Examining Star Formation in the Evolution of Elliptical Galaxies by Max Watzky (V), Milenka Men (V), Inimai Subramanian1, Juliana Karp1 1
Astronomy Camp, University of Arizona, Tucson, AZ
Abstract The predominant theory of galaxy evolution holds that elliptical galaxies are formed when two or more spiral galaxies merge with one another. We hypothesized that if elliptical galaxies do indeed form in this way, they would exhibit a low star formation rate (SFR) compared to other types of galaxies, as they had exhausted their reserves of star-forming gas in violent collisions. In order to test this hypothesis, we used a hydrogen-alpha (H-alpha) filter, which isolates light from the ionized hydrogen found in stellar nurseries, to image star-forming regions in multiple galaxies at different stages in the galaxy merger process. Although we are still in the process of drawing quantitative measurements from the data, we speculate that star formation in the sample elliptical galaxy is less pronounced than in the sample spiral and merging galaxies, indicating that it may have been formed in a galaxy merger. Introduction According to Hubble’s Galaxy Classification System, there are four major types of galaxies: spiral, barred spiral, elliptical, and irregular. Spiral and barred spiral galaxies like the Milky Way were formed by collapsed clouds of gas that clumped together into larger hierarchical structures. Many spiral galaxies exist in structures known as galaxy clusters, which consist of several galaxies gravitationally bound to one another. Within such clusters, spiral galaxies frequently collide and merge with one another. As galaxy mergers take place, high-density regions of interstellar gas collide, creating an environment of enhanced star formation. In these violent events, the merging galaxies burn through their reserves of star-forming gas, meaning that the resulting galaxies would then exhibit relatively little active star formation. Elliptical galaxies, which have well-established
Figure 1: M106 in all visible light
Figure 2: M106 in H-alpha
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