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| Main Authors: | , , , , , , , , |
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| Format: | Preprint |
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2025
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| Subjects: | |
| Online Access: | https://arxiv.org/abs/2507.22237 |
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| _version_ | 1866912510685216768 |
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| author | Raptis, Menelaos Trainor, Ryan F. Strom, Allison L. Rudie, Gwen C. Rogers, Noah S. J. Steidel, Charles C. Maseda, Michael V. von Raesfeld, Caroline Cuestas, Nathalie A. Korhonen |
| author_facet | Raptis, Menelaos Trainor, Ryan F. Strom, Allison L. Rudie, Gwen C. Rogers, Noah S. J. Steidel, Charles C. Maseda, Michael V. von Raesfeld, Caroline Cuestas, Nathalie A. Korhonen |
| contents | 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$α$, high [OIII]/H$β$, 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$β$ despite high Ly$α$ EWs and very low [NII]/H$α$, 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. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2507_22237 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | CECILIA: Ultra-Deep Rest-Optical Spectra of Faint Galaxies at Cosmic Noon Raptis, Menelaos Trainor, Ryan F. Strom, Allison L. Rudie, Gwen C. Rogers, Noah S. J. Steidel, Charles C. Maseda, Michael V. von Raesfeld, Caroline Cuestas, Nathalie A. Korhonen Astrophysics of Galaxies 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$α$, high [OIII]/H$β$, 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$β$ despite high Ly$α$ EWs and very low [NII]/H$α$, 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. |
| title | CECILIA: Ultra-Deep Rest-Optical Spectra of Faint Galaxies at Cosmic Noon |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2507.22237 |