arXiv subjects

Arghyadeep Basu

Publications and source records attributed to Arghyadeep Basu.

14 recordsLinked to original sources

arXiv2026

A Glimpse of the Low-Mass End of the Direct Mass-Metallicity Relation at $z\sim6-8$

The competition between metal synthesis and feedback from massive stars establishes the mass-metallicity relation (MZR) at low-redshifts. Examining this relation at higher redshifts, particularly at the low-mass end $\lesssim10^{8}\,{\rm M_\odot}$, is essential for understanding chemical enrichment and stellar feedback. In this study, we utilize the deep ($\sim30\,$hrs) JWST/NIRSpec G395M GLIMPSE-D survey of the lensed field Abell S1063, to explore the low-mass end of the MZR at high redshift ($z\sim6-8$). We identify eight [OIII]$\lambda$4364 emitters, enabling the most reliable "direct" metallicity measurements in galaxies down to stellar masses of $\sim10^{6-8}\,{\rm M_\odot}$. By combining our sample and galaxies with [OIII]$\lambda$4364 detections from the literature, we calculate direct metallicities for 21 galaxies. We compare our direct metallicities to those derived from strong-line diagnostics, and find them to be consistent with previous calibrations. We fit the MZR at $10^{6.7-9}\,M_{\odot}$ with $\sim0.3-0.5$ dex lower metallicity than local galaxies at similar stellar mass. We find the slope to be $0.25\pm0.10$, comparable to the local MZR; and the MZR exhibits a scatter of $\sim0.2\,$dex, which is larger than the local MZR, The lower metallicities may reflect denser, more gas-rich early environments, with continuous inflow of metal-poor gas diluting the ISM metallicity. In addition, we show that in extremely high electron densities ($n_e \gtrsim 10^5\,{\rm cm^{-3}}$), metallicities can be significantly underestimated ($\sim0.5$ dex), if lower $n_e$ are assumed for galaxies with high $n_e$. In a nutshell, these observations provide the first glimpse of the low-mass MZR at $z\sim6-8$ using direct metallicity measurements. More deep spectroscopic observations in lensed fields will be critical to robustly characterize the MZR and chemical evolution in the early universe.

astro-ph.GA↗

arXiv2026

A GLIMPSE of the 99%: a census of the faintest galaxies during the epoch of reionization and its implications for galaxy formation models

We present a comprehensive study of the galaxy UV luminosity function (UVLF) at $z=6-9$ leveraging deep JWST observations from the GLIMPSE survey. Thanks to gravitational lensing, we probe the UVLF to an unprecedented depth of $M_{\text{UV}} = -12$ mag, approximately three magnitudes deeper than previous robust constraints. Our UVLF determination incorporates a rigorous end-to-end uncertainty framework, including statistical and systematic lensing uncertainties. We find that the $z \sim 7$ UVLF continues to rise steeply with a faint-end slope of $\alpha = -1.98_{-0.05}^{+0.06}$. Crucially, our data show no clear evidence of a turnover down to \muv $= -12.3$. The persistence of this faint population provides stringent constraints on galaxy formation models and cosmological simulations that predict an early flattening of the luminosity function due to radiative feedback or star-formation thresholds. Furthermore, post-JWST models specifically calibrated to match the UV-bright excess at $z > 10$ generally fail to reproduce the observed evolution toward lower redshifts and fainter magnitudes, highlighting a significant tension in our current understanding of early galaxy assembly. We derive a comoving ionizing emissivity at $z=7$ of log($n_{\mathrm ion}$ / s$^{-1}$ Mpc$^{-3}$) $\approx 50.85$, which suggests that faint galaxies dominate the ionizing budget, providing enough photons to maintain reionization even in a highly clumped IGM ($C_{\text{HII}} = 5$). As our detection of faint galaxies effectively rules out a luminosity function truncation at $M_{\text{UV}} \geq -15$, these results emphasize the need to either accurately characterize the ionizing properties of the global, low-mass galaxy population at $z > 6$, or to refine physical models of intergalactic medium clumping and its redshift evolution to maintain consistency with the observed reionization timeline.

astro-ph.GA↗

arXiv2026

GLIMPSED: Direct evidence for a fast AGN-driven outflow from a z=6.64 Little Red Dot host galaxy

