Eric E. Martinez-Garcia, Rosa A. Gonzalez-lopezlira
Azimuthal age/color gradients across spiral arms are a signature of long-lived spirals. From a sample of nineteen normal (or weakly barred) spirals where we have previously found azimuthal age/color gradient candidates, thirteen objects were further selected if a 2-armed grand-design pattern survived in a surface density stellar mass map. Mass maps were obtained from optical and near-infrared imaging, by comparing with a Monte Carlo library of stellar population synthesis models that allowed us to obtain the mass-to-light ratio in the J-band, (M/L)_J, as a function of (g-i) vs. (i-J) color. The selected spirals were analyzed with Fourier methods in search for other signatures of long-lived modes related to the gradients, such as the gradient divergence towards corotation, and the behavior of the phase angle of the two-armed spiral in different wavebands, as expected from theory. The results show additional signatures of long-lived spirals in at least 50% of the objects.
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http://arxiv.org/abs/1301.6634
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