标题： CECILIA：宇宙中午暗弱星系的超深休息-光学光谱 显示英文标题

标题： CECILIA: Ultra-Deep Rest-Optical Spectra of Faint Galaxies at Cosmic Noon

摘要： Intrinsically faint galaxies at $z\sim2-3$ offer critical insights into early galaxy formation, tracing low-metallicity, low-mass systems during Cosmic Noon and serving as analogs to reionization-era galaxies. We present ultra-deep JWST/NIRSpec spectroscopy of nine low-luminosity galaxies ($-17 \lesssim M_{\rm UV} \lesssim -20$, $M_\star \lesssim 10^9\,M_\odot$) at $z\sim2.5$ from the CECILIA program, with $\sim$29.5 hr in G235M/F170LP and 1 hr in G395M/F290LP. Our sample includes four LAEs, three rest-UV color-selected galaxies, and two serendipitous detections -- providing the most sensitive rest-optical spectra of individual faint galaxies at this epoch to date. Balmer-line measurements reveal low SFRs ($0.63 < \mathrm{SFR}/(M_\odot\,\mathrm{yr}^{-1}) < 5.43$) and a broad range of dust reddening ($0 < E(B-V) < 1$), with SFRs systematically below those of continuum-selected galaxies. 电子密度较低（$n_e \lesssim 200$cm$^{-3}$），发射线诊断表明低 [NII]/H$\alpha$，高 [OIII]/H$\beta$，表明金属含量$12+\log({\rm O/H})\lesssim8.0$。我们还首次提出了这种微弱高红移星系的 O1-BPT 约束。 值得注意的是，两个星系显示低 [OIII]/H$\beta$，尽管高 Ly$\alpha$EWs 和非常低的 [NII]/H$\alpha$，这与在极低金属丰度下该比值的预测转折一致——强调了需要互补诊断方法（例如，N2，O32）来识别贫金属系统。 基于$T_e$的直接 abundances 和扩展样本对于进一步追踪低质量星系中的金属丰度和电离趋势是必要的。 显示英文摘要

摘要： Intrinsically faint galaxies at $z\sim2-3$ offer critical insights into early galaxy formation, tracing low-metallicity, low-mass systems during Cosmic Noon and serving as analogs to reionization-era galaxies. We present ultra-deep JWST/NIRSpec spectroscopy of nine low-luminosity galaxies ($-17 \lesssim M_{\rm UV} \lesssim -20$, $M_\star \lesssim 10^9\,M_\odot$) at $z\sim2.5$ from the CECILIA program, with $\sim$29.5 hr in G235M/F170LP and 1 hr in G395M/F290LP. Our sample includes four LAEs, three rest-UV color-selected galaxies, and two serendipitous detections -- providing the most sensitive rest-optical spectra of individual faint galaxies at this epoch to date. Balmer-line measurements reveal low SFRs ($0.63 < \mathrm{SFR}/(M_\odot\,\mathrm{yr}^{-1}) < 5.43$) and a broad range of dust reddening ($0 < E(B-V) < 1$), with SFRs systematically below those of continuum-selected galaxies. Electron densities are low ($n_e \lesssim 200$cm$^{-3}$), and emission-line diagnostics indicate low [NII]/H$\alpha$, high [OIII]/H$\beta$, suggesting metallicities $12+\log({\rm O/H})\lesssim8.0$. We also present the first O1-BPT constraints in such faint high-redshift galaxies. Notably, two galaxies show low [OIII]/H$\beta$ despite high Ly$\alpha$ EWs and very low [NII]/H$\alpha$, consistent with the predicted turnover in this ratio at very low metallicities -- highlighting the need for complementary diagnostics (e.g., N2, O32) to identify metal-poor systems. Direct $T_e$-based abundances and expanded samples are needed to further trace metallicity and ionization trends in low-mass galaxies.