arXiv subjects

Kshitij Chavan

Publications and source records attributed to Kshitij Chavan.

4 recordsLinked to original sources

arXiv2025

SAGAN-VI: When Jets Meet Filaments -- Environmental Imprints on the Growth of Giant Radio Galaxies

Giant radio galaxies (GRGs) represent the largest individual astrophysical structures, rivalling galaxy clusters in physical extent. Understanding how they attain such scales demands examining their large scale cosmic surroundings, particularly the under explored filament environment. We quantify the three dimensional (3D) distance of GRGs from the nearest filament spine; test how this distance correlates with their growth and formation of different morphological classes; assess whether their radio jets exhibit preferred orientations relative to filament axes; and examine how filament anisotropy from spine to periphery modulates radio morphology. We employed a filament catalogue from the SDSS together with the largest GRG catalogue currently available. For each source, we measured the comoving distance to the nearest filament spine, the projected jet spine orientation angle, and quantified lobe asymmetry via the arm length ratio (ALR). These metrics trace proximity, directionality, and the impact of filamentary environment on morphology. We then compared GRGs with a control sample of small radio galaxies (SRGs) to constrain the environmental factors that regulate the attainment of giant sizes. We validated the robustness of our results via bootstrap resampling and non parametric statistical tests. Our results show that GRGs and SRGs have similar filament occupancy. By contrast, GRGs preferentially display larger alignment angles relative to filament spines, while SRG orientations are consistent with a random distribution. GRGs further show enhanced morphological asymmetry, reflected in lower ALR values than SRGs. Attainment of giant sizes is not governed by proximity to filaments; rather, it correlates with jet filament alignment. Abridged.

astro-ph.GA↗

arXiv2024

Search and analysis of giant radio galaxies with associated nuclei (SAGAN) V. Study of giant double-double radio galaxies from LoTSS DR2

To test the hypothesis that megaparsec-scale giant radio galaxies (GRGs) experience multiple epochs of recurrent activity leading to their giant sizes and to understand the nature of double-double radio galaxies (DDRGs), we have built the largest sample of giant DDRGs from the LOFAR Two Metre Sky Survey (LoTSS) data release 2. This sample comprises 111 sources, including 76 newly identified DDRGs, with redshifts ranging from 0.06 to 1.6 and projected sizes between 0.7 Mpc and 3.3 Mpc. We conducted a detailed analysis to characterise their properties, including arm-length ratios, flux density ratios of pairs of lobes, and misalignment angles. These measurements allow us to study the symmetry parameters, which are influenced by the immediate and large-scale environments of DDRGs. Our study shows that based on the observed asymmetries of the inner lobes, the cocoons in which the inner lobes of DDRGs grow are often (~26%) asymmetrically contaminated with surrounding material from the external medium. Our analysis also reveals highly misaligned DDRGs, which could be due to environmental factors and/or changes in the supermassive black hole jet ejection axes. By studying the misalignment angles, we assess the stability of the jets in these systems in relation to their environment. For the first time, we systematically characterised the large-scale environments of DDRGs, identifying their association with dense galaxy clusters and revealing the influence of cluster weather on their morphologies. We discovered a DDRG in a distant galaxy cluster at z ~ 1.4, confirming that dynamic cluster environments can induce significant misalignment in DDRGs, consistent with simulations. Additionally, we identified two gigahertz peaked-spectrum (GPS) candidates in DDRG cores and a potential triple-double candidate, which, if confirmed, would be the fifth known case. Abridged.

astro-ph.GA↗

arXiv2024

Status of Astronomy Education in India: A Baseline Survey

We present the results of a nation-wide baseline survey, conducted by us, for the status of Astronomy education among secondary school students in India. The survey was administered in 10 different languages to over 2000 students from diverse backgrounds, and it explored multiple facets of their perspectives on astronomy. The topics included students' views on the incorporation of astronomy in curricula, their grasp of fundamental astronomical concepts, access to educational resources, cultural connections to astronomy, and their levels of interest and aspirations in the subject. We find notable deficiencies in students' knowledge of basic astronomical principles, with only a minority demonstrating proficiency in key areas such as celestial sizes, distances, and lunar phases. Furthermore, access to resources such as telescopes and planetariums remain limited across the country. Despite these challenges, a significant majority of students expressed a keen interest in astronomy. We further analyze the data along socioeconomic and gender lines. Particularly striking were the socioeconomic disparities, with students from resource-poor backgrounds often having lower levels of access and proficiency. Some differences were observed between genders, although not very pronounced. The insights gleaned from this study hold valuable implications for the development of a more robust astronomy curriculum and the design of effective teacher training programs in the future.

physics.ed-ph↗

arXiv2023

A giant radio galaxy with three cycles of episodic jet activity from LoTSS DR2

The excellent sensitivity and optimum resolution of LoTSS DR2 at 144 MHz has enabled us to discover a giant radio galaxy (J1225+4011) with three distinct episodes of jet activity, making it a member of a class of objects called triple-double radio galaxies (TDRGs). The source extends overall up to 1.35 Mpc in projected size, with the second episode extending to 572 kpc, and the inner episode to 118 kpc. J1225+4011 is only the fourth radio source showing a triple-double radio structure. All four sources have overall sizes greater than 700 kpc, making them giants. We also present the LoTSS 144 MHz map of the TDRG J0929+4146 and report its updated size. Lastly, we have summarised and discussed the radio properties of all TDRGs for the first time to understand their growth and evolution. Our observations suggest that the power of their jets may decrease with time.

astro-ph.GA↗