Determination of dark matter distribution in Ursa Major III and constraints on dark matter annihilation

TL;DR

This paper analyzes the dark matter distribution in Ursa Major III using stellar data and gamma-ray observations to set constraints on dark matter annihilation, highlighting the importance of member star identification.

Contribution

It provides the first detailed dark matter density profile and J-factor calculations for Ursa Major III, considering different annihilation scenarios and the impact of star membership selection.

Findings

J-factors vary significantly with star membership criteria.

Constraints on dark matter annihilation cross sections are weaker when excluding outliers.

J-factors are sensitive to the inclusion of velocity outliers.

Abstract

The recently discovered satellite dwarf galaxy Ursa Major III provides a promising opportunity to explore the signatures resulting from dark matter (DM) annihilation, due to its proximity and large J-factor. Owing to the absence of an excess of $\gamma$-ray signatures originating from Ursa Major III, observations of $\gamma$-rays, such as those from Fermi-LAT, can be utilized to set constraints on the DM annihilation cross section. In this study, we determine the DM density profile, and consider the relationship between DM density and velocity dispersion at different locations within Ursa Major III through Jeans analysis. We calculate the J-factor of Ursa Major III for s-wave annihilation, along with the effective J-factors for p-wave and Sommerfeld enhanced annihilation scenarios. Utilizing these derived J-factors, we set stringent constraints on DM annihilation cross sections in three scenarios. Given the substantial impact of member star identification on the J-factor of Ursa Major III, we further calculate J-factors with the condition of excluding the largest velocity outlier. Our analysis reveals a notable reduction in the median value and an increase in the deviation of J-factors, thereby leading to considerably weaker constraints.