1. which characteristics are considered most typical of an old galaxy in decline?
2.which factor is essential to the initial formation of the galaxys for either of the theory's describing galaxy evolution
1. Some characteristics considered typical of an old galaxy in decline include a lack of recent star formation, a red color indicative of older stars dominating the population, and a lack of gas and dust necessary to form new stars.
2. The factor essential to the initial formation of galaxies according to both the hierarchical merging model and the monolithic collapse model is the presence of dark matter. Dark matter provides the gravitational pull necessary to aggregate ordinary matter and form the first structures that eventually evolve into galaxies.