Impact of axisymmetric mass models for dwarf spheroidal galaxies on indirect dark matter searches

TL;DR

This study analyzes gamma-ray data from dwarf spheroidal galaxies using axisymmetric dark matter profiles, revealing that such profiles can significantly alter constraints on dark matter annihilation signals compared to traditional NFW models.

Contribution

It introduces the use of observationally-motivated axisymmetric density profiles for dwarf galaxies in dark matter searches, highlighting their impact on gamma-ray constraints.

Findings

Axisymmetric profiles often suggest cored density distributions.

Upper limits on dark matter annihilation are higher with axisymmetric models.

Using realistic profiles avoids overestimating dark matter constraints.

Abstract

Dwarf spheroidals are low-luminosity satellite galaxies of the Milky Way highly dominated by dark matter (DM). Therefore, they are prime targets to search for signals from dark matter annihilation using gamma-ray observations. While the typical assumption is that the dark matter density profile of these satellite galaxies can be described by a spherical symmetric Navarro-Frenk-White (NFW) profile, recent observational data of stellar kinematics suggest that the DM halos around these galaxies are better described by axisymmetric profiles. Motivated by such evidence, we analyse about seven years of PASS8 Fermi data for seven classical dwarf galaxies, including Draco, adopting both the widely used NFW profile and observationally-motivated axisymmetric density profiles. For four of the selected dwarfs (Sextans, Carina, Sculptor and Fornax) axisymmetric mass models suggest a cored density profile rather than the commonly adopted cusped profile. We found that upper limits on the annihilation cross section for some of these dwarfs are significantly higher than the ones achieved using an NFW profile. Therefore, upper limits in the literature obtained using spherical symmetric cusped profiles, such as the NFW, might be overestimated. Our results show that it is extremely important to use observationally motivated density profiles going beyond the usually adopted NFW in order to obtain accurate constraints on the dark matter annihilation cross section.