Stellar Orbital Studies in Normal Spiral Galaxies. Ii. Restrictions on Structural and Dynamical Parameters on Spiral Arms

Abstract

Making use of a set of detailed potential models for normal spiral galaxies, we analyze disk stellar-orbital dynamics as the structural and dynamical parameters of spiral arms (mass, pattern speed, and pitch angle) are gradually modified. With this comprehensive study of ordered and chaotic behavior, we constructed an assemblage of orbitally supported galactic models and plausible parameters for orbitally self-consistent spiral arm models. We find that to maintain orbital support for the spiral arms, the spiral arm mass, M sp , must decrease with the increase of the pitch angle, i. If i is smaller than 10 , M sp can be as large as 7% , 6% , or 5% of the disk mass, for Sa, Sb, and Sc galaxies, respectively. If i increases up to 25 , the maximum M sp is 1% of the disk mass, independent of morphological type, in this case. For values larger than these limits, spiral arms would likely act as transient features. Regarding the limits posed by extreme chaotic behavior, we find a strong restriction on the maximum plausible values of spiral arm parameters on disk galaxies beyond which chaotic behavior becomes pervasive. We find that for i smaller than 20 , 25 , or 30 , for Sa, Sb, and Sc galaxies, respectively, M sp can go up to 10% , of the mass of the disk. If the corresponding i is around 40 , 45 , 50 , M sp is 1% , 2% , 3% of the mass of the disk. Beyond these values, chaos dominates phase space, destroying the main periodic orbits and the neighboring quasiperiodic orbits.

The imprint of arms and bars on rotation curves: in-plane and off-plane

“…This, of course, depends on the mass of the spiral arms; models with different mass ratios might find a different correlation, but we consider that our choice for the masses is well founded on galactic orbital studies (e.g. Pérez-Villegas et al 2015b).…”

Dynamics of Thick, Open Spirals in PERLAS Potentials∗

“…Having in mind to model the open spirals of an Sc type galaxy, we adopted the parameters used for that purpose by Pérez-Villegas et al (2015). We briefly summarize them in Table 1.…”