JWST MIRI detections of H$\hat{I}\pm$ and [O III] and direct metallicity measurement of the $z=10.17$ lensed galaxy MACS0647$-$JD

Abstract

JWST spectroscopy has revolutionized our understanding of galaxies in the early universe. Covering wavelengths up to $5.3\hat{\mathrm{I}}¼\mathrm{m}$, NIRSpec can detect rest-frame optical emission lines H$\hat{I}\pm$ out to $z=7$ and [O III] to $z=9.5$. Observing these lines in more distant galaxies requires longer wavelength spectroscopy with MIRI. Here we present MIRI MRS IFU observations of the lensed galaxy merger MACS0647$-$JD at $z=10.165$. With exposure times of 4.2 hours in each of two bands, we detect H$\hat{I}\pm$ at $9\ddot{I}ƒ$, [O III]$\lambda 5008$ at $11\ddot{I}ƒ$, and [O III]$\lambda 4960$ at $3\ddot{I}ƒ$. Combined with previously reported NIRSpec spectroscopy that yields seven emission lines including the auroral line [O III]$\lambda 4363$, we present the first direct metallicity measurement of a $z>10$ galaxy: $12+\log (O/H)=7.79\pm 0.09$, or $0.13_{-0.03}^{+0.02}{Z}_{\odot }$. This is similar to galaxies at $z\sim 4-9$ with direct metallicity measurements, though higher than expected given the high specific star formation rate $\log (sSFR/y{\mathrm{r}}^{-1})=-7.4\pm 0.3$. We further constrain the ionization parameter $\log (U)$ = $-1.9\pm 0.1$, ionizing photon production efficiency $\log (\hat{I}{¾}_{\mathrm{ion}})$ = $25.3\pm 0.1$, and star formation rate $5.0\pm 0.6M_{\odot }/\mathrm{yr}$ within the past $10\mathrm{Myr}$. These observations demonstrate the combined power of JWST NIRSpec and MIRI for studying galaxies in the first $500$ million years.

16 pages, 8 figures, accepted for publication in ApJ