Tiny Galaxies, Mighty Nitrogen: Linking Chemical Anomalies to Compact Galaxies at High Redshift using JWST/JADES

Abstract

The origin of anomalous chemical enrichment in high-redshift galaxies discovered by JWST remains a key question in galaxy evolution. Enhanced nitrogen abundances have been identified in several galaxies at early cosmic times, but the physical conditions driving this enrichment, and their connection to galaxy morphology, remain unclear. We test whether morphologically compact galaxies at 4 < z < 7 show stronger chemical anomalies than extended systems. Using JWST/NIRSpec spectroscopic data, we construct samples of compact and extended galaxies and analyse their rest-frame spectra. We stack the spectra of each population and measure key UV and optical emission lines. We detect nitrogen emission in the compact galaxy stack, including NIV], and [NII], while also detecting key carbon and oxygen lines. The detection of [OIII]λ4363 enables a direct-Te determination of the oxygen abundance. From these measurements, we infer chemical abundance ratios, including log(N/O) and log(C/O). We find that compact galaxies exhibit elevated log(N/O) (by ~ 0.7 dex) and log(C/O) (by ~ 0.5 dex) abundance ratios relative to extended systems. The abundance patterns of compact galaxy stacks are comparable to those of previously identified individual nitrogen-enhanced galaxies at high redshift and second-generation globular-cluster stars in the Milky Way. These results suggest a possible link between galaxy compactness and chemical enrichment pathways in the early Universe. Deeper JWST NIRSpec IFU observations of compact high-redshift galaxies will be crucial for determining the origin, spatial distribution, and evolutionary significance of these abundance patterns.