arXiv subjects

Chandana Hegde

Publications and source records attributed to Chandana Hegde.

3 recordsLinked to original sources

arXiv2026

Environmental dependence of the Mass-Metallicity Star Formation Relations at z=4-10 with JWST

We study how environment affects the mass-metallicity relation (MZR) at $z=4$-$10$ using deep imaging and spectroscopy from the James Webb Space Telescope (JWST). Combining CEERS and JADES, we compile a sample of 225 galaxies with stellar masses, star-formation rates, and gas-phase metallicities. We characterize environment using the projected fifth-nearest-neighbour surface density, $Σ_{5}$, within $Δz=\pm0.25$. At $4.5<z<7$, we find that galaxies in dense regions are more metal-rich at fixed $M_\star$ by $\sim0.1$-0.2 dex, while the slopes of the MZR remain similar across environments. Including SFR increases the separation, suggesting more efficient chemical enrichment in overdense regions. Compared to the local $T_e$-based FMR, our full sample lies $\simeq0.2$-0.3 dex below the $z\sim0$ relation, with a smaller deficit in overdense environments. We also examine how metallicity relates to galaxy size using NIRCam-based effective radii. Metallicity increases weakly with size up to $R_e\sim1$ kpc and then flattens, with only a modest residual trend at fixed $M_\star$ and little environmental dependence. Using mass-weighted stellar ages at $5<z<10$, we find a positive age-metallicity relation in both environments, steeper in the field. Finally, we find that the star-formation rate density is higher in overdense regions at $z\simeq6$-9 by a factor of $\sim2$-3. Overall, our results suggest that environment accelerates both star formation and chemical enrichment during the epoch of reionization. Future wide-area JWST spectroscopy, combined with ALMA and Euclid, will better constrain the role of environment in early galaxy evolution.

astro-ph.GA↗

arXiv2026

The ionised interstellar medium of DSFGs revealed by JWST/NIRSpec and ALMA: Super-solar metallicity, low ionisation parameters and, typical electron densities

We present a detailed study of near-infrared (2-4$\rm μ$m) JWST/NIRSpec spectra of 48 high-redshift ($z=2.53^{+1.32}_{-0.70}$) galaxies detected with ALMA at $>3σ$. From a multi-wavelength SED analysis we establish the sample has a a median stellar mass of $\rm\log_{10}(M_\ast/M_\odot)=10.8\pm0.1$ and dust mass of $\rm\log_{10}(M_{\rm d}/M_\odot)=8.7\pm0.1$, covering a broad range of far-infrared luminosity $\rm (\log_{10}(L_{FIR}/L_\odot)=10.9-12.7)$. The majority of sources show no signs of AGN activity, with 40% having either X-ray counterparts $(\rm L_{Xc}>10^{42}erg/s)$, elevated optical line ratios, or broad (FWHM>800 km/s) H$α$ profiles, although we note this is a lower limit due to the stochastic placement of NIRSpec slits. We establish the sample has a median gas-phase metallicity of $12+\log({\rm O/H})=8.71\pm0.02$, as derived from the [NII]/H$α$ ratio, with the most FIR-luminous galaxies ($\rm\log_{10}(L_{\rm FIR}/L_\odot)>12$) falling $0.15\pm0.03$dex above the fundamental metallicity relation. From the [SII] emission-line doublet ratio, we measure a median electron density of $\log_{10}(n_{\rm e}/{\rm cm}^{-3})=2.53\pm0.07$ consistent with less-massive, star-forming, galaxies at the same epoch. For nine galaxies with [OII] and H$β$ detections (median $\rm\log_{10}(L_{\rm FIR}/L_\odot)=11.81\pm0.15$), we derive a median observed (dust-uncorrected) ionisation parameter of $\rm\log_{10}(U)=-2.84\pm0.06$. Our results indicate that luminous far-infrared galaxies are massive, chemically evolved systems that appear to deviate from the standard dust and metal production equilibrium observed in less obscured galaxies. This study demonstrates the synergy of JWST and ALMA in unveiling the nature of DSFGs, and highlights the need for a NIRSpec survey of uniformly selected, massive, dust-obscured, galaxies to fully characterise their interstellar medium.

astro-ph.GA↗

arXiv2025

ECOGAL I. Project design and the first catalogue

We present ECOology for Galaxies using ALMA archive and Legacy surveys (ECOGAL), an ALMA data mining project. Using the footprints of the James Webb Space Telescope (JWST) and the Hubble Space Telescope (HST), we query and uniformly reprocess ALMA data to produce continuum images and two complementary source catalogues: (i) a prior-based catalogue anchored to optical/near-infrared detections, and (ii) a blind catalogue based on significant ALMA detections. Detection thresholds are established through peak SNR statistics and analysis of inverted maps. In this paper, we focus on the ALMA-accessible CANDELS fields (COSMOS, GOODS-S, and UDS), covering ~130,000 optical/NIR-selected galaxies spanning $0.0 < z < 15.0$. We identify 1288 detections (622 unique) with optical/NIR counterparts across the two methods, of which 832 detections (395 unique) appear in both. Among the 622 unique sources, 307 have spectroscopic redshifts from $0.12 < z < 6.85$. ECOGAL expands the parameter space previously explored by $A^3COSMOS$ and $A^3GOODS-S$ by incorporating the UDS field and integrating publicly available JWST datasets from the DAWN JWST Archive (DJA). We also highlight several science cases enabled by ECOGAL, including the evolution of cosmic gas and dust masses, obscured star formation and optically dark systems. ECOGAL provides science-ready data sets for the community and showcases the power of combining over a decade of accumulated public data with other legacy datasets. The data product is made publicly available and accompanies a post demonstrating the usage of the catalogue on the DJA webpage.

astro-ph.GA↗