92 Understanding the Radial Distribution of Dwarf Satellite Galaxies Beyond the Virial Radii

Faculty Mentor: Yao-Yuan Mao (Physics and Astronomy, University of Utah)

Dark matter has been theorized to exist for over 80 years based on astronomical observations but has yet to be found in terrestrial experiments. Named for its lack of interaction with the electromagnetic field, dark matter does not absorb, reflect, or emit electromagnetic radiation making it undetectable to us. As such, it is considered one of the greatest unsolved mysteries in astronomy. However, visible galaxies are believed to live inside dark matter halos, which are high-density regions of dark matter that have disassociated themselves from the cosmological constant and contain matter bound together through gravity. Studies of these visible galaxies can hence reveal the distribution of dark matter within these halos. Smaller galaxies that hold fewer stars and mass, commonly known as dwarf galaxies, are of particular interest as they are rich in dark matter. These dwarf galaxies are sometimes close enough to another galaxy to be pulled into the gravity of the larger “host” galaxy which then makes them a satellite in the host’s system.

My work uses cosmological simulations to study the spatial distribution of dwarf galaxies within and outside of their individual host systems to better understand the underlying dynamics within the structure of dark matter halos. The existing body of observational studies predominantly concentrates on host galaxy systems up to the virial radius, as exemplified in studies of our own Milky Way satellites and research such as “The Satellites Around Galactic Analogs Survey II” (Mao et al.,2021). We use the Very Small MultiDark Planck Simulation (VSMDPL) to make predictions of the expected number of dwarf galaxies one could find in the outskirts of the halo, and to study its correlation with the number of satellite galaxies (within virial radius) and other host halo properties.

We have found that the number of satellite galaxies within our selected inner and outer regions is not as strongly correlated as expected. We also found that the number of galaxies (halos) as a function of radial distance to the host, known as the radial profile, correlates differently with different host properties. In particular, by calculating the correlation strength at multiple radii, we found that the number of subhalos within the virial radius does not always correlate the strongest with a host property. Our finding also demonstrates the halo assembly bias effect becomes significant at approximately 1 Mpc away from the host galaxies. Our analysis will help connect the study of satellite systems to studies about the outskirts of host halos (e.g., splashback radii and assembly bias) and will be influential in predicting the next stage of observational data that will be conducted in the future.

References

Mao, Y.-Y., (2021) The SAGA Survey. II. Building a statistical sample of satellite systems around Milky Way-like galaxies, The Astrophysical Journal, vol. 907, no. 2. doi:10.3847/1538-4357/abce58.