$\boldsymbol{z\approx 0.2}$–0.6 场星系的 H I 性质：对宇宙恒星形成衰减的洞见
H I Properties of Field Galaxies at $\boldsymbol{z\approx 0.2}$-0.6: Insights into Declining Cosmic Star Formation
AI总结：
本研究结合CUBS与MALS数据，对约6000个中等红移场星系进行H I 21厘米叠加探测，约束不同质量星系的中性气体含量及其红移演化，揭示宇宙恒星形成衰减或与中性氢供给下降有关。
摘要：
我们报告了对中等红移（$z\approx0.2$–0.6）星系 H I 21厘米发射的统计显著探测。通过利用 Cosmic Ultraviolet Baryon Survey（CUBS，宇宙紫外重子巡天）的多视线星系巡天数据以及 MeerKAT Absorption Line Survey（MALS，MeerKAT吸收线巡天）的深度射电观测，我们在11个独立天区中建立了一个包含约6000个经光谱证认星系的样本，以约束中等红移处的中性气体含量。这些星系覆盖广泛的恒星质量范围——$8\lesssim\log{M_\rm{star}/\rm{M}_\odot}\lesssim11$，中位数为$\langle\log{M_\rm{star}/\rm{M}_\odot}\rangle_\rm{med}\approx10$——以及宽广的红移范围——$0.24\lesssim z\lesssim0.63$，中位数为$\langle z\rangle_\rm{med}=0.44$。在所有子样本的叠加光谱中，我们探测到的发射线信号显著性均超过$4\\,σ$，观测到的总H I 21厘米线流量对应于H I质量$M_\rm{H\\;I}\approx10^{10}\rm{M}_\odot$。对于$\langle\log{M_\rm{star}/\rm{M}_\odot}\rangle\approx9.3$的低质量星系，我们发现较高的H I与恒星质量比$M_\mathrm{H\\;I}/M_\rm{star}\approx6$（$>3.7\\,σ$）。对于$\langle\log{M_\rm{star}/\rm{M}_\odot}\rangle\approx10.6$的星系，我们发现$M_\mathrm{H\\;I}/M_\rm{star}\approx0.3$（$>4.7\\,σ$）。此外，由叠加发射线信号推断的低质量和高质量场星系H I质量的红移演化，与宇宙恒星形成历史的预期高度一致。这表明普通星系总体中宇宙恒星形成活动的整体衰减可能与中性氢供给的减少有关。最后，我们的分析在距这些中等红移星系超过75 kpc的距离处揭示了显著的21厘米信号，表明其延展周围环境中存在大量H I气体储库。
英文摘要：
We report statistically significant detection of H I 21-cm emission from intermediate-redshift ($z\approx0.2$-0.6) galaxies. By leveraging multi-sightline galaxy survey data from the Cosmic Ultraviolet Baryon Survey (CUBS) and deep radio observations from the MeerKAT Absorption Line Survey (MALS), we have established a sample of $\approx6000$ spectroscopically identified galaxies in 11 distinct fields to constrain the neutral gas content at intermediate redshifts. The galaxies sample a broad range in stellar mass -- $8\lesssim\log{M_\rm{star}/\rm{M}_\odot}\lesssim11$ with a median of $\langle\log{M_\rm{star}/\rm{M}_\odot}\rangle_\rm{med}\approx10$ -- and a wide range in redshift -- $0.24\lesssim z\lesssim0.63$ with a median of $\langle z\rangle_\rm{med}=0.44$. Our detected emission-line signal exceeds $4\,σ$ significance in the stacked spectra of all subsamples, and the observed total H I 21-cm line flux translates to a H I mass $M_\rm{H\;I}\approx10^{10}\rm{M}_\odot$. We find a high H I-to-stellar mass ratio of $M_\mathrm{H\;I}/M_\rm{star}\approx6$ for low-mass galaxies with $\langle\log{M_\rm{star}/\rm{M}_\odot}\rangle \approx9.3$ ($>3.7\,σ$). For galaxies with $\langle\log{M_\rm{star}/\rm{M}_\odot}\rangle\approx10.6$, we find $M_\mathrm{H\;I}/M_\rm{star}\approx0.3$ ($>4.7\,σ$). Additionally, the redshift evolution of H I mass in both low- and high-mass field galaxies, inferred from the stacked emission-line signal, aligns well with the expectation from the cosmic star formation history. This suggests that the overall decline in the cosmic star formation activity across the general galaxy population may be connected to a decreasing supply of neutral hydrogen. Finally, our analysis has revealed significant 21-cm signals at distances greater than 75 kpc from these intermediate-redshift galaxies, indicating a substantial reservoir of H I gas in their extended surroundings.
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