Extremely UV-bright starbursts at the end of cosmic reionization
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arXiv
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2025
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| author | Marques-Chaves, R. Schaerer, D. Dessauges-Zavadsky, M. Álvarez-Márquez, J. Hashimoto, T. Colina, L. Inoue, A. K. Blanco-Prieto, C. Nakazato, Y. Costantin, L. Arribas, S. Bakx, T. J. L. C. Ceverino, D. Gómez, A. Crespo Fudamoto, Y. Hagimoto, M. Hamada, A. Matsuoka, Y. Mawatari, K. Onoue, M. Osone, W. Ren, Y. W. Sugahara, Y. Terui, Y. Yoshida, N. |
| author_facet | Marques-Chaves, R. Schaerer, D. Dessauges-Zavadsky, M. Álvarez-Márquez, J. Hashimoto, T. Colina, L. Inoue, A. K. Blanco-Prieto, C. Nakazato, Y. Costantin, L. Arribas, S. Bakx, T. J. L. C. Ceverino, D. Gómez, A. Crespo Fudamoto, Y. Hagimoto, M. Hamada, A. Matsuoka, Y. Mawatari, K. Onoue, M. Osone, W. Ren, Y. W. Sugahara, Y. Terui, Y. Yoshida, N. |
| contents | We present a study of 27 very UV-bright (-22.0<MUV<-24.4) sources at z~6 identified in SHELLQs survey. Stacking their rest-frame UV spectra reveals a prominent NV1240A P-Cygni, consistent with very young (~6Myr) stellar populations dominated by massive stars. They are thus powerful and efficient ionizing starbursts with an average ionizing photon production efficiency of log(Xi_ion/Hz erg-1)=25.54. For one of these, J0217-0208 at z=6.2 (MUV=-23.4), we analyzed NIRCam and NIRSpec data. Its SED indicates a young (~5Myr), compact (reff~260pc) starburst with a stellar mass of 10^9Msun and high sSFR (~100Gyr^-1). This translates to high stellar mass and SFR surface densities, about 100x higher than typical galaxies at similar redshifts. NIRSpec further reveals strong nebular emission, for which we derive a high electron density (~10^3 cm^-3), a metallicity 12+log(O/H)=8.20 (from the direct method), and a super-solar N/O ratio (log(N/O)=-0.30). Furthermore, J0217-0208 shows broad components in several rest-optical lines, indicating powerful ionized outflows, which appear heavily obscured (E(B-V)~0.6), in contrast to the nearly dust-free stellar continuum (E(B-V)~0.01). Combined with ALMA detections of a massive, extended, and cold dust reservoir, these findings point to dusty, feedback-driven outflows carrying and pushing dust well beyond the stellar core, boosting the observed UV luminosity. Our results suggest that UV-bright galaxies at high redshift represent short-lived but extreme phases of rapid stellar mass growth, efficient ionizing photon production, and strong feedback. The extreme properties of J0217-0208, such as supersolar N/O, steep UV slope, compact size, and very high surface densities, closely mirror those of the brightest galaxies at z>10, suggesting a shared evolutionary pathway.[Abridged] |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2510_12411 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Extremely UV-bright starbursts at the end of cosmic reionization Marques-Chaves, R. Schaerer, D. Dessauges-Zavadsky, M. Álvarez-Márquez, J. Hashimoto, T. Colina, L. Inoue, A. K. Blanco-Prieto, C. Nakazato, Y. Costantin, L. Arribas, S. Bakx, T. J. L. C. Ceverino, D. Gómez, A. Crespo Fudamoto, Y. Hagimoto, M. Hamada, A. Matsuoka, Y. Mawatari, K. Onoue, M. Osone, W. Ren, Y. W. Sugahara, Y. Terui, Y. Yoshida, N. Astrophysics of Galaxies Cosmology and Nongalactic Astrophysics We present a study of 27 very UV-bright (-22.0<MUV<-24.4) sources at z~6 identified in SHELLQs survey. Stacking their rest-frame UV spectra reveals a prominent NV1240A P-Cygni, consistent with very young (~6Myr) stellar populations dominated by massive stars. They are thus powerful and efficient ionizing starbursts with an average ionizing photon production efficiency of log(Xi_ion/Hz erg-1)=25.54. For one of these, J0217-0208 at z=6.2 (MUV=-23.4), we analyzed NIRCam and NIRSpec data. Its SED indicates a young (~5Myr), compact (reff~260pc) starburst with a stellar mass of 10^9Msun and high sSFR (~100Gyr^-1). This translates to high stellar mass and SFR surface densities, about 100x higher than typical galaxies at similar redshifts. NIRSpec further reveals strong nebular emission, for which we derive a high electron density (~10^3 cm^-3), a metallicity 12+log(O/H)=8.20 (from the direct method), and a super-solar N/O ratio (log(N/O)=-0.30). Furthermore, J0217-0208 shows broad components in several rest-optical lines, indicating powerful ionized outflows, which appear heavily obscured (E(B-V)~0.6), in contrast to the nearly dust-free stellar continuum (E(B-V)~0.01). Combined with ALMA detections of a massive, extended, and cold dust reservoir, these findings point to dusty, feedback-driven outflows carrying and pushing dust well beyond the stellar core, boosting the observed UV luminosity. Our results suggest that UV-bright galaxies at high redshift represent short-lived but extreme phases of rapid stellar mass growth, efficient ionizing photon production, and strong feedback. The extreme properties of J0217-0208, such as supersolar N/O, steep UV slope, compact size, and very high surface densities, closely mirror those of the brightest galaxies at z>10, suggesting a shared evolutionary pathway.[Abridged] |
| title | Extremely UV-bright starbursts at the end of cosmic reionization |
| topic | Astrophysics of Galaxies Cosmology and Nongalactic Astrophysics |
| url | https://arxiv.org/abs/2510.12411 |