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| Main Authors: | , , , , , , , , , , , , , , , , , , , , , , |
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| Format: | Preprint |
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2026
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| Online Access: | https://arxiv.org/abs/2604.16666 |
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| _version_ | 1866911603519127552 |
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| author | McLeod, D. J. Dunlop, J. S. McLure, R. J. Donnan, C. T. Begley, R. Antonogiannaki, S. Magee, D. Illingworth, G. D. Haro, P. Arrabal Bondestam, C. Carnall, A. C. Cullen, F. Dickinson, M. Ellis, R. S. Frye, B. L. Golawska, H. Grogin, N. A. Holst, I. J. B. Kamieneski, P. S. Leung, H. -H. Liu, F. -Y. Stanton, T. M. Tittley, E. R. |
| author_facet | McLeod, D. J. Dunlop, J. S. McLure, R. J. Donnan, C. T. Begley, R. Antonogiannaki, S. Magee, D. Illingworth, G. D. Haro, P. Arrabal Bondestam, C. Carnall, A. C. Cullen, F. Dickinson, M. Ellis, R. S. Frye, B. L. Golawska, H. Grogin, N. A. Holst, I. J. B. Kamieneski, P. S. Leung, H. -H. Liu, F. -Y. Stanton, T. M. Tittley, E. R. |
| contents | We present a new determination of the evolving galaxy UV luminosity function (LF) over the extreme redshift range $12.5<z<18.5$, based on a wide-area search of $>$0.6 deg$^2$ of JWST NIRCam imaging containing $>150$ independent sight-lines. We find evidence for an accelerated decline in the UV LF, and hence inferred star-formation rate density ($ρ_{\rm SFR}$), over the $\simeq100\rm{Myr}$ cosmic time interval between $z=11$ and $z=13.5$. Moreover, based on a notable lack of galaxy candidates at $z>14.5$, we find evidence for an even more rapid descent in star-formation activity towards earlier times, with our new measurement of $ρ_{\rm SFR}$ at $z\simeq15.5$ lying significantly below an extrapolation of the log-linear $ρ_{\rm SFR}(\rm z)$ relation inferred from early JWST LF studies. Instead, we find that the evolution in $ρ_{\rm SFR}(\rm z)$ at these very early times is better described by a piece-wise log-linear relation, in which the decline in $ρ_{\rm SFR} (\rm z)$ at $z>12$ is $\simeq4$ times steeper than at redshifts $z < 12$. Our observational results are consistent with a number of theoretical models of galaxy evolution which have incorporated a range of treatments in an attempt to explain the prevalence of UV-bright galaxies at least out to $z \simeq 12$ (e.g., increased star-formation efficiency, stochastic star-formation histories, an evolving stellar initial mass function and/or a shift towards attenuation-free stellar populations). However, our results are also entirely consistent with a relatively simple galaxy evolution model with no such adjustments, in which the rapid evolution of the dark-matter halo mass function at early times is for a while partially masked by progressively younger stellar ages, with the inferred epoch of first galaxy formation lying at $z\simeq15$. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2604_16666 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | A search for the first galaxies across $>0.6$ deg$^2$ of JWST imaging: new evidence for a rapid decline in star-formation activity at $z>12$ McLeod, D. J. Dunlop, J. S. McLure, R. J. Donnan, C. T. Begley, R. Antonogiannaki, S. Magee, D. Illingworth, G. D. Haro, P. Arrabal Bondestam, C. Carnall, A. C. Cullen, F. Dickinson, M. Ellis, R. S. Frye, B. L. Golawska, H. Grogin, N. A. Holst, I. J. B. Kamieneski, P. S. Leung, H. -H. Liu, F. -Y. Stanton, T. M. Tittley, E. R. Astrophysics of Galaxies We present a new determination of the evolving galaxy UV luminosity function (LF) over the extreme redshift range $12.5<z<18.5$, based on a wide-area search of $>$0.6 deg$^2$ of JWST NIRCam imaging containing $>150$ independent sight-lines. We find evidence for an accelerated decline in the UV LF, and hence inferred star-formation rate density ($ρ_{\rm SFR}$), over the $\simeq100\rm{Myr}$ cosmic time interval between $z=11$ and $z=13.5$. Moreover, based on a notable lack of galaxy candidates at $z>14.5$, we find evidence for an even more rapid descent in star-formation activity towards earlier times, with our new measurement of $ρ_{\rm SFR}$ at $z\simeq15.5$ lying significantly below an extrapolation of the log-linear $ρ_{\rm SFR}(\rm z)$ relation inferred from early JWST LF studies. Instead, we find that the evolution in $ρ_{\rm SFR}(\rm z)$ at these very early times is better described by a piece-wise log-linear relation, in which the decline in $ρ_{\rm SFR} (\rm z)$ at $z>12$ is $\simeq4$ times steeper than at redshifts $z < 12$. Our observational results are consistent with a number of theoretical models of galaxy evolution which have incorporated a range of treatments in an attempt to explain the prevalence of UV-bright galaxies at least out to $z \simeq 12$ (e.g., increased star-formation efficiency, stochastic star-formation histories, an evolving stellar initial mass function and/or a shift towards attenuation-free stellar populations). However, our results are also entirely consistent with a relatively simple galaxy evolution model with no such adjustments, in which the rapid evolution of the dark-matter halo mass function at early times is for a while partially masked by progressively younger stellar ages, with the inferred epoch of first galaxy formation lying at $z\simeq15$. |
| title | A search for the first galaxies across $>0.6$ deg$^2$ of JWST imaging: new evidence for a rapid decline in star-formation activity at $z>12$ |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2604.16666 |