Binil Aryal

A small system of typically 4–10 galaxies that appear to be isolated from other galaxies and situated very close to one another on the sky leading to tidal distortions, gas stripping and star bursts is called a Hickson Compact Group (HCG). We present a spectroscopic analysis of four member galaxies of HCG 7: NGC 192, NGC 196, NGC 197, and NGC 201, using data from the Sloan Digital Sky Survey (SDSS) Data Releases 12. Emission lines in the galaxy spectra are modeled with Gaussian profiles, and the Hα line is used to estimate Star Formation Rates (SFRs) and gas-phase metallicities. After extinction correction, we derive SFRs of 0.284 M☉/year, 0.222 M☉/year, and 0.034 M☉/year for the star-forming galaxies, NGC 192, NGC 201, and NGC 197, respectively with corresponding gas-phase metallicities (12 + log(O/H)) of 8.64 dex, 8.55 dex, and 8.56 dex. In contrast, NGC 196 shows no detectable Hα emission, consistent with a quiescent spectrum. The absence of a significant star-forming interstellar medium in NGC 196 may be attributable to environmental processes, with tidal stripping being the most probable quenching mechanism in the dense HCG 7 environment.

Scaling relations are fundamental tools for exploring the morphological properties of galaxies and understanding their formation and evolution. Typically, galaxies follow a scaling relation between mass and size, measured by effective radius. However, a compact class of galaxies exists as outliers from this relation, and the origin of these compact galaxies in the local universe remains unclear. In this study, we investigate the compact dwarf galaxy SDSS J134313.15+364457.5 (J1343+3644), which is the result of a merger. Our analysis reveals that J1343+3644 has a half-light radius of 482~pc, significantly smaller than typical galaxies with the same brightness ($M_\text{r} = -19.17$ mag). With a high star-formation rate (SFR) of 0.87~M$_{\sun}$ year$^{-1}$, J1343+3644 is expected to evolve into a compact elliptical galaxy in a few million years. J1343+3644 could, therefore, be a progenitor of a compact elliptical galaxy. The phenomenon happened in early universe, where compact galaxies were common.

A low flux density region nearby white dwarf WD1334-678 in the 140 µm AKARI survey maps has been systematically searched and found a far-infrared cavity centered at R.A. (J2000) = 13^h38^m14.4^s, Dec.(J2000) = −68^◦40’42”, in which minimum flux is 19.5 MJy/sr at 90 µm wavelength. The physical properties (Size, dust color temperature, dust mass) and thermodynamic property (Planck function distribution) of the cavity using 140 µm and 90 µm AKARI survey data. The size of the cavity is found to be 0.17^◦× 0.12^◦ has been presented. The dust color temperature is found in the range 17.70 ± 0.01 K to 18.81 ± 0.01 K. The Plank function distribution along major and minor diameters shows a very good agreement with sinusoidal fitting. The period of oscillation of dust particles along major and minor diameters are 3.2 Wm^-2Sr^-1Hz^-1arcmin^-1and 1.6 Wm^-2Sr^-1Hz^-1arcmin^-1, respectively. BIBECHANA 18 (2) (2021) 130-137

We studied dust environment such as flux, temperature, mass and inclination angle of the cavity structure around the C-rich Asymptotic giant branch star in 60 μm and 100 μm wavelengths band using Infrared Astronomical Survey. We observed the data of AGB star having IRAS name 01142+6306 corresponding to R.A.(J2000)= 01h 17m 33.504s and Dec.(J2000)= 630 22’ 4.98’. Flexible image transport system image was downloaded from Sky View Observatory; we obtained the surrounding flux density using software Aladinv2.5. The dust color average temperature and mass are found to be 25.08 K and 4.731026 kg (0.00024 Mʘ) respectively. The dust color temperature ranges from 18.76 ± 3.16 K to 33.21 ± 4.07 K. The isolated cavity like structure around AGB star has extension 45.67 parsec and contraction 17.02 parsec was observed using detailed calculation. The core region is found to be edge-on having inclination angle 79.46o. BIBECHANA 16 (2019) 31-40

We study the active region in the interstellar medium in which the process of cavity formation is expected. The interaction between wind and its surroundings in the interstellar medium (ISM) provides a laboratory to study the behavior of dust particles. The information obtained from the dust colour temperature and dust mass of WD2116+675 will be presented. It is found that the dust colour temperature and dust mass lie in the range 20 K to 22.3 K and 2.1×1023 kg to 2.9×1023 kg respectively. With the help of number density, flux density, dust colour temperature and dust mass maps, the variation of temperature and mass in different position of dust will be presented and discussed. BIBECHANA 15 (2018) 43-49

We worked on POSSII and ESO films and measured the diameters and position angles of 5 688 galaxies in 34 clusters using 25-fold magnification microscope. The position angle distributions of galaxies in the clusters are studied. For this, chi-square, auto-correlation and the Fourier tests are carried out. The preferred position angle distribution of galaxies in the cluster is found to be independent of the mean radial velocity of the cluster. Possible explanations of the result will be discussed. The Himalayan Physics Vol. 4, No. 4, 2013 Page: 1-9 Uploaded date: 12/22/2013

We study the spatial orientations of angular momentum vectors of galaxies in six rotating clusters (A954, A1139, A1399, A2162, A2169 and A2366) that show a single number-density peak around the cluster centre with a spatial segregation of high- and low-velocity galaxies. The positions, position angles and inclination angles are used to covert two-dimensional observed parameters into three-dimensional angular momentum vectors of the galaxy. The expected isotropic distribution curves are determined by running numerical simulations. The chi-square, autocorrelation, Fourier, Kolmogorov–Smirnov and Kuiper V tests are carried out in order to examine non-random effects in the expected isotropic distributions. In general a random orientation of angular momentum vectors of galaxies is found in all six rotating clusters supporting hierarchy model of galaxy formation. It is found that the vanishing angular momenta is preferred by the rotating clusters which are in dynamical equilibrium and have larger value of velocity dispersion. Possible explanations of the results will be discussed.