Theoretical predictions for dark matter detection in dwarf irregular galaxies with gamma rays

Abstract

We investigate rotationally supported dwarf irregular (DIRR) galaxies as a new category of targets for indirect dark matter (DM) searches with gamma-ray telescopes. In the framework of pointlike analysis, pressure-supported dwarf spheroidal (DSPH) galaxies are usually considered as one of the best categories of targets for indirect DM searches, due to their close distance and negligible astrophysical background. Nonetheless, as a result of their uncertain kinematics, the DM content and astrophysical J-factors of DSPHs are usually affected by significant errors. In this paper, we study a sample of 36 DIRRs as prospective targets of interest. In the framework of the universal rotation curve, the kinematics of DIRR galaxies provides a good estimation of their DM halo density distribution and, consequently, of their astrophysical J-factors. We calculate the J-factors for these 36 DIRR galaxies, whose kinematics have been studied in a previous work. We find a range of values comparable with the J-factors of DSPH galaxies. However, differently from DSPHs an extra astrophysical gamma-ray background component is expected in DIRR galaxies, that is due to their star-formation activity. In this paper, we show via a theoretical approach that for galaxies in our sample the extra astrophysical background component is negligible. Therefore, we conclude that DIRR galaxies can be potentially considered as additional pointlike targets for DM searches with gamma rays. As a first application of this study, we show the sensitivity limits of the Fermi-LAT telescope to these objects and we calculate constraints on the DM particle mass and annihilation cross section. We conclude that the results of the individual study of several DIRR galaxies are not yet competitive with respect to the analysis of one of the most promising DSPH galaxies, i.e., SEGUE1. However, taking into account SEGUE1's symmetry-related uncertainties in the J-factor calculation might alter this conclusion. Additionally, we calculate constraints for the combined analysis of the seven most promising DIRR galaxies of our sample.