著反相关。此外,$CF$还与爱丁顿比率($\lambda_{\rm Edd}$)表现出较浅的反相关,然而当前的系统性不确定性以及有限的动态范围,使我们无法精确约束爱丁顿比率的作用。最后,我们从NIR与光学光度之比推导出覆盖因子,并利用它来设定不同红移下X射线遮蔽的下限。

英文摘要:

A fundamental ingredient in the unified model of active galactic nuclei (AGN) is the obscuring torus, whose innermost, hottest region dominates the near infrared (NIR) emission. Characterising the change in the torus properties and its interplay with the main AGN emission is key for our understanding of AGN physics, evolution and classification. Its covering factor ($CF$) is largely responsible for the classification of AGN on the basis of the detection of broad emission lines. It is still not clear whether the torus properties evolve over time and how they relate with the accretion parameters of the nucleus. In this work, we aim at investigating the evolution of the NIR properties with the redshift ($z$) and the bolometric luminosity ($L_{\rm bol}$) of the AGN. To this end, we assembled a large dataset of $\sim$36,000 Type 1 AGN between $0.5<z<2.9$ and $45.0<\log(L_{\rm bol} / (\rm erg / s))<48.0$ with UV, optical and near-infrared photometry. We produced average spectral energy distributions (SED) in different bins of the $z-L_{\rm bol}$ parameter space to estimate how the NIR SED evolves according to these parameters. We find that the NIR luminosity decreases for increasing $L_{\rm bol}$ at any redshift. At the same, time the shape of the NIR SED in our sample is consistent with a non-evolution with $z$. As a consequence, all the explored proxies for the $CF$ exhibit significant anti-correlations with $L_{\rm bol}$, but not with $z$. Additionally, the $CF$ also shows a shallower anti-correlation with the Eddington ratio ($λ_{\rm Edd}$), yet current systematic uncertainties, as well as the limited dynamical range, do not allow us to precisely constrain the role of the Eddington ratio. Lastly, we derived the covering factor from the ratio between the NIR and optical luminosity and we employed it to set a lower limit for the X-ray obscuration at different redshifts.

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