arXiv subjects

Adarsh Ranjan

Publications and source records attributed to Adarsh Ranjan.

6 recordsLinked to original sources

arXiv2026

Unveiling Metal Mixing in a Grand-Design Spiral: A UV-optical multiphase spatially resolved study of M83

We present a spatially resolved, multiphase study of chemical enrichment around young star clusters (YSCs) in the nearby grand-design spiral M83 by combining far-ultraviolet(UV) absorption-line spectroscopy from HST/COS with cospatial optical spectroscopy from VLT/MUSE and LBT/MODS. Our sample includes 18 YSCs spanning spectroscopic ages of ~1-6 Myr and galactocentric radii out to R/R_{25}=0.56. Neutral (H I) abundances were derived from UV absorption-line spectroscopy and compared with ionised (H II) abundances from reddening-corrected optical emission lines. Because auroral lines are not detected in all regions, we develop and apply an empirical multi-zone electron temperature (T_e) calibration based on strong-line diagnostics to estimate T_e and derive reliable nebular abundances. We measure oxygen(O), sulphur(S), nitrogen(N), and iron(Fe) abundance tracing enrichment from distinct nucleosynthetic channels. The alpha-elements (O and S) exhibit similar behaviour, consistent with enrichment by core-collapse supernovae, whereas Fe shows weaker variations, reflecting its delayed production by Type Ia supernovae. Nitrogen displays the largest phase offset (ionised-neutral), with enhancements of up to $Delta$N/H~1.5 dex and $Delta$N/O>1.5 dex in the ionised gas relative to the neutral phase, indicating localised enrichment by massive stars and inefficient mixing between gas phases on Myr timescales. While the ionised gas exhibits signatures of feedback-regulated chemical enrichment and large-scale abundance gradients, corresponding trends are weak or absent in the neutral gas, consistent with metals remaining largely confined to the immediate star-forming environment during the earliest stages of cluster evolution in a massive grand-design spiral.

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arXiv2025

CLASSY XIV: The Nitrogen Exception -- Multi-Phase Enrichment and Feedback in High-$z$ Analogs

We present a first-of-its-kind analysis of the metal content across two interstellar medium (ISM) phases in a sample of 31 local star-forming galaxies from the COS Legacy Archive Spectroscopic SurveY (CLASSY), selected as analogues of high-$z$ systems. Using co-spatial UV absorption and optical emission-line spectroscopy, we compare abundances of N, O, S, and Fe in the low-ionization (neutral) and high-ionization (ionized) gas, providing a multi-phase view of enrichment shortly after the current starburst and over longer timescales when ejecta from previous episodes have cooled and mixed. We find that O and S, produced predominantly in short-lived massive stars, are well mixed between the two phases, with scatter reflecting local inhomogeneities. Fe, predominantly produced by Type Ia supernovae on $\sim$1 Gyr timescales, is higher in the neutral gas, reflecting either delayed mixing of older Fe-enriched material or preferential depletion of Fe from the ionized phase through dust formation in core-collapse supernova ejecta. N exhibits the largest phase offset, with N/H$_{ion}$ systematically $\sim$0.7 dex higher than N/H$_{neu}$, and the magnitude of this offset correlates with stellar mass, metallicity, star-formation rate, and most strongly with the ISM outflow velocity. N/O ratios in the ionized phase rise rapidly within 3-6 Myr relative to the neutral gas, consistent with N enrichment dominated by Wolf-Rayet stars rather than intermediate-mass AGB stars on longer timescales. These results demonstrate that localized stellar feedback, outflows, and phase-dependent mixing collectively regulate the chemical evolution of star-forming galaxies, providing key insight into the extreme N/O abundances recently observed in galaxies at cosmic dawn.

