Red and Blue: A study of Galaxies

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by Samuel Trusty

Presentations should be well organized, and luckily they normally are. The presentation I did about galaxies about an hour ago was one of those kinds. We were presenting about the colour of a galaxy affecting the local density, which is how close the galaxies are together. Our research for our project went well despite some problems, although we eventually reached a surprising conclusion that we couldn’t have predicted from the start.

The research question we had evolved over time but we concluded, “Does the colour of a galaxy effect its local density” our hypothesis was that younger blue galaxies would be closer together and older red galaxies would be farther apart because we thought that, like young stars, galaxies would form in clusters. Even when we got the answer to our first question it gave us more questions to look into.

Our research hit a few blocks. At first we just sorted the galaxies between colours and made local density histograms for them. We had our first problem when we couldn’t figure out what a large local density is since the range went into the negatives. We had a lot of summary stats that showed things like means and medians so we used the median as a threshold between small and large. We eventually figured out that we should be looking at standard deviation which shows how far from the average the data can be. It showed us that red galaxies had a high Standard deviation compared to blue. This was eventually distilled down to massive red elliptical galaxies which had a large local density.

This data disproved our first question but we wanted to know why, we figured out using R90 ArcSec, which shows how far away the galaxy is based on the amount of light it gives off, that there was a positive correlation between this and Log Mass, which is how massive the galaxies are. We concluded that the reason for the large amount of local density was because the red elliptical galaxies had more gravity and drew in other galaxies.

After all the research the presentation went better than what I would have thought. I remembered all the facts, and even included a few puns. My two partners in the project were very helpful and I think that they did really well in the research and presentation.  Even though we had problems going through the data we eventually figured out the numbers and raw data and refined it into a “stellar” presentation.


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