Sudhanshu Barway

This study investigates the role of internal structures, such as stellar bars and active galactic nuclei (AGN), in shaping galaxy evolution using 7408 galaxies (2641 barred) from the Sloan Digital Sky Survey IV Mapping Nearby Galaxies at Apache Point Observatory survey. Our analysis spans a wide stellar mass range, from dwarf to massive galaxies, examining how internal and environmental processes regulate galaxy evolution. Galaxies are categorized by morphology (ellipticals, E; lenticulars, S0s; early-type spirals, ETS; and late-type spirals, LTS), environment, and the presence of a bar. We find that barred galaxies have a higher median specific star formation rate (sSFR) than unbarred galaxies across most stellar mass intervals. This difference varies with host morphology, with LTS and S0 galaxies showing different trends across stellar mass intervals. The environmental trends of barred and unbarred galaxies are broadly similar within the same mass intervals. In AGN hosts, barred Seyferts tend to lie near the star-forming–green valley boundary, while barred LINERs preferentially occupy the green valley. We further examine the relation between stellar bars and black hole mass and find that barred galaxies host systematically lower black hole masses than unbarred galaxies, with environmental effects appearing to play a secondary role in shaping these differences. A multivariate regression analysis also shows that the positive bar–sSFR association remains statistically significant for star-forming galaxies after accounting for stellar mass, local density, AGN, and morphology. Our results highlight the interconnected roles of stellar bars, stellar mass, morphology, and environment in shaping galaxy star formation, providing new insights into the role of stellar bars in galaxy evolution.

We present a spatially resolved multiwavelength study of the compact galaxy group Robert’s Quartet (RQ; SCG0018-4854), aimed at understanding interaction-driven galaxy evolution in dense environments. The system comprises four galaxies (NGC 87, NGC 88, NGC 89, and NGC 92) that span a range of masses and evolutionary states. Using UV-to-IR data from GALEX, DECaLS, MUSE/VLT (IFU), VISTA/VIRCAM, 2MASS, and WISE, we investigated the interplay between kinematics, star formation, and stellar populations across the group. The spatially resolved analysis reveals disturbed stellar and gas kinematics, enhanced turbulence, and asymmetric structures in all members, consistent with repeated gravitational interactions. The most massive galaxy, NGC 92, exhibits prominent tidal features, a bar, and ring-like star-forming structures, indicative of interaction-driven gas inflows. Another massive member, NGC 89, shows suppressed star formation and signatures of active galactic nucleus-driven feedback. Lower-mass galaxies NGC 88 and the dwarf galaxy NGC 87, by contrast, display enhanced star formation and, in one case, kinematic decoupling between stellar and gaseous components consistent with recent gas accretion. Combining UV-based age estimates with non-parametric star formation histories, we constrain the recent interaction timescale of the group to ≲500 Myr, whereas the crossing timescale is 424 Myr. These results indicate that RQ is a dynamically young system undergoing ongoing assembly, where interactions, gas exchange, and feedback processes are actively shaping galaxy evolution. The dynamical complexity of the group further suggests that its present configuration may involve more than four progenitor components. In this context, RQ provides a valuable nearby analogue of compact, rapidly evolving groups observed at high redshift by recent JWST observations, offering a resolved view of the physical processes governing galaxy assembly in the early Universe.

