Spatially resolved Halpha and ionizing photon production efficiency in the lensed galaxy MACS1149-JD1 at a redshift of 9.11

Abstract

We present MIRI/JWST medium-resolution spectroscopy (MRS) and imaging (MIRIM) of the lensed galaxy MACS1149-JD1 at a redshift of $z$\,=\,9.1092pm 0.0002, when the Universe was about 530 Myr old. We detect, for the first time, spatially resolved Halpha emission in a galaxy at a redshift above nine. The structure of the Halpha emitting gas consists of two clumps, S and N, carrying about $60<!PCT!>$ and $40<!PCT!>$ of the total flux, respectively. The total Halpha luminosity implies an instantaneous star-formation rate in the range of 3.2\,pm \,0.3 and 5.3\,pm odot $ for sub-solar and solar metallicities. The ionizing photon production efficiency, $ ion )$, shows a spatially resolved structure with values of 25.55\,pm \,0.03; 25.47\,pm \,0.03; and 25.91\,pm $ for the integrated galaxy and clumps S and N, respectively. The Halpha rest-frame equivalent width, EW$_ $\,(Halpha ), is $\,AA for the integrated galaxy, but it presents extreme values of and geq 1951\,AA for clumps S and N, respectively. The spatially resolved ionizing photon production efficiency is within the range of values measured in galaxies at a redshift above six and well above the canonical value (25.2\,pm $). The EW$_ $\,(Halpha ) is a factor of two lower than the predicted value at $z$\,=\,9.11 based on the extrapolation of the evolution of the $\,(Halpha ) with redshifts, propto $, including galaxies detected with JWST. The extreme difference of the EW$_ $\,(Halpha ) for clumps S and N indicates the presence of a recent (<5 Myr) stellar burst in clump N and a star formation over a larger period of time (e.g., sim 50 Myr) in clump S. The different ages of the stellar population place MACS1149-JD1 and clumps N and S at different locations in the log($ ion $) to EW$_ $\,(Halpha ) plane and above the main relation defined from intermediate- and high-redshift (z=3-7) galaxies detected with JWST. Finally, clump S and N show very different Halpha kinematics, with velocity dispersions of 56\,pm $ and 113\,pm $, likely indicating the presence of outflows or increased turbulence in clump N. The dynamical mass $M_ dyn $= (2.4\,pm \,0.5)\,times odot $, obtained from the size of the integrated Halpha ionized nebulae and its velocity dispersion, is within the range previously measured with the spatially resolved OIII 88mu m line.