We report the discovery of GLIMPSED-329380, a z=6.64 galaxy behind Abell S1063, which shows signs of an extreme ionised outflow driven by an active galactic nucleus (AGN). The deep JWST/NIRSpec medium grating observations show spatially resolved structures of a host galaxy containing the very fast outflow and an AGN, which we analyse separately. The outflow, mainly traced by broad [O III]{\lambda}5008 and H{\alpha} emissions in the host, reaches a full-width half-maximum velocity of ~5500km/s, velocities only observed in AGN-dominated systems. From the Balmer decrement, we observe that while the narrow emission lines show no dust attenuation, the outflowing gas is dusty. We use emission lines diagnostics to infer gas abundances within the host galaxy. The oxygen abundance is 12+log(O/H) ~ 7.95 (~18% solar) and the host is slightly nitrogen-enriched with log(N/O) ~ -0.75. Despite its extreme velocity, the mass loading factor (<0.1) and the kinematic energy of the outflow (~10^43 erg/s) suggest limited impact on star formation. The AGN component shows many similarities with little red dots (LRDs): a characteristic "V-shape", exponential profile in hydrogen lines, numerous detection of forbidden [Fe II] lines, a Balmer break, and a broad absorption feature at ~4550 {\AA}. This detection of a fast outflow in an LRD, rare in surveys dominated by low-resolution (e.g. PRISM) spectra, provides direct evidence of AGN activity in these systems.

astro-ph.GA↗

arXiv2026

A GLIMPSE into the UV Continuum Slopes of the Faintest Galaxies in the Epoch of Reionization

As observations have yet to constrain the ionizing properties of the faintest (M$_{\rm UV}$ > -16) galaxies, their contribution to cosmic reionization remains unclear. The rest-frame ultraviolet (UV) continuum slope ($\beta$) is a powerful diagnostic of stellar populations and one of the few feasible indicators of the escape fraction of ionizing photons (f$_{\rm esc}$) for such faint galaxies at high-redshift. Leveraging ultra-deep JWST/NIRCam GLIMPSE imaging of strong lensing field Abell S1063, we estimate UV continuum slopes of 555 galaxies at z $>$ 6 with absolute magnitudes down to M$_{\rm UV}$ $\simeq -$12.5. We find a modest evolution of $\beta$ with redshift and a flattening in the $\beta$-M$_{\rm UV}$ relation such that galaxies fainter than M$_{\rm UV}$ $\sim -$16.5 no longer exhibit the bluest UV slopes. The 138 ultra-faint galaxies with M$_{\rm UV}$ $> -$16 are a diverse population encompassing dusty (30\%), old (15\%), and low-mass (50\%) galaxies. We apply the empirical $\beta$-f$_{\rm esc}$ relation from local Lyman continuum leakers, finding the mean f$_{\rm esc}$ peaks at $\sim 20\%$ at M$_{\rm UV}=-$16.5 and declines towards fainter galaxies, while remaining consistent with f$_{\rm esc}$ = 14\% within uncertainties, in agreement with recent radiative transfer simulations. Incorporating GLIMPSE constraints on the UV luminosity function, ionizing photon production efficiency, and escape fractions produces a reionization history consistent with independent observational constraints. Our results indicate galaxies with M$_{\rm UV}$ between $-18$ and $-14$ supplied $\sim 60\%$ of the ionizing photons to cosmic reionization, while the lower f$_{\rm esc}$ of fainter galaxies produces a natural cutoff in the ionizing photon production rate density.

astro-ph.GA↗

arXiv2026

GLIMPSE-DDT spectroscopic properties of faint-end galaxies at $z\sim6$: Towards first metal enrichment, dust production, and ionizing photon production

Ultra-faint galaxies at high-$z$ are fundamental elements of the early galaxy assembly, and spectroscopic characterization of this population is essential to understand the earliest galaxy evolution. Leveraging the ultra-deep JWST/NIRCam and NIRSpec observations of a gravitational lensing field of Abell S1063, taken as part of the GLIMPSE survey, we present spectroscopic properties of 16 galaxies fainter than $M_{\rm UV}=-17$ mag, including the metallicity, dust attenuation, and the ionizing photon production efficiency. The emission lines are generally quite strong, roughly half of which cannot be replicated with standard stellar populations and require an extreme ionizing source. We also identify relatively strong [OIII] emission lines from all sample galaxies, which indicates that the low-mass end of the mass-metallicity relation is extended down to $M_\star\sim10^6\ M_\odot$ at $z\sim6$. The strong [OIII] line detection from the lowest-mass galaxy among the sample ($M_\star\sim10^{5.6}\ M_\odot$) stands in contrast to recent reports of extremely metal-poor galaxy candidates at similar mass and redshift, suggesting that there could be two distinct pathways of the earliest metal enrichment as simulations have predicted. Interestingly, we detect both dust attenuation and galactic outflow in one of the sample galaxies with $M_\star=10^{6.6}\ M_\odot$ at $z=5.5$. All the dust, metal, and outflow contents in this galaxy can be consistently explained by supernovae (SNe), indicative of the key roles of SNe in the earliest galaxy assembly such as dust production, metal enrichment, stellar feedback, and baryon cycle.

