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Raunaq Singh Rai

Publications and source records attributed to Raunaq Singh Rai.

2 recordsLinked to original sources
arXiv2026

Precise C-N-O Abundances of Individual Galaxies in the First Billion Years from Ultra-Deep, Rest-UV-to-Optical JWST Spectroscopy

We present ultra-deep JWST/NIRSpec $R\sim1000$ spectroscopy of nine star-forming galaxies at $z=6.0-8.3$ in the GOODS-N field, drawn from the Origins of Metal Enrichment in Galaxies at cosmic dAwn (OMEGA) survey. Paired with ancillary ultra-deep G140M observations, the G395M integrations from OMEGA yield continuous rest-frame UV-to-optical coverage and the full suite of diagnostics needed for precise characterisations and measures of the chemical abundances of these systems. Crucially, the auroral [O\,{\scriptsize III}]\,$λ$4363 line is detected in every galaxy, enabling the determination of electron temperatures and direct oxygen abundances of $12+\log(\mathrm{O/H})=7.14-8.18$, independent of strong-line calibrations that dominate systematics at these redshifts. We couple direct oxygen abundances with measurements of rest-frame UV emission-line strengths and ratios to infer the physical properties of our sample. Most importantly, we trace the relationship between oxygen abundance and both C/O and N/O abundance ratios with high fidelity, demonstrating robustly that $z=6.0-8.3$ galaxies follow the local trend in C/O vs. O/H, and that inferences regarding N/O are sensitive to the choice of rest-frame UV (\niv] or \niii]) or optical ([\nii]) tracers. This pilot study demonstrates the power of combining ultra-deep JWST/NIRSpec $R\sim1000$ rest-frame UV and optical spectroscopy, which now requires statistical samples to uncover the nebular properties of the full population of $z\geq 6$ star-forming galaxies.

astro-ph.GA↗
arXiv2026

Unveiling and Characterising Ubiquitous Nitrogen Enhancement in $6 \leq z \leq 10$ Galaxies with JWST Spectroscopy

The James Webb Space Telescope (JWST) has revealed a growing number of $z>6$ galaxies with enhanced N/O ratios that challenge standard chemical enrichment frameworks. We test whether this is exclusive to extreme systems or a generic feature of $6 \leq z \leq 10$ populations through a stacking analysis of 135 galaxies with JWST/NIRSpec $R\sim1000$ spectroscopy, probing the origin of N, C and O enrichment and its dependence on recent star formation. A full-sample composite reveals prominent C III], C IV, N IV] and He II emission, demonstrating a ubiquity of high-ionisation UV lines. Auroral [O III]$λ$4363 electron temperatures and multi-ionisation zone modelling yield direct-$T_e$ abundances with supersolar $\log(\mathrm{N/O}) = -0.57^{+0.09}_{-0.10}$ and subsolar $\log(\mathrm{C/O}) = -0.80^{+0.03}_{-0.03}$ at $12 + \log(\mathrm{O/H}) = 7.79^{+0.03}_{-0.03}$, in contrast with local samples and suggesting significant nitrogen enhancement within the first billion years. Stacking further by recent star formation activity over burst timescales of $Δt = 3$--$20$~Myr, we find that sources caught in a recent burst are less enriched in both N/O and metallicity than those in a relative lull, with the largest contrasts confined to the shortest timescales. C/O, however, remains largely invariant across all metrics. We interpret these observations as the result of delayed AGB enrichment across multiple burst episodes, together with dilution by pristine gas inflows. Cosmological simulations reproduce this trend with CCSNe and AGB yields alone, without the need for shorter-lived (super-)massive stars. Enhanced N/O therefore appears to be a generic feature of high-redshift systems, produced by standard enrichment processes rather than requiring new physical frameworks.

astro-ph.GA↗