Title: The observational foundations of density-wave models for spiral structure
Abstract: The validity of some density-wave models of spiral structure is discussed from two points of view: a) the adequacy with which the background structure adopted in these models represents observations of galaxies; b) the consistency of the predicted and observed properties of spiral structure. In the Galaxy, the spiral density waves are governed by the flat subsystem only; although the disk and the halo comprise the bulk of the mass, their contribution to the density waves is insignificant. The model of galactic spiral structure described by Marochnik et al. is further supported by the angular rotational velocity ..cap omega../sub p/=20--25 km sec/sup -1/ kpc/sup -1/ of the spiral pattern derived observationally, as well as by the large-scale distribution observed for H II zones and neutral hydrogen. In particular, the properties and position of the outer Lindblad resonance predicted by the Marochnik theory are confirmed by the presence of ring-shaped gas condensations at the periphery of our own and other galaxies; thus the theory affords a natural explanation of this interesting feature displayed by many spiral galaxies. According to the Marochnik theory, the Galaxy has a corotation region at a radius R/sub c/=10--12 kpc. A galactic shock wave should not developmore » in the vicinity of R/sub c/; hence fewer H II zones should occur there. The rapid drop in the abundance of H II zones from R=5 kpc toward R=10 kpc in the Galaxy (even though the H I density per unit disk surface area remains constant or possibly grows) reinforces this conclusion. A similar agreement between the corotation and outer-resonance positions predicted by the Marochnik theory and the behavior of the H II and H I distribution is observed in a number of other galaxies. The interpretation the Marochnik theory offers for the properties of spiral structure and for its excitation mechanism fully agrees with the results of numerical simulations of stellar disks.« less
Publication Year: 1978
Publication Date: 1978-09-01
Language: en
Type: article
Access and Citation
AI Researcher Chatbot
Get quick answers to your questions about the article from our AI researcher chatbot