IIAP Publications

Caught in the act: Interaction-driven evolution in the nearby compact galaxy group Robert's Quartet (SCG0018-4854)

Sat, 01 Aug 2026 00:00:00 GMT

Caught in the act: Interaction-driven evolution in the nearby compact galaxy group Robert's Quartet (SCG0018-4854) Keshri, Saili; Barway, Sudhanshu; Mousumi Das; Paswan, Abhishek 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. Open Access; Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Unveiling the nature of barium stars: I. Asteroseismic masses and the evolutionary link between Ba dwarfs and giants

Sat, 01 Aug 2026 00:00:00 GMT

Unveiling the nature of barium stars: I. Asteroseismic masses and the evolutionary link between Ba dwarfs and giants Sarmah, Lupamudra; Bharat Kumar, Y; Campbell, S. W; Maben, Sunayana; Reddy, B. E Context. Barium star systems are excellent sites for studying asymptotic giant branch (AGB) nucleosynthesis, binary evolution, and mass transfer processes. However, an accurate estimation of their fundamental stellar parameters is still lacking. Aims. We measure accurate and precise masses of Ba stars using asteroseismology. This enables us to constrain the nature, origin, and evolution of these binary systems. Methods. Using data from the Transiting Exoplanet Survey Satellite, we made the first extensive asteroseismic mass measurements of Ba stars. Our sample comprises 31 Ba giants and 13 Ba dwarfs. For some, we were able to measure ∆P, thereby ascertaining their evolutionary phase. With reliable asteroseismic masses, we then constructed a grid of stellar models across the relevant mass range, where we accreted AGB material using composition from existing yields. Results. We found that the average masses of the Ba dwarfs and Ba giants are significantly different (1.29 ± 0.09 M⊙ versus 1.96 ± 0.16 M⊙, respectively; with typical individual mass uncertainties of ~10%). However, their mass distributions peak at about the same mass (~1.3 M⊙). While our sample of Ba giants spans the low- and intermediate-mass regime, we found no intermediate-mass Ba dwarfs. The abundance trends of s-process elements ([s/Fe], [hs/Fe], and [ls/Fe]) show an overall anti-correlation with stellar mass, particularly in the low-mass regime (<2 M⊙), for giants and dwarfs. The stellar models adopting Monash AGB yields can satisfactorily reproduce the observed light elements, s, and heavy-s abundance trends simultaneously, with an accreted mass of 0.1--0.5 M⊙ for the majority of the Ba stars. However, the models fail to explain the light-s abundances and, consequently, the [hs/ls] ratio. We found that most Ba stars had AGB companions in the mass range 1--4 M⊙. Conclusions. Our results support an evolutionary scenario in which Ba giants evolve from Ba dwarfs, with mass accretion occurring while the progenitor Ba star is still on the main sequence. In this scenario, a substantial number of intermediate-mass Ba dwarfs are expected. We argue that they remain undetected due to observational bias. We found that post-accretion additional mixing in our models is critical to explain the observed s-process abundances in Ba dwarfs and the low C isotopic ratio (<30) in Ba giants. The mismatch between the model and the observed [hs/ls] ratio suggests that the chemical enrichment of Ba stars cannot be explained by standard single-star AGB yields alone. This may be due to (i) their binary nature altering AGB evolution, (ii) missing or modified nucleosynthesis processes in AGB models, or (iii) additional sources of pollution. Open Access; Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Feeding and feedback in dwarf galaxies (FeeD) I. Evidence of nuclear ultra-fast and galaxy-scale outflows in the dwarf galaxy Arp 151

Sat, 01 Aug 2026 00:00:00 GMT

Feeding and feedback in dwarf galaxies (FeeD) I. Evidence of nuclear ultra-fast and galaxy-scale outflows in the dwarf galaxy Arp 151 Mondal, Santanu; Patel, Ankit; Mezcua, M; Joshi, Ravi; Xu, Y; Aditya, K; Subramanian, S; Rodriguez Morales, V Feeding and feedback regulated by supermassive black holes play a central role in galaxy growth and evolution, yet these processes remain poorly understood in low-mass galaxies. In particular, the presence, properties, and role of nuclear ultra-fast outflows (UFOs) in low-mass galaxy systems are largely unexplored. We analyzed available NuSTAR X-ray observations of Arp 151 and find possible evidence (∼2σ confidence) of a fast outflow with a velocity of ∼0.18c from the central black hole. Furthermore, we have detected an optical galaxy-scale outflow in MaNGA integral field unit data. The estimated nuclear and galaxy-scale mass outflow rates are ∼0.015 M⊙/yr from NuSTAR and ∼0.43 M⊙/yr from MaNGA, respectively. Our estimates suggest that such outflows may significantly regulate the feedback process in the galaxy. A comparison of the kinetics of the UFO and the galaxy-scale outflow indicates that they are in the momentum-conserving phase. This tentative discovery implies that dwarf galaxies are also able to generate UFOs, which so far have been detected in massive galaxies. Thus, the active galactic nucleus feedback may also be important for the evolution of the dwarf galaxies. Open Access; Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Formation and eruption of filament channel in solar active region 12975: insights from observations and simulations of magnetic field evolution

Thu, 20 Aug 2026 00:00:00 GMT

Formation and eruption of filament channel in solar active region 12975: insights from observations and simulations of magnetic field evolution Mishra, Dinesh; Vemareddy, P; Kumar, Brajesh We studied the magnetic field evolution of active region (AR) 12975 using a time-dependent magnetofrictional model. This AR produced two consecutive coronal mass ejections associated with M-class flares on 2022 March 28. The AR exhibited a simple bipolar configuration, with new bipolar flux emerging from March 27. These emerging flux regions evolved through shear motions, forming a filament-channel that ultimately erupted on March 28 at 12:00 UT. The simulation, initialized at 12:00 UT on March 26, is driven by electric fields derived from a time-series of photospheric vector-magnetograms. It reproduces the observed coronal evolution, including the gradual development of a sigmoidal, twisted flux rope (FR) over approximately 50 hr. The modeled temporal evolution of magnetic energy and helicity within the computational domain is consistent with the observed injection of both quantities. Furthermore, the ratio of current-carrying to total relative helicity reaches 0.23 at the time of observed eruption; however, the torus-unstable regime is attained when the helicity ratio reaches 0.32, approximately 7 hr after the observed eruption. Notably, the FR forms adjacent to preexisting magnetic fields, and a substantial portion of the coronal structure does not belong to the FR system. Consequently, the derived helicity thresholds vary and deviate from the proposed value of 0.29. While reproducing filament formation with high morphological accuracy, this study underscores the challenges involved in modeling and evaluating the eruptive behavior of different ARs. Open Access; Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.