2022 Undergraduate Research Showcase

Document Type

Student Presentation

Presentation Date


Faculty Sponsor

Dr. Heidi Wu


Dark matter halos are used as cosmological probes of the universe. From the halo mass function, we can obtain energy density parameters. However, in the observation of halos there are projection effects that make it difficult to count the number of galaxies in a halo. These projection effects include uncertainty about the radius of each halo and the line of sight distance. The line of sight distance is measured from the halo center. Distances are determined with redshift. We can use simulation data so we know everything about a halo and then compare different methods of counting galaxies. For simplicity, we used a fixed line of sight distance and assumed we knew the halo center. We compared galaxy counts from catalogs using different line of sight distances, with and without percolation, and fixed vs iterative radii. Percolation is counting a galaxy towards the more massive halo when the galaxy is within the radius of multiple halos to prevent halo radii from blowing up. The catalog without percolation has more galaxies at low masses but has little effect at high halo masses. We have found that the projection effects are dominated by galaxies within 15 Mpc/h.



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