Effect of Black Holes in Local Dwarf Spheroidal Galaxies on Gamma-Ray Constraints on Dark Matter Annihilation

TL;DR

This paper investigates how the presence of black holes in dwarf spheroidal galaxies affects gamma-ray constraints on dark matter annihilation, showing that black holes can significantly tighten these limits and impact dark matter interpretations.

Contribution

It introduces models for black hole effects on dark matter profiles in dwarf galaxies and assesses their impact on gamma-ray constraints on dark matter properties.

Findings

Black holes can enhance dark matter annihilation constraints by up to a factor of 10^6.

Presence of black holes in dwarfs can rule out the dark matter explanation for the Galactic center gamma-ray excess.

Wino dark matter up to 3 TeV and thermal relic WIMPs above 100 GeV are constrained by these effects.

Abstract

Recent discoveries of optical signatures of black holes in dwarf galaxies indicates that low-mass galaxies can indeed host intermediate massive black holes. This motivates the assessment of the resulting effect on the host dark matter density profile, and the consequences for the constraints on the plane of the dark matter annihilation cross section versus mass, stemming from the non-observation of gamma rays from local dwarf spheroidals with the Fermi Large Area Telescope. We compute the density profile using three different prescriptions for the black hole mass associated with a given spheroidal galaxy, and taking into account the cutoff to the density from dark matter pair-annihilation. We find that the limits on the dark matter annihilation rate from observations of individual dwarfs are enhanced by factors of a few up to $10^6$, depending on the specific galaxy, on the black hole mass prescription, and on the dark matter particle mass. We estimate limits from combined observations of a sample of 15 dwarfs, for a variety of assumptions on the dwarf black hole mass and on the dark matter density profile prior to adiabatic contraction. We find that if black holes are indeed present in local dwarf spheroidals, then, independent of assumptions, (i) the dark matter interpretation of the Galactic center gamma-ray excess would be conclusively ruled out, (ii) wino dark matter would be excluded up to masses of about 3 TeV, and (iii) vanilla thermal relic WIMPs must be heavier than 100 GeV.