astro-ph.GA↗

arXiv2026

GLIMPSE-D: Metallicity Decline in Faint Galaxies: Implications for [O III]+Hb Luminosity Function and Reionisation Budget

We report the measurement of the R3=[O III]5008/Hb ratios for 54 galaxies in the GLIMPSE-D survey. Thanks to gravitational lensing, our sample includes galaxies with -20 < Muv < -14 at z=6-9. We derive oxygen abundances using calibrated relationships. We observe a significant decline in R3 values below Muv > -18, which we interpret as evidence of decreasing metallicities in fainter regimes. We explore four prescription models of the evolution of R3 with UV emission based on the new measurements and results from previous surveys. Applying these models to the GLIMPSE [O III]+Hb luminosity functions, we measure and extrapolate the ionising photon production rate $\dot{N}_{ion}$ of galaxies down to very faint limits SFR(Ha) > 5e-3 Msun/yr. Our results support the dominant contribution of star-forming galaxies to reionisation, and are consistent with the recent discovery of ultra-faint metal-poor galaxies. Our measurements of the relative contribution of each luminosity bin show that galaxies with L(Ha)~1e41 to 1e42 erg/s dominate at 8<z<9, but the relative contributions become more uniform at $7<z<8$. Extreme models either under- or over-estimate the ionising photon budget, while intermediate models align with recent observational constraints.

astro-ph.GA↗

arXiv2025

JWST's GLIMPSE: an overview of the deepest probe of early galaxy formation and cosmic reionization

We present an overview of the JWST GLIMPSE program, highlighting its survey design, primary science goals, gravitational lensing models, and first results. GLIMPSE provides ultra-deep JWST/NIRCam imaging across seven broadband filters (F090W, F115W, F200W, F277W, F356W, F444W) and two medium-band filters (F410M, F480M), with exposure times ranging from 20 to 40 hours per filter. This yields a 5$\sigma$ limiting magnitude of 30.9 AB (measured in a 0.2 arcsec diameter aperture). The field is supported by extensive ancillary data, including deep HST imaging from the Hubble Frontier Fields program, VLT/MUSE spectroscopy, and deep JWST/NIRSpec medium-resolution multi-object spectroscopy. Exploiting the strong gravitational lensing of the galaxy cluster Abell S1063, GLIMPSE probes intrinsic depths beyond 33 AB magnitudes and covers an effective source-plane area of approximately 4.4 arcmin$^2$ at $z \sim 6$. The program's central aim is to constrain the abundance of the faintest galaxies from $z \sim 6$ up to the highest redshifts, providing crucial benchmarks for galaxy formation models, which have so far been tested primarily on relatively bright systems. We present an initial sample of $\sim 540$ galaxy candidates identified at $6 < z < 16$, with intrinsic UV magnitudes spanning $M_{\mathrm UV}$ = $-$20 to $-$12. This enables unprecedented constraints on the extreme faint end of the UV luminosity function at these epochs. In addition, GLIMPSE opens new windows for spatially resolved studies of star clusters in early galaxies and the detection and characterization of faint high-$z$ active galactic nuclei. This paper accompanies the first public data release, which includes reduced JWST and HST mosaics, photometric catalogs, and gravitational lensing models.

astro-ph.GA↗

arXiv2025

Tracing The Start and End of Cosmic Reionization -- Exploring The Role of Ionizing Sources as drivers

This thesis investigates the Epoch of Cosmic Reionization (EoR), a key period in the early Universe when the first luminous sources formed and their radiation transformed the intergalactic medium (IGM) from neutral to ionized. Understanding this process reveals how the first stars and galaxies formed, influenced their surroundings, and shaped large-scale structures. The work traces both hydrogen and helium reionization by identifying the sources that produced ionizing radiation and examining how this radiation affected the thermal and ionization history of the IGM. Using the SPICE cosmological radiation-hydrodynamics simulations, the first part analyzes the ultraviolet luminosity function (UVLF) of high-redshift galaxies. It shows that different supernova feedback models drive distinct UVLF variability across mass and redshift, potentially alleviating the bright-galaxy tension seen by JWST. The second part explores how spectra from ionizing sources i.e. single and binary stars, X-ray binaries, emission from the interstellar medium, and active galactic nuclei impact the timing, topology, and thermal history of hydrogen reionization and the Lyman-alpha forest. At lower redshifts, radiative-transfer simulations reveal how helium reionization driven by quasars progressed and how the timing and temperature of the IGM relate to quasar luminosity functions and He II Ly-alpha observations. Finally, predictions for the 3.5 cm hyperfine transition of singly ionized helium-3 offer a novel probe of the post-reionization IGM. Together, these studies combine galaxy formation, radiative processes, and IGM evolution to provide a coherent picture of cosmic reionization and its observable signatures.

