The power spectrum of the residual rotation curve velocity as a probe of past mergers

Abstract

According to the $\Lambda CDM$ cosmological framework, galaxies underwent multiple mergers in their history. In this paper we propose to use the power spectrum of the residual fluctuations of the rotation curve velocity as a probe of past mergers. The proposition relies on the assertion that mergers are expected to induce large scale flows and in case of major mergers shocks are induced as well. Instabilities of the large scale flows and shocks could generate a large scale turbulence whose size is comparable to the galactic disk dimensions. We develop expressions relating underlying turbulence spectral function to the observational power spectrum of the residual of the rotation curve velocity. This relation can be used to test whether turbulence exists in a given galaxy. The method is applied to the regular spiral galaxy NGC3198 with the conclusion that it underwent a minor merger about 7 Gyr ago.