In the black hole (BH)–galaxy co-evolution framework, most of the star formation (SF) and the BH accretion are expected to take place in highly obscured conditions. The large amount of gas and dust absorbs most of the UV-to-soft-X radiation and re-emits it at longer wavelengths, mostly in the IR. Thus, obscured active galactic nuclei (AGN) are very difficult to identify in optical or X-ray bands but shine bright in the IR. Moreover, X-ray background (XRB) synthesis models predict that a large fraction of the yet-unresolved XRB is due to the most obscured (Compton thick, CT: N $_{\text{H}}\ge 10^{24} \,\mathrm{cm}^{-2}$ ) of these AGN. In this work, we investigate the synergies between putative IR missions [using SPace Infrared telescope for Cosmology and Astrophysics (SPICA), proposed for European Space Agency (ESA)/M5 but withdrawn in 2020 October, and Origins Space Telescope, OST, as ‘templates’] and the X-ray mission Athena (Advanced Telescope for High ENergy Astrophysics), which should fly in early 2030s, in detecting and characterising AGN, with a particular focus on the most obscured ones. Using an XRB synthesis model, we estimated the number of AGN and the number of those which will be detected in the X-rays by Athena. For each AGN, we associated an optical-to-Far InfraRed (FIR) spectral energy distribution (SED) from observed AGN with both X-ray data and SED decomposition and used these SEDs to check if the AGN will be detected by SPICA-like or OST at IR wavelengths. We expect that, with the deepest Athena and SPICA-like (or OST) surveys, we will be able to photometrically detect in the IR more than 90% of all the AGN (down to $L_{2-10\text{keV}} \sim 10^{42}\,\mathrm{erg\ s}^{-1}$ and up to $z \sim 10$ ) predicted by XRB synthesis modeling, and we will detect at least half of them in the X-rays. The spectroscopic capabilities of the OST can provide ${\approx}51\,000$ and ${\approx}3\,400$ AGN spectra with $R= 300$ at 25–588 $\unicode[Times]{x03BC}$ m in the wide and deep surveys, respectively, the last one up to $z\approx 4$ . Athena will be extremely powerful in detecting and discerning moderate- and high-luminosity AGN, allowing us to properly select AGN even when the mid-IR torus emission is ‘hidden’ by the host galaxy contribution. We will constrain the intrinsic luminosity and the amount of obscuration for $\sim\!20\%$ of all the AGN (and $\sim\!50\%$ of those with $L_{2-10\text{keV}} > 3.2 \times 10^{43}\,\mathrm{erg\ s}^{-1}$ ) using the X-ray spectra provided by Athena WFI. We find that the most obscured and elusive CT-AGN will be exquisitely sampled by SPICA-like mission or OST and that Athena will allow a fine characterisation of the most luminous ones. This will provide a significant step forward in the process of placing stronger constraints on the yet-unresolved XRB and investigating the BH accretion rate evolution up to very high redshift ( $z \ge 4$ ).

中文翻译：

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类似 SPICA 的任务和起源太空望远镜在寻求严重模糊的 AGN 和与雅典娜的协同作用中的作用

在黑洞（BH）-星系共同演化框架中，大部分恒星形成（SF）和 BH 吸积预计将发生在高度模糊的条件下。大量的气体和尘埃吸收了大部分的 UV 到软 X 辐射，并以更长的波长重新发射，主要是在 IR 中。因此，模糊的活动星系核（AGN）很难在光学或 X 射线波段中识别，但在红外波段中却很亮。此外，X 射线背景 (XRB) 合成模型预测，大部分尚未解决的 XRB 是由于最模糊的（康普顿厚，CT：N $_{\text{H}}\ge 10^{24} \,\mathrm{cm}^{-2}$ ) 的这些 AGN。在这项工作中，我们研究了假定的 IR 任务之间的协同作用 [使用用于宇宙学和天体物理学的太空红外望远镜 (SPICA)，为欧洲航天局 (ESA)/M5 提出但于 2020 年 10 月撤回，以及起源太空望远镜，原声带, 作为“模板”] 和 X 射线任务雅典娜（用于高能天体物理学的高级望远镜）应该在 2030 年代初期飞行，用于检测和表征 AGN，特别关注最模糊的那些。使用 XRB 合成模型，我们估计了 AGN 的数量和将在 X 射线中检测到的数量雅典娜. 对于每个 AGN，我们将观测到的 AGN 的光学到远红外 (FIR) 光谱能量分布 (SED) 与 X 射线数据和 SED 分解相关联，并使用这些 SED 来检查 AGN 是否会被检测到斯皮卡- 类似或原声带在红外波长。我们期望，以最深雅典娜和斯皮卡- 像（或原声带) 调查，我们将能够在 IR 中以光度法检测超过 90% 的 AGN（低至 $L_{2-10\text{keV}} \sim 10^{42}\,\mathrm{erg\ s}^{-1}$ 最多 $z \sim 10$ ) 由 XRB 合成模型预测，我们将在 X 射线中检测到至少一半。光谱仪的能力原声带可以提供 ${\约}51\,000$ 和 ${\约}3\,400$ AGN光谱与 $R= 300$ 在 25–588 $\unicode[次]{x03BC}$ m分别在广泛和深度调查中，最后一个直到 $z\约 4$ .雅典娜在探测和辨别中等和高亮度活动星系核方面将非常强大，即使中红外环面发射被宿主星系的贡献“隐藏”，我们也能正确选择活动星系核。我们将限制内在光度和遮蔽量 $\sim\!20\%$ 所有的 AGN（和 $\sim\!50\%$ 那些有 $L_{2-10\text{keV}} > 3.2 \times 10^{43}\,\mathrm{erg\ s}^{-1}$ ) 使用由提供的 X 射线光谱雅典娜 WFI. 我们发现最模糊和难以捉摸的 CT-AGN 将被斯皮卡- 类似任务或原声带然后雅典娜将允许对最发光的那些进行精细表征。这将在对尚未解决的 XRB 施加更强的约束并研究 BH 吸积率演变到非常高的红移的过程中向前迈出重要一步（ $z \ge 4$ ）。