astro-ph.GA↗

arXiv2025

Probing Helium Reionization Through the $^{3}\mathrm{He}^{+}$ Hyperfine Transition Line

We investigate the hyperfine transition of $^{3}\mathrm{He}^{+}$ as a promising probe of the IGM during the final stages of helium reionization. Utilising the most recent helium reionization simulation, we generate three-dimensional maps of the 3.5cm ($8.67$ GHz) differential brightness temperature and analyze its evolution. Our results show that the volume-averaged brightness temperature declines rapidly from $\sim 1 \mu$K at $z = 4$ to $\sim 2.5 \times 10^{-3} \mu$K by $z = 2.3$, tracing the HeII to HeIII transition driven by quasars. The power spectrum of the 3.5cm signal exhibits a scale-dependent evolution, peaking on small scales and declining as reionization progresses. We explore the cross-correlation of the 3.5cm transition line with the distribution of AGNs, which shows a transition from positive to negative correlation as ionized regions grow. We also examine the 3.5cm forest and demonstrate that absorption features persist down to $z \sim 2.90$, even when more than $85\%$ of HeII is ionized. Although current observational upper limits lie several orders of magnitude above theoretical predictions, future radio arrays such as $\mathrm{SKA-mid}$ offer promising prospects. Overall, this study highlights the $^{3}\mathrm{He}^{+}$ hyperfine transition as a sensitive tracer of the thermal and ionization history of the IGM during helium reionization.

astro-ph.CO↗

arXiv2025

Influence of the Spectral Energy Distribution of Reionization-Era Sources on the Lyman-$\alpha$ Forest

Interpreting Lyman-$\alpha$ forest properties during the epoch of reionization requires assumptions about the spectral energy distribution (SED) of ionizing sources. These are often simplified to blackbody or power-law spectra, potentially overlooking contributions from high-energy processes. In this work, we investigate how different SED models of reionization-era sources shape the thermal and ionization state of the intergalactic medium (IGM) and imprint on the Ly$\alpha$ forest during the late stages of reionization. We perform $3D$ radiative transfer simulations with CRASH, post-processed on Sherwood-type hydrodynamical outputs, exploring both physically motivated SEDs including X-ray binaries, Bremsstrahlung from shock-heated interstellar medium, and binary stars and idealized blackbody and power-law spectra. While the large-scale morphology of ionized regions is broadly similar across all models, harder spectral components extend partially ionized zones, produce larger He III regions, and heat the surrounding IGM. By adopting simplified spectra there is the risk of underestimating the contribution of high-energy sources, which for most models we consider are found to alter the effective optical depth, the flux power, and the local transmissivity within the current $\sim 1 \sigma$ measurement uncertainties. The differences across models are most pronounced in the behavior of the proximity zone and in the power at intermediate scales, offering the most promising diagnostics to disentangle source populations. With upcoming high precision measurements from ELT and DESI, realistic SED modelling will be essential for robustly connecting Ly$\alpha$ forest observations to the sources driving the end of reionization.

astro-ph.GA↗

arXiv2025

Variability of the UV luminosity function with SPICE

We investigate the variability of the UV luminosity function (UVLF) at $z > 5$ using the SPICE suite of cosmological, radiation-hydrodynamic simulations, which include three distinct supernova (SN) feedback models: bursty-sn, smooth-sn, and hyper-sn. The bursty-sn model, driven by intense and episodic SN explosions, produces the highest fluctuations in the star formation rate (SFR). Conversely, the smooth-sn model, characterized by gentler SN feedback, results in minimal SFR variability. The hyper-sn model, featuring a more realistic prescription that incorporates hypernova (HN) explosions, exhibits intermediate variability, closely aligning with the smooth-sn trend at lower redshifts. These fluctuations in SFR significantly affect the $\rm{M_{UV} - M_{halo}}$ relation, a proxy for UVLF variability. Among the models, bursty-sn produces the highest UVLF variability, with a maximum value of 2.5. In contrast, the smooth-sn and hyper-sn models show substantially lower variability, with maximum values of 1.3 and 1.5, respectively. However, in all cases, UVLF variability strongly correlates with host halo mass, with lower-mass halos showing greater variability due to more effective SN feedback in their shallower gravitational wells. The bursty-sn model, though, results in higher amplitudes. Variability decreases in lower mass haloes with decreasing redshift for all feedback models. This study underscores the critical role of SN feedback in shaping the UVLF, and highlights the mass and redshift dependence of its variability, suggesting that UVLF variability may alleviate the bright galaxy tension observed by JWST at high redshifts.

