Dark Matter search in dwarf irregular galaxies with the Fermi Large Area Telescope

TL;DR

This study uses 11 years of Fermi-LAT gamma-ray data to search for dark matter signals in dwarf irregular galaxies, setting upper limits on annihilation cross-sections and exploring the impact of different dark matter profiles and substructures.

Contribution

It provides the first comprehensive gamma-ray analysis of dwarf irregular galaxies considering both cored and cuspy dark matter profiles, including halo substructures, and sets new constraints on dark matter annihilation.

Findings

No significant gamma-ray emission detected from the targets.

IC10 and NGC6822 provide the most stringent individual constraints.

Combined analysis yields the strongest limits for the $b\bar{b}$ channel at $\sim 7 \times 10^{-26}$ cm$^3$s$^{-1}$.

Abstract

We analyze 11 years of Fermi-LAT data corresponding to the sky regions of 7 dwarf irregular (dIrr) galaxies. DIrrs are dark matter (DM) dominated systems, proposed as interesting targets for the indirect search of DM with gamma rays. The galaxies represent interesting cases with a strong disagreement between the density profiles (core vs. cusp) inferred from observations and numerical simulations. In this work, we addressed the problem by considering two different DM profiles, based on both the fit to the rotation curve (in this case a Burkert cored profile) and results from N-body cosmological simulations (i.e., NFW cuspy profile). We also include halo substructures in our analysis, which is expected to boost the DM signal a factor of ten in halos such as those of dIrrs. For each DM model and dIrr, we create a spatial template of the expected DM-induced gamma-ray signal to be used in the analysis of Fermi-LAT data. No significant emission is detected from any of the targets in our sample. Thus, we compute upper limits on the DM annihilation cross-section versus mass parameter space. Among the 7 dIrrs, we find IC10 and NGC6822 to yield the most stringent individual constraints, independently of the adopted DM profile. We also produce combined DM limits for all objects in the sample, which turn out to be dominated by IC10 for all DM models and annihilation channels, i.e. $b\bar{b}$, $\tau^+\tau^-$ and $W^+W^-$. The strongest constraints are obtained for $b\bar{b}$ and are at the level of $\langle\sigma v \rangle \sim 7 \times 10^{-26}\text{cm}^{3}\text{s}^{-1}$ at $m_\chi\sim 6$ GeV. Though these limits are a factor of 3 higher than the thermal relic cross section at low WIMP masses, they are independent from and complementary to those obtained by means of other targets.