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arXiv2025

The Stellar Morphology & Size of X-ray-selected Active Galactic Nuclei Host Galaxies Revealed by JWST

We investigate the stellar shape and size-mass relationship of X-ray selected Active Galactic Nuclei (AGN) host galaxies using the high-angular resolution and deep sensitivity in the near-infrared of the COSMOS-Web JWST survey field. We present the rest-frame 1-$\mu m$ size, stellar mass, Sersic index, axis-ratio, Gini-$M_{20}$ parameters of 690 moderate luminosity AGNs between redshift 0-3 and with stellar mass $\log M_s\sim 10.75$. We find that AGN host galaxies have an effective radius of 1-5 kpc, which is between star-forming (SFG) and quiescent galaxies (QGs) of the same stellar mass. AGN hosts have similar size-mass trends as SFG and QGs, being smaller at higher redshift for the same stellar mass. The slope of the size-mass relationship of AGN host galaxies is steeper than that of star-forming galaxies. Their rest-frame 1$\mu m$ stellar morphology indicates a significant spheroidal component. We observed a low merger fraction (6%) in our sample as well as substructures similar to disks, bars, and spiral arms in the residual images, which are in tension with evolutionary pathways that require major mergers. However, it may also be due to the different timescales between mergers and AGN activity.

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arXiv2025

Unveiling a Population of Strong Galaxy-Galaxy Lensed Faint Dusty Star-Forming Galaxies

The measurements of the number density of galaxy-galaxy strong lenses can be used to put statistical constraints on the foreground mass distributions. Dusty galaxies uncovered in submillimeter surveys are particularly useful in this regard because of the large volume probed by these surveys. Previous discoveries of strong galaxy-galaxy lensed dusty galaxies are predominantly the brightest in the sky discovered by Herschel, SPT, and Planck. However, models have also predicted a non-negligible fraction of strong galaxy-galaxy lensed faint dusty galaxies, which were difficult to confirm due to technical difficulties. Utilizing the deepest SCUBA-2 submillimeter survey, STUDIES, in both the COSMOS and the UDS fields, together with a red JWST color selection method, we discover a population of 13 strong galaxy-galaxy lensed faint dusty galaxies. The rich ancillary data allow us to confirm their strongly lensed nature via estimates of redshifts and lens modeling. Our systematic search has allowed us to construct the 450$\mu$m number counts of strongly lensed sources down to the flux levels about an order of magnitude fainter than previous measurements. The measured lensing fractions of $\sim$1% are consistent with predictions from models that also successfully produce the number density of the strong galaxy-galaxy lensed bright dusty galaxies. Future searches from Euclid and Roman are expected to discover orders of magnitude more strongly lensed faint dusty galaxies.

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arXiv2024

Model independent approach for calculating galaxy rotation curves for low $S/N$ MaNGA galaxies

Internal kinematics of galaxies, traced through the stellar rotation curve or two dimensional velocity map, carry important information on galactic structure and dark matter. With upcoming surveys, the velocity map may play a key role in the development of kinematic lensing as an astrophysical probe. We improve techniques for extracting velocity information from integral field spectroscopy at low signal-to-noise ($S/N$), without a template, and demonstrate substantial advantages over the standard Penalized PiXel-Fitting method (pPXF) approach. Robust rotation curves can be derived down to $S/N\approx 2$ using our method.

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arXiv2024

Distribution of merging and post-merging galaxies in nearby galaxy clusters

We study the incidence and spatial distribution of galaxies that are currently undergoing gravitational merging (M) or that have signs of a post merger (PM) in six galaxy clusters (A754, A2399, A2670, A3558, A3562, and A3716) within the redshift range, 0.05$\lesssim$$z$$\lesssim$0.08. To this aim, we obtained Dark Energy Camera (DECam) mosaics in $u^{\prime}$, $g^{\prime}$, and $r^{\prime}$-bands covering up to $3\times R_{200}$ of the clusters, reaching 28 mag/arcsec$^2$ surface brightness limits. We visually inspect $u^{\prime}$$g^{\prime}$$r^{\prime}$ color-composite images of volume-limited ($M_r < -20$) cluster-member galaxies to identify whether galaxies are of M or PM types. We find 4% M-type and 7% PM-type galaxies in the galaxy clusters studied. By adding spectroscopic data and studying the projected phase space diagram (PPSD) of the projected clustocentric radius and the line-of-sight velocity, we find that PM-type galaxies are more virialized than M-type galaxies, having 1--5% point higher fraction within the escape-velocity region, while the fraction of M-type was $\sim$10% point higher than PM-type in the intermediate environment. Similarly, on a substructure analysis, M types were found in the outskirt groups, while PM types populated groups in ubiquitous regions of the PPSD. Adopting literature-derived dynamical state indicator values, we observed a higher abundance of M types in dynamically relaxed clusters. This finding suggests that galaxies displaying post-merging features within clusters likely merged in low-velocity environments, including cluster outskirts and dynamically relaxed clusters.

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