astro-ph.GA↗

arXiv2024

Helium Reionization from Empirical Quasar Luminosity Functions before and after JWST

Recently, models of the quasar luminosity function (QLF) rooted on large observational compilations have been produced that, unlike their predecessors, feature a smooth evolution with time. This bypasses the need to assume an ionizing emissivity evolution when simulating helium reionization with observations-based QLF, thus yielding more robust constraints. We combine one such QLF with a cosmological hydrodynamical simulation and 3D multi-frequency radiative transfer. The simulated reionization history is consistently delayed in comparison to most other models in the literature. The predicted intergalactic medium temperature is larger than the observed one at $z \lesssim 3$. Through forward modeling of the He II Lyman-$α$ forest, we show that our model produces an extended helium reionization and successfully matches the bulk of the observed effective optical depth distribution, although it over-ionizes the Universe at $z\lesssim2.8$ as the effect of small-scale Lyman Limit Systems not being resolved. We thoroughly characterize transmission regions and dark gaps in He II Lyman-$α$ forest sightlines. We quantify their sensitivity to the helium reionization, opening a new avenue for further observational studies of this epoch. Finally, we explore the implications for helium reionization of the large number of active galactic nuclei revealed at $z\gtrsim5$ by JWST. We find that such modifications do not affect any observable at $z\leq4$, except in our most extreme model, indicating that the observed abundance of high-$z$ AGNs does not bear consequences for helium reionization.

astro-ph.GA↗

arXiv2022

Properties of atomic hydrogen gas in the Galactic plane from THOR 21-cm absorption spectra: a comparison with the high latitude gas

The neutral hydrogen 21 cm line is an excellent tracer of the atomic interstellar medium in the cold and the warm phases. Combined 21 cm emission and absorption observations are very useful to study the properties of the gas over a wide range of density and temperature. In this work, we have used 21 cm absorption spectra from recent interferometric surveys, along with the corresponding emission spectra from earlier single dish surveys to study the properties of the atomic gas in the Milky Way. In particular, we focus on a comparison of properties between lines of sight through the gas disk in the Galactic plane and high Galactic latitude lines of sight through more diffuse gas. As expected, the analysis shows a lower average temperature for the gas in the Galactic plane compared to that along the high latitude lines of sight. The gas in the plane also has a higher molecular fraction, showing a sharp transition and flattening in the dust - gas correlation. On the other hand, the observed correlation between 21 cm brightness temperature and optical depth indicates some intrinsic difference in spin temperature distribution and a fraction of gas in the Galactic plane having intermediate optical depth (for 0.02 < $τ$ < 0.2) but higher spin temperature, compared to that of the diffuse gas at high latitude with the same optical depth. This may be due to a small fraction of cold gas with slightly higher temperature and lower density present on the Galactic plane.

astro-ph.GA↗

arXiv2021

Stringent constraint on the radio signal from dark matter annihilation in dwarf spheroidal galaxies using the TGSS

Weakly Interacting Massive Particles (WIMPs) are considered to be one of the favoured dark matter candidates. Searching for any detectable signal due to the annihilation and decay of WIMPs over the entire electromagnetic spectrum has become a matter of interest for the last few decades. WIMP annihilation to Standard Model particles gives rise to a possibility of detection of this signal at low radio frequencies via synchrotron radiation. Dwarf Spheroidal Galaxies (dSphs) are expected to contain a huge amount of dark matter which makes them promising targets to search for such large scale diffuse radio emission. In this work, we present a stacking analysis of 23 dSph galaxies observed at low frequency (147.5MHz) as part of the TIFR-GMRT Sky Survey (TGSS). The non-detection of any signal from these stacking exercises put very tight constraints on the dark matter parameters. The best limit comes from the novel method of stacking after scaling the radio images of the individual dSph galaxy fields after scaling them by the respective half-light radius. The constraint on the thermally averaged cross-section is below the thermal relic cross-section value over a range of WIMP mass for reasonable choices of relevant astrophysical parameters. Such analysis using future deeper observation of individual targets as well as stacking can potentially reveal more about the WIMP dark matter properties.

astro-ph.HE↗