# Effects of Non-Circular Motions on Azimuthal Color Gradients - Astrophysics > Cosmology and Nongalactic Astrophysics

Effects of Non-Circular Motions on Azimuthal Color Gradients - Astrophysics > Cosmology and Nongalactic Astrophysics - Download this document for free, or read online. Document in PDF available to download.

Abstract: Assuming that density waves trigger star formation, and that young starspreserve the velocity components of the molecular gas where they are born, weanalyze the effects that non-circular gas orbits have on color gradients acrossspiral arms. We try two approaches, one involving semi-analytical solutions forspiral shocks, and another with magnetohydrodynamic MHD numerical simulationdata. We find that, if non-circular motions are ignored, the comparison betweenobserved color gradients and stellar population synthesis models would inprinciple yield pattern speed values that are systematically too high forregions inside corotation, with the difference between the real and themeasured pattern speeds increasing with decreasing radius. On the other hand,image processing and pixel averaging result in systematically lower measuredspiral pattern speed values, regardless of the kinematics of stellar orbits.The net effect is that roughly the correct pattern speeds are recovered,although the trend of higher measured $\Omega p$ at lower radii as expectedwhen non-circular motions exist but are neglected should still be observed. Weexamine the Martinez-Garcia et al. 2009 photometric data and confirm thatthis is indeed the case. The comparison of the size of the systematic patternspeed offset in the data with the predictions of the semi-analytical and MHDmodels corroborates that spirals are more likely to end at Outer LindbladResonance, as these authors had already found.

Author: ** Eric E. Martinez-Garcia, Rosa A. Gonzalez-Lopezlira, Gilberto C. Gomez**

Source: https://arxiv.org/