Sunyaev-Zel'dovich effects from annihilating dark matter in the Milky Way: Smooth halo, subhalos, and intermediate-mass black holes

We study the Sunyaev-Zel’dovich effect potentially generated by relativistic electrons injected from dark matter annihilation or decay in the Galaxy, and check whether it could be observed by Planck or the Atacama Large Millimeter Array (ALMA), or even imprint the current CMB data as, e.g., the specific fluctuation excess claimed from an recent reanalysis of the WMAP-5 data. We focus on high-latitude regions to avoid contamination of the Galactic astrophysical electron foreground, and consider the annihilation or decay coming from the smooth dark matter halo as well as from subhalos, further extending our analysis to a generic modeling of spikes arising around intermediate-mass black holes. We show that all these dark Galactic components are unlikely to produce any observable Sunyaev-Zel’dovich effect. For a self-annihilating dark matter particle of 10 GeV with canonical properties, the largest optical depth we find is τe≲10-7 for massive isolated subhalos hosting intermediate-mass black holes. We conclude that dark matter annihilation or decay on the Galactic scale cannot lead to significant Sunyaev-Zel’dovich distortions of the CMB spectrum.