Asymmetries and anisotropies in the cold gas random motions in nearby galaxies [Feb. 25, 2021]


PhD Defense of Paul Adamczyk (Laboratoire d'Astrophysique de Marseille)

I carried out the very first systematic study of the random movements of cold gas on a carefully selected sample of 15 spiral galaxies extracted from the sample HI THINGS and 15 other spiral galaxies from the sample HI WHISP. This study is motivated by the systematic search for anisotropies in the velocity dispersions fields, as was discovered in the galaxy Messier 33 (M33). This anisotropy would indicate that the neutral and cold gas of the interstellar medium would be distributed in dense clusters and that it would therefore be less subject to collisions than expected, which would limit the dissipation of its energy. I show in this thesis that the result discovered in M33 is not confirmed for other galaxies of the same nature and that this particularity of M33 is probably linked to a projection effect. However, by analyzing these velocity dispersion fields using Fourier transforms, I discovered the presence of a 4th order signal, exhibiting a systematic alignment of pi/4 with respect to the major axis . Through two different methods, I confirm the physical reality of this signal, and I suggest different ways to interpret it. Among these, a discussion of instrumental effects is detailed, as well as a possible explanation by anisotropy effects of a different nature.

Tags: astrophysics galaxies kinematics neutral gas velocity dispersion




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