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Date and Time of the Query: 2019-06-19 T12:08:25 PDT
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For refcode 2016MNRAS.459.4057G:
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Copyright by Royal Astronomical Society. 2016MNRAS.459.4057G Dynamical effect of gas on spiral pattern speed in galaxies Ghosh, Soumavo; Jog, Chanda J. Abstract. In the density wave theory of spiral structure, the grand-design two-armed spiral pattern is taken to rotate rigidly in a galactic disc with a constant, definite pattern speed. The observational measurement of the pattern speed of the spiral arms, though difficult, has been achieved in a few galaxies such as NGC 6946, NGC 2997, and M 51 which we consider here. We examine whether the theoretical dispersion relation permits a real solution for wavenumber corresponding to a stable wave, for the observed rotation curve and the pattern speed values. We find that the disc when modelled as a stars-alone case, as is usually done in literature, does not generally give a stable density wave solution for the observed pattern speed. Instead the inclusion of the low velocity dispersion component, namely, gas, is essential to obtain a stable density wave. Further, we obtain a theoretical range of allowed pattern speeds that correspond to a stable density wave at a certain radius, and check that for the three galaxies considered, the observed pattern speeds fall in the respective prescribed range. The inclusion of even a small amount (~15 per cent) of gas by mass fraction in the galactic disc is shown to have a significant dynamical effect on the dispersion relation and hence on the pattern speed that is likely to be seen in a real, gas-rich spiral galaxy. Key words: galaxies: individual: M 51, galaxies: individual: NGC 6946, galaxies: ISM, galaxies: kinematics and dynamics, galaxies: spiral, galaxies: structure
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