A Galaxy with an Extremely Blue UV Slope $β=-3$ at $z=9.25$ Identified by JWST Spectroscopy: Evidence for a Weak Nebular Continuum and Efficient Ionizing Photon Escape?
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| Autores principales: | , , , , , , , , , , |
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| Formato: | Preprint |
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2024
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| _version_ | 1866915246839431168 |
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| author | Yanagisawa, Hiroto Ouchi, Masami Nakajima, Kimihiko Harikane, Yuichi Fujimoto, Seiji Ono, Yoshiaki Umeda, Hiroya Nakane, Minami Yajima, Hidenobu Fukushima, Hajime Xu, Yi |
| author_facet | Yanagisawa, Hiroto Ouchi, Masami Nakajima, Kimihiko Harikane, Yuichi Fujimoto, Seiji Ono, Yoshiaki Umeda, Hiroya Nakane, Minami Yajima, Hidenobu Fukushima, Hajime Xu, Yi |
| contents | We investigate UV continuum slopes $β$ of 863 galaxies at $z=4-14$ using archival JWST/NIRSpec PRISM spectra obtained from major JWST GTO, ERS, and GO programs, including JADES, CEERS, and UNCOVER. Among these galaxies, we identify a remarkable galaxy at $z=9.25$, dubbed EBG-1, with a significantly blue UV slope $β=-2.99\pm0.15$, unlike the rest of the galaxies that exhibit red continua or ambiguous blue continua hindered by large uncertainties. We confirm that the $β$ value negligibly changes by the data reduction and fitting wavelength ranges for UV emission/absorption line masking. The extreme blue slope, $β=-3.0$, rules out significant contributions from dust extinction or AGN activity. Comparing with stellar and nebular emission models, we find that such a blue UV slope cannot be reproduced solely by stellar models even with very young, metal-poor, or top-heavy contiguous star formation associated with strong nebular continua making the UV slopes red, but with a high ionizing photon escape fraction, $f_\mathrm{esc}^\mathrm{ion} \gtrsim 0.5$, for a weak nebular continuum. While the H$β$ emission line is not detected, likely due to the limited sensitivity of the spectrum, we find moderately weak [O III] $λλ$4959,5007 emission lines for the given star-formation rate ($3\, \mathrm{M_\odot}$ yr$^{-1}$) and stellar mass ($10^{8.0} \, \mathrm{M_\odot}$) that are about three times weaker than the average emission lines, again suggestive of the high ionizing photon escape fraction, $f_\mathrm{esc}^\mathrm{ion} \sim 0.7$ or more. EBG-1 would provide crucial insights into stellar and nebular continuum emission in high-redshift galaxies, serving as an example of the ionizing photon escaping site at the epoch of reionization. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2411_19893 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | A Galaxy with an Extremely Blue UV Slope $β=-3$ at $z=9.25$ Identified by JWST Spectroscopy: Evidence for a Weak Nebular Continuum and Efficient Ionizing Photon Escape? Yanagisawa, Hiroto Ouchi, Masami Nakajima, Kimihiko Harikane, Yuichi Fujimoto, Seiji Ono, Yoshiaki Umeda, Hiroya Nakane, Minami Yajima, Hidenobu Fukushima, Hajime Xu, Yi Astrophysics of Galaxies We investigate UV continuum slopes $β$ of 863 galaxies at $z=4-14$ using archival JWST/NIRSpec PRISM spectra obtained from major JWST GTO, ERS, and GO programs, including JADES, CEERS, and UNCOVER. Among these galaxies, we identify a remarkable galaxy at $z=9.25$, dubbed EBG-1, with a significantly blue UV slope $β=-2.99\pm0.15$, unlike the rest of the galaxies that exhibit red continua or ambiguous blue continua hindered by large uncertainties. We confirm that the $β$ value negligibly changes by the data reduction and fitting wavelength ranges for UV emission/absorption line masking. The extreme blue slope, $β=-3.0$, rules out significant contributions from dust extinction or AGN activity. Comparing with stellar and nebular emission models, we find that such a blue UV slope cannot be reproduced solely by stellar models even with very young, metal-poor, or top-heavy contiguous star formation associated with strong nebular continua making the UV slopes red, but with a high ionizing photon escape fraction, $f_\mathrm{esc}^\mathrm{ion} \gtrsim 0.5$, for a weak nebular continuum. While the H$β$ emission line is not detected, likely due to the limited sensitivity of the spectrum, we find moderately weak [O III] $λλ$4959,5007 emission lines for the given star-formation rate ($3\, \mathrm{M_\odot}$ yr$^{-1}$) and stellar mass ($10^{8.0} \, \mathrm{M_\odot}$) that are about three times weaker than the average emission lines, again suggestive of the high ionizing photon escape fraction, $f_\mathrm{esc}^\mathrm{ion} \sim 0.7$ or more. EBG-1 would provide crucial insights into stellar and nebular continuum emission in high-redshift galaxies, serving as an example of the ionizing photon escaping site at the epoch of reionization. |
| title | A Galaxy with an Extremely Blue UV Slope $β=-3$ at $z=9.25$ Identified by JWST Spectroscopy: Evidence for a Weak Nebular Continuum and Efficient Ionizing Photon Escape? |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2411.19893 |