The baryon cycle is crucial for understanding galaxy formation, as gas inflows and outflows vary throughout a galaxy’s lifetime and affect its star formation rate. Despite the necessity of accretion for galaxy growth at high redshifts, direct observations of inflowing gas have proven elusive, especially at z ≳ 2. We present a spectroscopic analysis of a galaxy at redshift z = 2.45, which exhibits signs of inflow in several ultraviolet interstellar absorption lines, with no clear outflow signatures. The absorption lines are redshifted by ∼250 km s−1 with respect to the systemic redshift, and C iv shows a prominent inverse P-Cygni profile. Simple stellar population models suggest that this galaxy has a low metallicity (∼5% solar), with a very young starburst of age ∼4 Myr dominating the ultraviolet luminosity. The gas inflow velocity and nebular velocity dispersion suggest an approximate halo mass of order ∼1011M⊙, a regime in which simulations predict that bursty star formation is common at this redshift. We conclude that this system is likely in the beginning of a cycle of bursty star formation, where inflow and star formation rates are high, but where supernovae and other feedback processes have not yet launched strong outflows. In this scenario, we expect the inflow-dominated phase to be observable (e.g., with net redshifted interstellar medium absorption) for only a short timescale after a starburst onset. This result represents a promising avenue for probing the full baryon cycle, including inflows, during the formative phases of low-mass galaxies at high redshifts.

中文翻译：

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在 z = 2.45 的低质量星系中探测到星暴开始时的气体流入


重子循环对于理解星系的形成至关重要，因为气体流入和流出在星系的整个生命周期中都会发生变化，并影响其恒星的形成速度。尽管在高红移下星系生长必须吸积，但事实证明，对流入的气体的直接观测是难以捉摸的，尤其是在 z ≳ 2 处。我们提出了一个红移 z = 2.45 的星系的光谱分析，它在几条紫外星际吸收线中表现出流入的迹象，没有明显的流出特征。吸收线相对于系统红移红移红移 ∼250 km s-1，C iv 显示出明显的逆 P-Cygni 剖面。简单的恒星种群模型表明，这个星系的金属丰度很低（∼5% 的太阳），一个非常年轻的星暴年龄约为 4 Myr，在紫外线光度中占主导地位。气体流入速度和星云速度色散表明光晕质量约为 ∼1011M⊙，在这个状态下，模拟预测爆发性恒星的形成在这个红移中很常见。我们得出的结论是，这个系统可能处于爆发性恒星形成周期的开始阶段，其中流入和恒星形成速率很高，但超新星和其他反馈过程尚未引发强烈的流出。在这种情况下，我们预计在星暴爆发后的短时间内可以观察到以流入为主的阶段（例如，具有净红移星际介质吸收）。这一结果为在高红移的低质量星系的形成阶段探测完整的重子循环（包括流入）提供了一条有前途的途径。