AR-2019-2020
Figure 9: . Narrowband H α imaging of nearby Wolf-Rayet galaxies The aim of this work is to explore the formation and evolution of Wolf-Rayet (WR) galaxies. The WR galaxies are subset of HII galaxies. They are classified based on broad optical emission features of HeII λ 4686 and CIV λ 5808 lines, originated in the stellar winds from a substantial population of WR stars. Thease features in WR galaxies are often seen after 2 − 5 Myr of intitial star formation for a short duration ( < 0.5 Myr), until WR population end their lives in supernovae. Therefore, these galaxies are ideal systems to explore onset of star formation and its triggering mechanism. Abhishek Paswan, Kanak Saha and Amitesh Omar studied using their own narrowband H α imaging observations along with other archival data from GALEX, SDSS, IRAS, FIRST and NVSS surveys. Most of the galaxies show a morphological feature related to galaxy tidal interactions and mergers process (e.g., see Fig. 10). Here it is found that these WR galaxies have exprienced tidal interactions and/or mergers with low-luminous dwarf galaxy or HI cloud that most likely triggered the recent star formation in galaxies. These galaxies are further put in the main sequence (MS) relation (a relation between stellar-mass and star formation rate). They followed a similar MS relation as known for non-WR star-forming galaxies, suggesting that WR systems evolve in a similar fashion as normal star-forming galaxies evolve. In case of WR galaxies, it is, however, noticed that the scatter in the relation is comparitively higher than that of normal star-forming galaxies. It is mainly due to merging/interacting nature of the WR systems. Incoherent fast variability of X-ray obscurers: The case of NGC 3783 Variation in absorption of X-ray radiation emitted from the Active Galactic Nuclei (AGN) is a phe- nomenon seen in the X-ray spectra of several active galaxies. Studying this phenomenon utilizing the high X-ray spectra from X-ray instruments and the computer simulations allow us to estimate the several physical properties of the variable ionized gas present in the vicinity of the super-massive
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