标题： 气体压缩和消耗的淬火：红移为2.57的大质量射电星系案例研究 显示英文标题

标题： Quenching by gas compression and consumption: A case study of a massive radio galaxy at z = 2.57

摘要： 本工作的目标是研究活动星系核（AGN）如何影响宿主星系中的恒星形成。 我们基于VLT/X-SHOOTER和ALMA的观测，对一个$z=2.57$大质量射电星系进行了详细的恒星形成历史和条件的研究。 深部红移紫外光谱包含光球吸收线和风特征，表明存在O型和B型恒星。 最显著检测到的光球特征用于表征最近的恒星形成：既不是瞬时的也不是连续的恒星形成历史与Si II$\lambda$1485和S V$\lambda$1502吸收的相对强度一致。 相反，至少在最近的过去发生了两次恒星形成爆发，分别发生在$6^{+1}_{-2}$百万年和$\gtrsim20$百万年前。 我们根据对[C I]$^3$P$_{2}$-$^3$P$_{1}$发射的ALMA观测，推导出分子$_{2}$气体质量为$(3.9\pm1.0)\times10^{10}$ M$_{\odot}$。分子气体质量仅为恒星质量的13%。 结合其高恒星形成率（$1020^{+190}_{-170}$）Myr，这表明恒星形成效率为$(26\pm8$) Gyr$^{-1}$，并且气体耗尽时间较短，为$(38\pm12)$ Myr。 我们将高效的恒星形成归因于压缩气体运动，以解释光球层线和由[C I]示踪的恒星形成气体的适度速度弥散度（$\leqslant$ 55 km s$^{-1}$）。 由于射电源可能非常年轻，我们的研究结果表明，剧烈的恒星形成消耗了大部分气体，并与活动星系核协同作用，去除任何残留的分子气体，并最终抑制大质量星系中的恒星形成。 显示英文摘要

摘要： The objective of this work is to study how active galactic nuclei (AGN) influence star formation in host galaxies. We present a detailed investigation of the star-formation history and conditions of a $z=2.57$ massive radio galaxy based on VLT/X-SHOOTER and ALMA observations. The deep rest-frame ultraviolet spectrum contains photospheric absorption lines and wind features indicating the presence of OB-type stars. The most significantly detected photospheric features are used to characterize the recent star formation: neither instantaneous nor continuous star-formation history is consistent with the relative strength of the Si II $\lambda$1485 and S V $\lambda$1502 absorption. Rather, at least two bursts of star formation took place in the recent past, at $6^{+1}_{-2}$ Myr and $\gtrsim20$ Myr ago, respectively. We deduce a molecular H$_{2}$ gas mass of $(3.9\pm1.0)\times10^{10}$ M$_{\odot}$ based on ALMA observations of the [C I] $^3$P$_{2}$-$^3$P$_{1}$ emission. The molecular gas mass is only 13 % of its stellar mass. Combined with its high star-formation rate of ($1020^{+190}_{-170}$) Myr, this implies a high star-formation efficiency of $(26\pm8$) Gyr$^{-1}$ and a short depletion time of $(38\pm12)$ Myr. We attribute the efficient star formation to compressive gas motions in order to explain the modest velocity dispersions ($\leqslant$ 55 km s$^{-1}$) of the photospheric lines and of the star-forming gas traced by [C I]. Because of the likely very young age of the radio source, our findings suggest that vigorous star formation consumes much of the gas and works in concert with the AGN to remove any residual molecular gas, and eventually quenching star formation in massive galaxies.