arXiv subjects

Tapan K. Sasmal

Publications and source records attributed to Tapan K. Sasmal.

6 recordsLinked to original sources

arXiv2026

Identification and Study of Irregular Radio Sources with SKA Continuum Surveys

Radio galaxies show a wide range of morphologies, from regular double-lobed systems to more complex and distorted radio structures. In this chapter, we focus on irregular radio morphologies, defined as sources in which the radio jets and lobes deviate from a straight and symmetric structure. Bent-tail radio galaxies and winged radio galaxies are two important examples of such sources. Bent-tail radio galaxies show curved jets or lobes, mainly shaped by the interaction between radio plasma and the dense intracluster or intragroup medium. Winged radio galaxies show faint off-axis emission, which may be related to plasma backflow, jet reorientation, episodic activity, galaxy mergers, or environmental asymmetry. The Square Kilometre Array (SKA) continuum surveys will provide the sensitivity, angular resolution, frequency coverage, and image quality required to identify and study large samples of such irregular radio galaxies. These data will make it possible to detect faint extended structures, including diffuse tails, weak bridges, remnant lobes, and low-surface-brightness wings. The identification and classification of these sources will require a combination of machine-learning methods, quantitative morphology measurements, multi-wavelength host-galaxy association, and expert visual inspection. The study of irregular radio galaxies with SKA data will help to connect radio morphology with host-galaxy properties, Active Galactic Nucleus (AGN) activity, jet power, and surrounding environment. Such studies will provide important insight into jet-environment interactions, AGN feedback, the dynamical state of galaxy groups and clusters, and the evolution of radio galaxies across cosmic time.

astro-ph.GA↗

arXiv2026

A Morphological Identification and Study of Radio Galaxies from LoTSS DR2. III. The Multiwavelength Analysis of Winged Radio Galaxies

We present a multiwavelength follow-up study of 621 winged radio galaxies (WRGs) recently identified from LoTSS DR2, constituting the largest statistically significant samples of X-shaped (XRGs) and Z-shaped (ZRGs) radio galaxies to date. Our results show that WRGs are predominantly strongly radio-dominated, with XRGs on average more radio-luminous than ZRGs. Their optical hosts are massive elliptical galaxies residing in moderate-density environments. For 270 of XRGs, we measure angular offsets between the radio wings and the optical major axis. While most XRGs show large misalignments consistent with hydrodynamic backflow along the host minor axis, a substantial fraction ($\sim$25\%) exhibits small offsets (<30°), indicating that additional processes, such as jet reorientation, may also play a role. ZRGs, in contrast, are characterized by strongly antisymmetric deformations of their radio lobes pointing toward a coherent mechanism affecting both jets, modulated by local environmental interactions at the lobe termini. Mid-infrared diagnostics indicate merger-related cold gas in many WRGs, particularly XRGs, which also more frequently host powerful AGN, while ZRGs are more often classified as low-excitation radio galaxies (LERGs). This is consistent with our previous results showing that, although most WRGs exhibit FR II morphologies, FR I sources are almost exclusively ZRGs, suggesting that Z-shaped structures are statistically associated with lower jet power and are therefore more susceptible to perturbations. Nevertheless, the physical processes responsible for shaping XRGs and ZRGs need not be fundamentally different. Instead, the final morphology likely reflects the interplay between jet power, jet stability, and the surrounding environment.

astro-ph.GA↗

arXiv2026

A Morphological Identification and Study of Radio Galaxies from LoTSS DR2. I. The "Winged'' Radio Galaxies

We conducted an extensive identification and analysis of various morphological classes and subclasses of radio galaxies using the latest high-resolution data from the second data release of the LOFAR Two-Metre Sky Survey (LoTSS DR2). This paper presents the first results of our large-scale investigation: a new catalog of ``winged" radio galaxies (WRGs). These objects represent a fascinating class of irregular radio galaxies, characterized by a pair of secondary radio lobes (``wings") in addition to the primary active lobes. We identified and cataloged 621 new WRGs and 403 additional candidates. Among the confirmed winged sources, 382 are classified as ``X"-shaped radio galaxies (XRGs), while the remaining 239 are ``Z"-shaped radio galaxies (ZRGs). We also estimated several basic parameters for these winged sources and performed a Fanaroff-Riley (FR) classification. Our results show that the majority of the sources ($\sim$88\%) exhibit edge-brightened radio lobes and high average radio power ($\rm log_{10}[P_{144MHz} / W Hz^{-1}]$ = 26.25), consistent with an FR-II classification. The average spectral index between 144 MHz and 1.4 GHz is --0.84, which is steeper than that found for previously identified winged sources based on higher-frequency data from the VLA Faint Images of the Radio Sky at Twenty-Centimeters (FIRST) survey. This indicates that our study is capable of detecting fainter sources. The median linear size of the winged sources, 498 kpc, confirms that these are large-scale structures, with approximately 16\% having sizes exceeding 0.7 Mpc, making them potential candidates for giant radio galaxies.