Context. Giant Low Surface Brightness galaxies (gLSBGs), such as Malin 1, host extended stellar and gaseous discs exceeding 100 kpc in radius. Their formation and evolution remain debated, with interactions with satellite galaxies and accretion streams proposed as key contributors. Malin 1 presents multiple nearby and distant satellites. Additionally, it exhibits two giant stellar streams, the largest extending 200 kpc in projection, likely related to past interactions. Aims. We investigate the orbital dynamics of Malin 1’s satellites and their possible connections with the observed stellar streams, testing their nature with different formation scenarios. Methods. We constructed gravitational potentials for Malin 1 using optical and rotation curve data, incorporating stellar, gaseous, and dark matter (DM) components. We explored a wide orbital parameter space to determine whether the candidate progenitors of the stellar streams could have originated from past interactions, testing both Navarro-Frenk-White (NFW) and the pseudo-isothermal (ISO) halo profiles. Results. Among several explored scenarios, some produced bound orbital solutions. The ISO halo model, with mass of M_ ̊m Virial ≈ 2.6 ≈ 1.4 10^ 12 favours bound satellite orbits more than the NFW model, that has a lower mass of M_ ̊m Virial 10^ 12 These orbital models show that the giant stellar streams could be substructures of some satellites galaxies located along their leading and trailing orbital trajectories. Furthermore, our analysis indicates that the most distant Malin 1 satellite (eM1) could have reached its orbital pericentre sim1.6 Gyr ago, while the nearest companions could have interacted as early as sim100 Myr ago. At the same time, one of the closest companions would still be under a strong interaction. Another close companion displays both leading and trailing arms in a radial orbit, although it also shows a polar orbit. Furthermore, we identify some unbound orbital solutions that could link some satellites with streams. Conclusions. The observed alignment of satellites and streams indicates that past interactions likely shaped aspects of Malin 1’s morphology. Our orbital modelling constrains possible progenitors of the observed stellar streams and their orbital histories, providing new insights into the dynamical evolution of gLSBGs. Our findings are consistent with results reported very recently by other studies using Malin 1 kinematic data.

We investigate the interplay between morphology, specific star formation rate (sSFR), and local environment using a sample of 7408 galaxies from the fourth-generation Sloan Digital Sky Survey Mapping Nearby Galaxies at Apache Point Observatory survey. Our analysis spans stellar masses from dwarf to massive galaxies, enabling a unified view of how stellar mass and environment regulate galaxy evolution. Galaxies are classified by morphology (ellipticals (E), lenticulars (S0s), early-type spirals (ETS), and late-type spirals (LTS)) and local environmental density, with star formation activity traced using sSFR. Low-mass galaxies ( log ( M ⋆ / M ⊙ ) < 10 ) are predominantly star-forming and dominated by LTS, whereas high-mass galaxies ( log ( M ⋆ / M ⊙ ) ≥ 10 ) are dominated by ETS and are largely quenched. By separating dwarf ( log ( M ⋆ / M ⊙ ) ≤ 9.5 ) and intermediate-mass galaxies ( 9.5 < log ( M ⋆ / M ⊙ ) < 10 ), we find that dwarf galaxies remain predominantly star-forming with only weak environmental dependence, whereas intermediate-mass galaxies exhibit clearer environmental trends toward quenching. Using the D4000 index as a tracer of long-term stellar population aging, we further show that dwarf E and S0s host systematically younger stellar populations than their intermediate-mass counterparts, implying reduced quenching efficiency and more gradual environmental processing in the dwarf regime. This distinction is not evident among spiral galaxies, whose stellar population properties are comparatively insensitive to the dwarf versus nondwarf classification. Overall, these results indicate that the commonly defined low-mass galaxy population is not homogeneous and that dwarf and intermediate-mass galaxies show systematically different evolutionary trends. Treating them separately is therefore essential for interpreting galaxy evolution in the low-mass regime.

We investigate how the environment of a dynamically unrelaxed galaxy cluster influences the structure and dynamics of stellar bars. In particular, we examine cluster-centric variations in normalised bar size and bar pattern speed in Abell,2199. Our analysis is based on 578 spectroscopically confirmed members of Abell,2199, including a master sample of 325 galaxies with homogeneous stellar mass and star formation rate measurements. We identify 39 barred galaxies and measure their structural properties using isophotal ellipse fitting and three-component (bulge+disc+bar) photometric decompositions. For 22 barred galaxies with MaNGA integral-field spectroscopy, we estimate bar pattern speeds using the Tremaine--Weinberg method, obtaining robust measurements for 12 galaxies. Stellar population age and projected specific angular momentum are analysed using R_ e and λ_ R_ e from the MaNGA Pipe3D catalogue. Abell,2199 exhibits star formation--density and morphology--density relations despite its non-relaxed dynamical state. Early-type spiral (ETS) barred galaxies show systematic cluster-centric variations in normalised bar size, with relatively larger bars towards the cluster centre and smaller bars at intermediate radii. A corresponding variation in bar pattern speed with cluster-centric distance is also observed. These trends motivate a division at vir , within which morphology-dependent environmental signatures become clearer, as barred galaxies in the inner region tend to host older stellar populations and lower projected angular momentum than those in the outskirts, with ETS+Bar galaxies retaining higher angular momentum compared to S0+Bar galaxies at comparable radii.

