Title: Multi-wavelength properties of $z\gtrsim 6$ LISA detectable events Show Chinese title

Title: 多波长特性：LISA可探测事件的$z\gtrsim 6$

Abstract: We investigate the intrinsic and observational properties of $z\gtrsim 6$ galaxies hosting coalescing massive black holes (MBHs) that gives rise to gravitational waves (GWs) detectable with the Laser Interferometer Space Antenna (LISA). We adopt a zoom-in cosmological hydrodynamical simulation of galaxy formation and black hole (BH) co-evolution, zoomed-in on a $M_h \sim 10^{12}~\rm M_{\odot}$ dark matter halo at z = 6, which hosts a fast accreting super-massive black hole (SMBH) and a star-forming galaxy. Following the SMBH formation backward in time, we identify the merging events that concurred to its formation and we pick up the ones that are detectable with LISA. Among these LISA detectable events (LDEs), we select those that, based on their intrinsic properties are expected to be bright in one or more electromagnetic (EM) bands. We post-process these events with dust radiative transfer calculations to make predictions about their spectral energy distributions and continuum maps in the JWST to ALMA wavelength range. We compare the spectra arising from galaxies hosting the merging MBHs with those arising from AGN powered by single accreting BHs. We find that it will be impossible to identify an LDE from the continuum SEDs because of the absence of specific imprints from the merging MBHs. We also compute the profile of the H$_{\rm \alpha}$ line arising from LDEs, considering the contribution from their star-forming regions and the accreting MBHs. We find that the presence of two accreting MBHs would be difficult to infer even if both MBHs accrete at super-Eddington rates. We conclude that the combined detection of GW and EM signals from $z\gtrsim 6$ MBHs is challenging not only because of the poor sky-localization provided by LISA, but also because the loudest GW emitters are not massive enough to leave significant signatures in the emission lines arising from the broad line region. Show Chinese abstract

Abstract: 我们研究了包含正在合并的超大质量黑洞（MBH）并产生可被激光干涉仪空间天线（LISA）探测到的引力波（GW）的$z\gtrsim 6$星系的固有和观测特性。 我们采用了一个关于星系形成和黑洞（BH）共同演化的嵌套式宇宙学流体动力学模拟，该模拟聚焦于红移 z = 6 的$M_h \sim 10^{12}~\rm M_{\odot}$暗物质晕，其中包含一个快速吸积的超大质量黑洞（SMBH）和一个恒星形成星系。 通过逆时追踪 SMBH 的形成过程，我们识别出促成其形成的合并事件，并挑选出那些可以被 LISA 探测到的事件。 在这类 LISA 可探测事件（LDEs）中，我们选择那些基于其固有属性预计会在一个或多个电磁（EM）波段上明亮的事件。 我们用尘埃辐射转移计算对这些事件进行后处理，以预测它们在 JWST 到 ALMA 波长范围内的谱能量分布和连续谱图。 我们将包含合并 MBH 的星系产生的光谱与由单一吸积黑洞驱动的活动星系核（AGN）产生的光谱进行比较。 我们发现，由于缺乏合并 MBH 的特定印记，从连续谱 SED 中识别 LDE 是不可能的。 我们还计算了由 LDE 引发的 H$_{\rm \alpha}$线轮廓，考虑了其恒星形成区和吸积 MBH 的贡献。 我们发现，即使两个 MBH 都以超爱丁顿率吸积，也很难推断出存在两个吸积 MBH。 我们得出结论，来自$z\gtrsim 6$MBH 的引力波和电磁信号的联合检测不仅因为 LISA 提供的天球定位较差而具有挑战性，而且因为最响亮的引力波发射器的质量不足以在宽线区发出的发射线中留下显著特征。