astro-ph.GA↗

arXiv2026

A Catalog of 971 FR-I Radio Galaxies from the FIRST Survey via Hybrid Deep Learning and Ridgeline Flux Density Distribution Analysis

We present a catalog of 971 FR-I radio galaxies (FR-Is) identified from the Very Large Array Faint Images of the Radio Sky at Twenty-Centimeters (FIRST) survey. The identifications were made using a hybrid method that combines deep learning with ridgeline flux density distribution analysis. Among these sources, 845 are new discoveries. The catalog comprises sources characterized by edge-darkened double jets, an absence of significant bent morphology, and angular sizes ranging from 23 to 159 arcseconds. Optical and/or infrared counterparts have been identified for 813 FR-Is. Among these, the host galaxies are predominantly (88.1\%) red galaxies, with the remainder (11.9\%) being blue galaxies; notably, most blue galaxies exhibit high radio power. The FR-I sample spans a radio power range of $1.20 \times 10^{21} \leq P_{\rm 1400} \leq 3.55 \times 10^{27} \, {\rm W\,Hz}^{-1}$ at 1400 MHz and reaches redshifts up to $z = 2.307$. The host galaxies have $r$-band absolute magnitudes in the range $-24 \lesssim M_r \lesssim -20$ mag. For the 512 FR-Is with estimates, the black hole masses fall within $10^7 \lesssim M_{\rm BH} \lesssim 7.94 \times 10^9 \, M_{\odot}$. Based on optical emission-line ratios and mid-infrared colors, spectroscopic classification shows that 571 hosts are low-excitation radio galaxies (LERGs) and 59 are high-excitation radio galaxies (HERGs).

astro-ph.GA↗

arXiv2025

A New Catalog of Head Tail Radio Galaxies from the VLA FIRST Survey

The head--tail (HT) morphology of radio galaxies is seen for a class of radio sources where the primary lobes are being bent in the intercluster weather due to strong interactions between the radio jets and their respective intracluster medium. A systematic search has been carried out for new HT radio galaxies from the Very Large Array Faint Images of the Radio Sky at Twenty-Centimeters survey database at $1400\,\mathrm{MHz}$. Here, we present a catalog of 717 new HT sources, among which 287 are narrow-angle tail (NAT) sources whose opening angle between the two lobes is less than $90^\circ$, and 430 are wide-angle tail (WAT) whose opening angle between the two lobes is greater than $90^\circ$. NAT radio sources are characterized by tails bent in a narrow ``V''-like shape; the jet bending in the case of WAT radio galaxies are such that the WATs exhibit wide ``C''-like morphologies. Optical counterparts are found for 359 HT sources. We report HT sources with luminosity ranges $10^{38} \lesssim L_{1.4\,\mathrm{GHz}} \lesssim 10^{45}\,\mathrm{erg\,s^{-1}}$ and redshifts up to 2.01. The various physical properties of these HT sources are mentioned here. Some statistical studies have been done for this large number of newly discovered HT sources.

astro-ph.GA↗

arXiv2020

FIRST winged radio galaxies with X and Z symmetry

X-shaped radio galaxies are a subclass of radio sources that exhibit a pair of secondary low surface brightness radio lobes oriented at an angle to the primary high surface brightness lobes. Sometimes, the secondary low brightened lobes emerge from the edges of the primary high brightened lobes and form a Z-symmetric morphology. We present a systematical search result for X-shaped radio galaxies (XRGs) and Z-shaped radio galaxies (ZRGs) from the VLA Faint Images of the Radio Sky at Twenty-Centimeters (VLA FIRST) Survey at 1.4 GHz. Our search yields a total of 296 number of radio sources, out of which 161 are XRGs and 135 are ZRGs. We have also made optical identification of these sources from the different available literature. J1124+4325 and J1319+0502 are the farthest known XRG and ZRG, respectively. We have estimated spectral index and radio luminosity of these radio sources and made a comparative study with previously detected XRGs and ZRGs. The average value of luminosities for XRGs is higher than that of ZRGs. With the help of a large sample size of the newly discovered XRGs and ZRGs, various statistical properties of these sources are studied. Out of 161 XRGs presented in the current paper, 70% (113) are FR II radio galaxies and 13% (20) are FR I radio galaxies. For 28 XRGs, the morphology is complex and could not be classified. For XRGs, the statistical studies are done on the angle between the major axis and minor axis and the relative size of the major and minor axes. For the ZRGs a statistical study is done on the angular size.

astro-ph.GA↗