A combined PRIMER+MINERVA study of the evolution of $\mathbf{[O\mbox{III}]+Hβ}$ equivalent width from $\mathbf{z}=3$ to $\mathbf{z}=8.5$

Abstract

We present an analysis of the evolution of $[OIII]+\mathrm{H}\beta$ equivalent width ($W_{\lambda }$) over the redshift range $z=3$ to $z=8.5$, based on combining the JWST NIRCam PRIMER and MINERVA imaging in the UDS survey field. We find that the combined medium- and broad-band data set reduces the photometric redshift outlier rate to $\eta =4.7\%$ at $m_{F444W}\le 28$, a $42\%$ reduction compared with PRIMER imaging alone. We also demonstrate that the combined data set facilitates the accurate recovery of $[OIII]+\mathrm{H}\beta$ equivalent widths in redshift bins centred on $z\sim 3.2,4.0,5.0,7.2,8.3$; corresponding to the F210M, F250M, F300M, F410M and F460M filters. Based on a final sample of $N=1964$ galaxies with $M_{\mathrm{UV}}\le -19.25$, we first provide new constraints on the bright end of the $z=7-8$ $[OIII]+\mathrm{H}\beta$ luminosity function (${\log }_{10}{\varphi }^{\ast }=-4.3_{-0.5}^{+0.2}$, ${\log }_{10}{L}^{\ast }=-43.4_{-0.2}^{+0.3}$), before proceeding to investigate the redshift evolution of $[OIII]+\mathrm{H}\beta$ equivalent width. Using SED modelling based on non-parametric continuity star-formation histories, we find that the median $[OIII]+\mathrm{H}\beta$ equivalent width monotonically increases with redshift, rising from ${\log }_{10}(W_{\lambda })=2.54_{-0.01}^{+0.01}$ at $z\simeq 3$ to ${\log }_{10}(W_{\lambda })=3.05_{-0.03}^{+0.03}$ at $z\simeq 8$. In tandem, the distribution of ${\log }_{10}(W_{\lambda })$ is observed to become increasingly asymmetric with redshift, producing a fraction of extreme emission-line galaxies (EELGs, $W_{\lambda }>1000$Å) that reaches $f_{\mathrm{EELG}}=0.50\pm 0.10$ by $z=8.3$. Our SED modelling results indicate that the physical driver of this evolution is increasingly bursty star-formation, with EELGs the result of particularly high specific star-formation rates over the 10 Myr prior to observation.

arXiv commentSubmitted to MNRAS, 12 pages, 9 figures