#8: Galaxy Alignment, Galaxy Clusters, & The Biggest Structures in the Universe

Hello, reader! I'm back from spring break and ready to explore parts of astrophysics related to galaxy orientation. Today I'll be walking through a research article I found back in December. The article is titled "Galaxy Alignments As A Probe Of The Dynamical State Of Clusters" and discusses galaxy cluster alignments and what this information can tell us about these clusters and their individual members.

You can find my highlighted version of the article here. Pink is for information I do not understand, orange is for conclusions that interest me or seem relevant, and purple is for information that I thought would provide insight to my senior project.

Here is a summary of the points I found the most interesting and insightful, and how they connect to my project and/or my interests.

• The younger a cluster is, the stronger galaxy alignments are.​

• ​Several of the galaxies I analyzed for COSMOS are relatively young. If their orientations are for the most part similar (if not the same), then this finding could explain that phenomenon.

• There is an alignment relationship between nearby clusters and the brightest cluster galaxy

• ​Luminosity is a value I measured when determining galaxies' dark matter content, and it was interesting to note that luminosity also related to orientation in a way I hadn't previously thought of.

• Substructures in clusters are aligned with cluster orientation and along large scale filamentary structures within which they're embedded.

• ​I did not know there were substructures within clusters, so reading this made me very curious about the nature of substructures. When attempting to gain some general knowledge about this subject, I stumbled across this paper which discusses the alignment of dark matter halos with galaxy clusters. This topic would contribute to my understanding of my project and I am now looking into this topic in greater detail. Expect a post about this research article in a few days.

• The filamentary structures being referred to are the largest structures in the universe (which is, in my opinion, one of the coolest parts about my project). They are giant thread-like formations that define the boundaries between large voids in the universe. At an initial glance, this topic seems to relate to some concepts I encountered when reading Max Tegmark's book Our Mathematical Universe. In his book, Tegmark explained that the structure of the overall universe stems from quantum fluctuations that were occurring when the universe was extremely small and expanding extremely quickly (a period known as inflation). While the nature of filamentary structures isn't a topic that was greatly explored in this research article, I am extremely excited to learn more about filamentary structures over the next few days.

• Cluster - cluster and subcluster - cluster alignments occur naturally in the cold dark matter model.

• ​The standard model includes these results, making them anticipated and thus accepted.

• In older / more "relaxed" galaxy clusters there is less alignment between components of the cluster. The existence or not of galaxy alignments could indicate a galaxy's or cluster's dynamical state.

• ​This finding illustrates the importance of analyzing the orientation of galaxies (which was the original goal of my project). Analyzing the orientation of original galaxies allows one to determine the age of the cluster itself, and thus the cluster's overall "age" and state.

• There is no clear conclusion in attempting to find intrinsic alignments of galaxies or clusters.

• ​There's no "default" position for these galaxies or clusters - I would have been surprised if there was a "default" position for either of these objects.

Reader, I hope you also experience the same joy and excitement I felt when reading this article for the first time. While I certainly did not understand everything in the article (a fact corroborated by the large amounts of text that's highlighted pink) it was exciting to read about the paper's findings and think about how this paper connects back to my interests in dark matter and galaxy orientation.

As always, I greatly appreciate any questions or feedback. Until next time, reader.

#update #technical