We present a comprehensive multiwavelength study of a bright gamma-ray burst GRB 230204B, analyzing both prompt and afterglow emissions. This GRB is highly energetic, with an isotropic equivalent energy emission of E _iso ∼ 2.2 × 10 ⁵⁴ erg released during the prompt emission. The GROWTH-India Telescope discovered a bright afterglow ( m _r = 15.55) that fades rapidly (∝ t ^−1.82 ). The prompt emission shows a strong thermal photospheric emission along with a nonthermal high-energy component. We explore the evolution of these components and find them to be consistent with the theoretical expectations of the fireball model. Afterglow modeling reveals an energetic jet ( E _γ ≳ 10 ⁵² erg) expanding into a wind-type medium viewed nearly on-axis, suggesting a massive star progenitor with strong winds. We also explore correlations between the prompt emission and afterglow that may help to place GRB 230204B within the broader context of the long GRB population.

We present the searches conducted with the Zwicky Transient Facility (ZTF) in response to S250206dm, a bona fide event with an online false alarm rate of one in 25 yr, detected by the International Gravitational Wave Network. Although the event is significant, the nature of the compact objects involved remains unclear, with at least one likely neutron star. ZTF covered 68% of the last refined Bilby localization region, though we did not identify any likely optical counterpart. We describe the ZTF strategy, potential candidates, and the observations that helped rule out candidates, including sources circulated by other collaborations. Similar to Ahumada et al., we perform a frequentist analysis, using simsurvey , as well as Bayesian analysis, using nimbus , to quantify the efficiency of our searches. We find that, given the nominal up-to-date distance to this event of 373 ± 104 Mpc, our efficiencies are above 10% for KNe brighter than −17.5 absolute magnitude. Assuming the optical counterpart known as kilonova (KN) lies within the ZTF footprint, our limits constrain the brightest end of the KN parameter space. Through dedicated radiative transfer simulations of KNe from binary neutron star (BNS) and black hole–neutron star mergers, we exclude parts of the BNS KN parameter space. Up to 35% of the models with high wind ejecta mass ( M _wind ≈ 0.13 M _⊙ ) are ruled out when viewed face-on ( cos θ obs = 1.0 ). Finally, we present a joint analysis using the combined coverage from ZTF and the Gravitational Wave Multimessenger Dark Energy Camera Survey. The joint observations cover 73% of the Bilby localization region, and the combined efficiency has a stronger impact on rising and slowly fading models, allowing us to rule out 55% of the high-mass KN models viewed face-on.

AT 2022cmc is the first on-axis jetted tidal disruption event (TDE) to be discovered at optical wavelengths. The optically bright nature of AT 2022cmc presents an unprecedented opportunity to place this jetted TDE in the context of the larger optically selected thermal TDE population and explore potential connections to optical TDE subclasses, particularly the class of luminous TDEs that lack optical spectral features. In this work, we present late-time optical observations of AT 2022cmc, both imaging and spectroscopy, that extend the optical dataset to ∼160 days from the first detection in the observed frame. The light curve clearly evolves from red to blue, which we interpret as a transition from a nonthermally dominated spectral energy distribution (SED) to thermally dominated SED. By accounting for the nonthermal emission evident in the optical SED at early times, we extract the properties of the thermal emission and compare to a sample of optically selected thermal TDEs. We find that the properties of AT 2022cmc are consistent with previous correlations found for the evolution and properties of thermal TDEs, with the thermal properties of AT 2022cmc aligning with the class of featureless and luminous TDEs. The confirmation of this similarity motivates the importance of prompt and multiwavelength follow-up of featureless and luminous TDEs in order to further explore the connection they have with jetted TDEs.