Connecting JWST discovered N/O-enhanced galaxies to globular clusters: Evidence from chemical imprints

TL;DR

The paper investigates whether high-redshift NOEGs share chemical fingerprints with Milky Way globular clusters, testing a proto-cluster formation scenario. By compiling 21 NOEGs across $0 ightarrow12$ and comparing their $N/O$, $O/H$, $C/O$, $Fe/O$, and $Y$ with MW GC and NSC stars, the authors find GC-like patterns—especially for 2G GC stars—at low metallicities, and generally subsolar $C/O$ with occasional NSC-like enhancements. They also discuss measurement systematics and environmental conditions, arguing that NOEGs reside in dense, cluster-friendly environments (high $ m obreaksim obreaksim$) with frequent compact star formation and occasional AGN activity, which may be linked to GC formation pathways. The results support a picture in which cluster-dominated star formation in the early universe leaves lasting chemical imprints that survive to today as GC abundance patterns, with NSCs possibly playing a role in some NOEGs. Future high-resolution, spatially resolved abundance maps across NOEGs and their clustered substructures will be essential to robustly connect NOEGs and globular clusters.

Abstract

Recent JWST observations have revealed a growing population of galaxies at $z>4$ with elevated nitrogen-to-oxygen ratios. These "N/O-enhanced" galaxies (NOEGs) exhibit near- to super-solar N/O at sub-solar O/H, clearly deviating from the well-established scaling relation between N/O and O/H observed in local galaxies. The origin of this abundance anomaly is unclear. Interestingly, local globular clusters also exhibit anomalous light-element abundances, whose origin remains debated. In this work, we compare the chemical abundance patterns of 22 known NOEGs at $0\lesssim z\lesssim 12$ -- primarily discovered with JWST -- to those observed in local globular clusters. We find similarities in the abundances of C, N, O, Fe, and He between the two populations. The similar abundance patterns support the scenario in which globular cluster stars formed within proto-cluster environments -- similar to those traced by NOEGs -- that were self-enriched. Indeed, the enhancement in N/O in early galaxies appears to be only found in dense stellar environments with $Σ_{\star}\gtrsim 10^{2.5}~M_\odot~{\rm pc^{-2}}$, as expected for the progenitors of globular clusters in the Milky Way, and similar to those of star clusters identified in strongly lensed high-redshift galaxies. Furthermore, we find a tentative positive correlation between N/O ratios and stellar mass among NOEGs. The apparent high occurrence rate of NOEGs at high redshift is consistent with the picture of cluster-dominated star formation during the early stages of galaxy evolution. Measuring chemical abundances across diverse stellar environments in high-redshift galaxies will be crucial for elucidating the connection between NOEGs and globular clusters.

Figures (9)

