AI 中文总结
研究低红移处极紧凑星暴星系，通过IRAM 30米望远镜观测其¹²CO发射线，发现其分子气体分数低、耗尽时间短、¹²CO(2-1)/¹²CO(1-0)比值低，为星系致密化阶段分子气体性质研究提供新见解。
AI 中文摘要
致密化阶段在星系演化中起着关键作用，与恒星形成活动和结构转变紧密相连。我们识别出低红移（z~0.1）的极紧凑星暴星系（eCSB）样本，它们代表这一关键演化阶段。这些eCSB是具有强烈恒星形成和高红外光度的大质量异常星系，结构已类似宁静星系。为研究其分子气体性质，我们用IRAM 30米望远镜观测了¹²CO J = 1--0和¹²CO J = 2--1发射线。结果表明eCSB分子气体分数极低（约3%）、气体耗尽时间短（约二十亿年），¹²CO(2-1)/¹²CO(1-0)比值低。这些发现为致密化阶段星系的分子气体性质提供新见解。
英文摘要
The compaction phase plays a crucial role in galaxy evolution, as it is strongly linked to star formation activities and structural transformation. We have identified a sample of extremely compact starburst galaxies (eCSBs) at low redshift~(z$\sim$0.1), which represent this critical evolutionary stage. These eCSBs are massive outliers with intense star formation and high infrared luminosities comparable to (U)LIRGs, while their structure already resembles quiescent galaxies. To investigate their molecular gas properties, we conducted IRAM 30m observations of $^{12}$CO J = 1--0 and $^{12}$CO J = 2--1 emission lines. Our results indicate that eCSBs exhibit a notably low molecular gas fraction~($\sim3\%$), and short gas depletion time~($\sim$ 20 Myr), suggesting that these galaxies are rapidly exhausting their remaining gas reservoir. Compared to normal (U)LIRGs, eCSBs show systematically lower $^{12}$CO(2-1)/$^{12}$CO(1-0) ratio~($R_{21} \sim 0.65 \pm 0.06$), similar to main sequence galaxies. The relatively low CO excitation may be associated with their high central stellar mass densities. These findings provide new insight into the molecular gas properties of galaxies during the compaction phase, highlighting their unique condition and rapid evolution toward quiescence.
CommentsAccepted for publication in ApJ, 13 pages, 8 figures, and 2 tables
