arXiv 2211.096282022-11-17astro-ph.GA

在中红外线中详细观察最模糊的星系核

A Detailed Look at the Most Obscured Galactic Nuclei in the Mid-Infrared

F. R. Donnan, D. Rigopoulou, I. García-Bernete, M. Pereira-Santaella, A. Alonso-Herrero, P. F. Roche, S. Aalto, A. Hernán-Caballero, H. W. W. Spoon

备注：: Accepted for publication in A&A. 23 pages, 15 figures, 3 tables
发表信息：: A&A 669, A87 (2023)
DOI：: 10.1051/0004-6361/202244937

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摘要：

上下文致密暗核（CONs）是星系演化的一个极端阶段，在这个阶段，超大质量黑洞的快速增长和$/$或致密恒星形成活动完全被气体和尘埃所掩盖。目的。我们研究了CON在中红外的特性，并探索了旨在识别这些对象的技术，例如通过其多环芳烃（PAH）特征的等效宽度（EW）比。方法.我们模型斯皮策光谱分解成核和恒星形成的组件，然后从我们测量的核光学深度，$τ_N$，的$9.8 μ$ m硅酸盐吸收功能的连续。我们还使用斯皮策光谱图来研究PAH EW比如何随托管CON对象的孔径大小而变化。我们发现，核的光学深度，$τ_N$，强烈相关的HCN-振动发射线在毫米CON的皮尔逊相关系数为0.91。我们发现PAH EW比率技术是有效的选择CON和强大的对高度倾斜的星系，强大的尘埃带可能会模仿CON一样的光谱，产生高$τ_N$。我们对斯皮策光谱图的分析表明，当宿主星系中有一个强大的恒星形成成分时，PAH EW比率隔离CON的功效就会降低。此外，我们发现，使用推断的核光学深度是一种可靠的方法来识别CON在$36^{+8}_{-7}\%$的ULIRG和$17^{+3}_{-3}\%$的LIRGs，与以前的工作一致。结论.我们确认中红外光谱是一个强大的诊断CON的JWST的灵敏度增加将允许识别CON在宇宙中午揭示这个极端的，但隐藏的星系演化阶段。

英文摘要：

Context. Compact Obscured Nuclei (CONs) are an extreme phase of galaxy evolution where rapid supermassive black hole growth and$/$or compact star-forming activity is completely obscured by gas and dust. Aims. We investigate the properties of CONs in the mid-infrared and explore techniques aimed at identifying these objects such as through the equivalent width (EW) ratios of their Polycyclic Aromatic Hydrocarbon (PAH) features. Methods. We model Spitzer spectra by decomposing the continua into nuclear and star-forming components from which we then measure the nuclear optical depth, $τ_N$, of the $9.8 μ$m silicate absorption feature. We also use Spitzer spectral maps to investigate how PAH EW ratios vary with aperture size for objects hosting CONs. Results. We find that the nuclear optical depth, $τ_N$, strongly correlates with the HCN-vib emission line in the millimetre for CONs with a Pearson correlation coefficient of 0.91. We find the PAH EW ratios technique to be effective at selecting CONs and robust against highly inclined galaxies where strong dust lanes may mimic a CON like spectrum by producing a high $τ_N$. Our analysis of the Spitzer spectral maps showed that the efficacy of the PAH EW ratios to isolate CONs is reduced when there is a strong star-forming component from the host galaxy. In addition, we find that the use of the inferred nuclear optical depth is a reliable method to identify CONs in $36^{+8}_{-7}\%$ of ULIRGs and $17^{+3}_{-3}\%$ of LIRGs, consistent with previous work. Conclusions. We confirm mid-IR spectra to be a powerful diagnostic of CONs where the increased sensitivity of JWST will allow identification of CONs at cosmic noon revealing this extreme but hidden phase of galaxy evolution.

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