• Figure 1: Global properties of high-$z$ NOEGs in our sample. Left: size-stellar mass relation for NOEGs and a compilation of JWST galaxies at photometric redshift of $5<z_{\rm photo}<14$ studied by Morishita_2024. For the JWST sample, Morishita_2024 fitted the redshift evolution of the relation with the parameter $\alpha_z=-0.44$, which we use to normalize $R_e$. We plot the best-fit linear model of Morishita_2024 as the dashed orange line together with the $1\sigma$ dispersion in $\log R_e$ indicated by the shaded region. The NOEGs are generally more compact compared to galaxies at similar stellar masses. Right: stellar mass-redshift relation for NOEGs and JADES photometric sample at $3<z_{\rm photo}<9$. The JADES sample has a $90\%$ completeness at $M_\star \gtrsim 10^{7.5}~M_\odot$ as indicated by the dashed white line Simmonds_2024. The dotted yellow line represents the median trend of the JADES photometric sample and the shaded region is bounded by the 10 percentile and 90 percentile lines. The dash-dotted red line represents the median trend of the JADES subsample with spectroscopic observations and the shaded region is bounded by the 10 percentile and 90 percentile lines. The NOEGs are relatively massive, and their selection is highly inhomogeneous and probably biased by their UV brightness, which allows for measurements of faint nitrogen lines.
• Figure 2: Distributions of NOEGs in the N/O versus O/H space in comparison with local galaxies and stars. Derived abundances for NOEGs come from castellano2024cameron2023cameron_gs9422_2024curti_gsz9_2024schaerer_gnz9_2024isobe2023larson_ceersagn_2023topping2024Topping_2025ji2024ubler2023apascale_sbarc_2023james2009Arellano-cordova_nloud_2024napolitano_ghz9agn_2024Navarro-Carrera_nloud_2024Stiavelli_nloud_2024Zhangyechi_2025 and also this work. Systems showing two abundances connected by dashed lines have their higher abundances derived for high-density components ($n_{\rm e}\gtrsim 10^5~{\rm cm^{-3}}$) decomposed from the observed spectra, and their lower abundances derived for low-density components ($n_{\rm e}< 10^4~{\rm cm^{-3}}$). Derived abundances for local galaxies come from izotov2006pilyugin2012Annibali_2019Grossi_2025. The contours correspond to probability distributions of abundances of MW stars compiled from sdss_dr17 computed by the kernel density estimation function kdeplot from the python package seaborn. Five contour levels are plotted corresponding to 5, 16, 50, 84, and 95 percentiles of the distributions, respectively. Top: abundance patterns of non-GC stars in the MW, where stars with $\log g<1.5$, $\log g>3$, or $T_{\rm eff}>5300$ K are excluded. Stars with azimuthal velocities of $v_{\rm t} \geq 150~{\rm km~s^{-1}}$ trace the thin disk and have an overall higher N/O, which are plotted as green contours with dashed boundaries. The cyan shaded region represents the median trend of MW field stars with no error cut in abundances (selected with $\rm 1.5< \log g < 3$, $T_{\rm eff}<5300$ K, and $v_{\rm t}<150$$\rm km~s^{-1}$) with $1\sigma$ median uncertainties. Bottom: abundance patterns of GC stars (excluding NSC stars) in the MW divided into $\rm 1^{st}$ and $\rm 2^{nd}$ generations. The abundance patterns of stars in the GC 47 Tuc are plotted as purple contours with dashed boundaries. Overall, the abundances of NOEGs are more consistent with those of GC stars, among which the $\rm 2^{nd}$-generation GC stars better overlap with NOEGs at $\rm \log(N/O)>-0.5$.
• Figure 3: Distributions of NOEGs in the C/O versus O/H space in comparison with local galaxies and stars. Derived abundances for NOEGs come from castellano2024cameron2023cameron_gs9422_2024curti_gsz9_2024schaerer_gnz9_2024isobe2023larson_ceersagn_2023topping2024Topping_2025ji2024ubler2023apascale_sbarc_2023Marques-Chaves_2024Arellano-cordova_nloud_2024Navarro-Carrera_nloud_2024napolitano_ghz9agn_2024 and also this work. Derived abundances for local galaxies come from berg_2016berg2019. The contours correspond to probability distributions of abundances of MW stars compiled from sdss_dr17 computed by the kernel density estimation function kdeplot from the python package seaborn. Five contour levels are plotted corresponding to 5, 16, 50, 84, and 95 percentiles of the distributions, respectively. Top: abundance patterns of non-GC stars in the MW, where stars lying on the thin disk and stars with $\log g<1.5$, $\log g>3$, or $T_{\rm eff}>5300$ K are excluded. Stars with azimuthal velocities of $v_{\rm t} \geq 150~{\rm km~s^{-1}}$ trace the thin disk and have an overall higher C/O, which are plotted as green contours with dashed boundaries. The cyan shaded region represents the median trend of MW field stars with $1\sigma$ median uncertainties. Bottom: abundance patterns of GC stars (excluding NSC stars) in the MW divided into $\rm 1^{st}$ and $\rm 2^{nd}$ generations. While NOEGs appear to overlap with the low-metallicity tail of the non-GC stars, they better overlap with GC stars.
• Figure 4: Distributions of NOEGs in the Fe/O versus O/H space in comparison with local galaxies and stars. Derived abundances for NOEGs come from cameron2023cameron_gs9422_2024Nakane_gnz11_2024Nakane_2025ji_gnz11_2024ji2024ubler2023awelch_sba_2024 and also this work. Derived abundances for local galaxies and H ii regions from mendezdelgado_feo_2024 are plotted as open circles, which reach $\rm log(Fe/O)\sim -3$ outside the range shown in the current figure. The horizontal dash-dotted cyan line is the asymptotic line of Fe/O for local galaxies and H ii regions derived by mendezdelgado_feo_2024. The contours correspond to probability distributions of abundances of GC stars compiled from sdss_dr17 computed by the kernel density estimation function kdeplot from the Python package seaborn. Five contour levels are plotted corresponding to 5, 16, 50, 84, and 95 percentiles of the distributions, respectively. Top: abundance patterns of non-GC stars in the MW, where stars lying on the thin disk and stars with $\log g<1.5$, $\log g>3$, or $T_{\rm eff}>5300$ K are excluded. Stars with azimuthal velocities of $v_{\rm t} \geq 150~{\rm km~s^{-1}}$ trace the thin disk and have an overall higher Fe/O, which are plotted as green contours with dashed boundaries. The cyan shaded region represents the median trend of MW field stars with $1\sigma$ median uncertainties. Bottom: abundance patterns of GC stars (excluding NSC stars) in the MW divided into $\rm 1^{st}$ and $\rm 2^{nd}$ generations. While some NOEGs appear to overlap with the low-metallicity tail of the non-GC stars, they also overlap with GC stars.
• Figure 5: Left: Distributions of NOEGs in the Y (i.e., mass fraction of He) versus O/H space in comparison with local galaxies and stars. Derived abundances for the LyC of the Sunburst Arc come from welch_sba_2024. Derived abundances for GS_9422, RXCJ2248-ID, and GLASS_150008 come from yanagisawa_he_2024. For GN-z11, A1703-zd6, GS_3073, ID60001, and Mrk 996, we derived their He abundances based on the measurements of He i and He ii emission lines. In comparison, we also plot 1) Y as a function of O/H for local galaxies fitted by dopita2006 and Matsumoto2022, and 2) maximum Y enhancement in individual MW GCs as a function of O/H averaged over the 2G stars. Middle: distributions of Y for a sample of local GC stars measured by milone_hegc_2018. Right: maximum enhancement in Y (see text) for a sample of local GC stars versus the inferred initial masses of the GCs measured by milone_hegc_2018, where accreted NSCs of previous dwarf galaxies are marked as star symbols. The NOEGs show a tentative trend of decreasing Y with increasing metallicity, which might be connected to the masses of clusters formed in these systems or caused by the bias in deriving Y (see text for details).