AI 中文总结
通过分析z=5.7的AGN宿主星系RUBIES-EGS-9809，发现大质量星系可在尘埃遮蔽阶段已形成年老恒星并熄灭，提出AGN反馈驱动的快速熄灭“尘埃路径”假说。
AI 中文摘要
我们对RUBIES-EGS-9809进行了光谱-测光分析，这是一个红移z=5.7的宽线AGN宿主星系，具有巴尔默跃变和主导的点源。该源受到尘埃红化（A_V>3星等），显示出热尘埃和冷尘埃辐射，并且是X射线康普顿厚的，其X射线与热光度之比与明亮AGN一致。大的A_V与强的NaI吸收（等效宽度=17±2埃）相符，可能来自中性气体外流（3σ），而宽的[O III]线示踪了电离外流，表明AGN反馈可能正在影响宿主星系。我们估计恒星质量log(M*/M_☉)=10.7±0.3，热光度L_bol~4×10^46 erg s^-1，黑洞质量log(M_BH/M_☉)~8.1（受较大系统误差影响）。分辨出的巴尔默跃变（0.1角秒，0.6千秒差距）与恒星起源一致，意味着该星系在恒星上已经年老，同时仍被严重遮蔽。这表明大质量星系在其致密、尘埃遮蔽阶段可以拥有演化后的恒星种群，与早期尘埃星暴形成过程一致。SED建模表明恒星形成率在下降，但低分辨率光谱单独无法约束近期恒星形成率，因此我们将该源视为强熄灭候选体，而非确认的星暴后系统。由于熄灭跟随恒星形成率下降，恒星形成驱动的外流不被支持，留下AGN反馈作为合理的驱动机制。我们推测这种快速反馈（约100百万年时标）可能在熄灭后阶段仍保持尘埃笼罩时促成熄灭，掩盖了原本在无尘埃情况下容易被探测到的紫外明亮熄灭阶段。到尘埃清除时，紫外明亮恒星可能已经减少，留下一个经典的无尘埃宁静星系。这种通往宁静的“尘埃路径”可能解释了在z=3-7处连接尘埃星暴与大质量宁静系统的中年熄灭前体（年龄50-100百万年）的缺失。
英文摘要
We present a spectro-photometric analysis of RUBIES-EGS-9809, a broad-line AGN host at z=5.7 with a Balmer break and a dominant point source. The source is dust reddened ($A_V>$3 mag), shows hot- and cold-dust emission, and is X-ray Compton thick, with X-ray-to-bolometric ratio consistent with luminous AGN. The large $A_V$ agrees with strong NaI absorption (EW=17$\pm 2 Å$), possibly from a neutral-gas outflow (3 $σ$), while broad [O III] traces an ionized outflow, suggesting AGN feedback may be affecting the host. We estimate a stellar mass log(M*/M$_\odot$)=10.7$\pm$0.3, Lbol$\sim4\times10^{46}$ erg s$^{-1}$ , and black-hole mass log(M$_{BH}/M_\odot)\sim8.1$ (subject to large systematics). The resolved Balmer break (0.1 arcsec, 0.6 kpc) is consistent with a stellar origin, implying the galaxy is already old in stars while still heavily obscured. This shows that massive galaxies can host evolved stellar populations during their compact, dust-obscured phase, consistent with formation in an earlier dusty starburst. SED modelling suggests a declining SFR, but low-resolution spectroscopy alone cannot constrain the recent SFR, so we treat the source as a strong quenching candidate rather than a secure post-starburst system. Because quenching follows the decline in SFR, star-formation-driven outflows are disfavoured, leaving AGN feedback as a plausible driver. We speculate that such rapid feedback ($\sim$100 Myr timescale) may precipitate quenching while the post-quenching phase stays dust-enshrouded, concealing the UV-bright quenched phase that would otherwise be easily detected, if dust free. By the time dust clears, the UV-luminous stars may have already dwindled, leaving a classic dust-free quiescent galaxy. This 'dusty path' to quiescence may explain the lack of intermediate-age quenched progenitors (ages 50-100 Myr) linking dusty starbursts to massive quiescent systems at z=3-7.
Comments23 pages, 12 figures, 5 tables. Published in the Open Journal of Astrophysics
