The impact of galaxy orientation on neighbour galaxy counts

Alam, Afrida

Abstract

We utilised data from Galaxy Zoo, Sloan Digital Sky Survey and Yang et al. (2007) catalogue to determine if a galaxy’s orientation, i.e. whether it is viewed edge-on or face-on, impacts the number of observed neighbour galaxies. The results showed that there is an excess of neighbours for edge-on galaxies than for face-on galaxies, once parameters such as halo mass and average stellar mass were controlled. For edge-on galaxies, the mean count and median of neighbours were 31.78 and 16.00, with lower and upper quartiles of 5.00 and 40.00. For face-on galaxies, the mean count and median were 12.88 and 10.00, with lower and upper quartiles of 6.00 and 16.00. This indicates that this an observational bias rather than a physical effect and face-on galaxies obscure their neighbours leading to fewer detections.
This result could have consequences for the unified theory of active galactic nuclei (AGN) which states that the difference between Type 1 and Type 2 AGN is a line-of-sight effect relative to an observer and their environments should not differ. However, studies have observed an excess of neighbours around Type 2 AGN compared to Type 1 AGN.We conducted a preliminary test to determine whether this excess is observed when separating the sample by Type 1 and Type 2. The results showed that for Type 1 AGN, the mean count and median of neighbours were 30.91 and 18.00 for edge-on galaxies, and 12.64 and 10.00 for face-on galaxies. For Type 2 AGN, the mean count and median were 24.50 and 10.00 for edge-on galaxies, and 12.25 and 8.50 for face-on galaxies. Therefore, there is an excess of neighbours for edge-on galaxies than for face-on galaxies in both Type 1 and Type 2 AGN. Future works could look at whether we could attribute this excess to edge-on galaxies being more likely to be associated with Type 2 AGN.

Citation

Alam, A. (2021). The impact of galaxy orientation on neighbour galaxy counts. (Thesis). University of Hull. Retrieved from https://hull-repository.worktribe.com/output/4224279

• Thesis Type: Thesis
• Deposit Date: Aug 2, 2022
• Publicly Available Date: Feb 24, 2023
• Keywords: Physics
• Public URL: https://hull-repository.worktribe.com/output/4224279
• Additional Information: Department of Physics and Mathematics, The University of Hull
• Award Date: Aug 1, 2021