Abstract
Dynamical evolution of galaxies is a complex process, especially the centers. Gravitationally coupled gas and stellar discs have been observed to coexist in the galactic discs, including at the center of galaxies. The present work, provide a simple analytic model of nearly Keplerian modes, for co-rotating gravitationally coupled gaseous and stellar discs. We restrict our analysis to ‘slow modes’; their eigenfrequencies being much smaller than the Keplerian orbital frequency to the disc. The dispersion relation using the Wentzel-Kramers-Brillouin (WKB) approximation is formulated and the stability of modes is explored. The presence of gas is found to enhance the instability and slow modes exists only for azimuthal wavenumber, \(m=1\) for the continuum disc. We also analyze the nature of discrete eigen-spectra by quantizing the modes using the Bohr-Sommerfeld quantization condition. The Presence of gas supports the formation of modes with higher temporal frequency and larger wavelength, making them large scale and long-lived. We find that discrete spectra is absent if the ratio of gas mass to stellar mass in galactic disc is greater than 0.1. Though simplified our analysis gives a physically relevant framework for the formation and existence of eccentric disc at the center of galaxies without invoking any external factor. It hence paves a way to explaining the observed asymmetries at the centers of galaxies without provoking the need of continuous source of generation of perturbation.
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Acknowledgements
The authors acknowledge Thapar Institute of Engineering and Technology, Patiala for SEED grant SEED/Money/TU/DORSP/57/3978 to support this research work. Further we acknowledge DST-FIST (Govt. of India) for the grant SR/FST/MS-1/2017/13 to support during the period of the present work. Authors would like to acknowledge H.K. Jassal for providing valuable suggestions during the preparation of the manuscript.
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Prajapati, M., Gulati, M. Enhanced \(m = 1\) WKB instabilities in nearly Keplerian stellar discs due to the presence of gas. Astrophys Space Sci 367, 56 (2022). https://doi.org/10.1007/s10509-022-04077-y
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DOI: https://doi.org/10.1007/s10509-022-04077-y