arXiv:We study the diffuse background free-free emission induc | Astronomical Informant

arXiv:We study the diffuse background free-free emission induced in dark matter halos. Since dark matter halos host ionized thermal plasma, they are an important source of the cosmological free-free emission. We evaluate the global background intensity and anisotropy of this free-free emission. We show that the dominant contribution comes from dark matter halos with a mass close to the Jeans mass, $M_{\mathrm{halo}}\sim 10^{10} M_\odot$, around the redshift $z \sim 1$. Therefore, the intensity of the free-free emission is sensitive to the small-scale curvature perturbations that form such small-mass dark matter halos. Considering the blue-tilted curvature perturbations, we find that the free-free emission signal is modified by $\sim 25 \%$ even in the parameter set of the spectral index and the running, which is consistent with the recent Planck result. However, our obtained intensity of the global and anisotropic free-free emission is smaller than the ten percent level of the observed free-free emission, which is dominated by the Galactic origin. Therefore, the measurement of the cosmological free-free signals has the potential to provide more stringent constraints on the abundance of small-mass dark matter halos and the curvature perturbations including the spectral index and the running, while carefully removing the Galactic free-free emission is required through the multifrequency radio observation or the cross-correlation study with the galaxy surveys or 21-cm intensity map.

via astro-ph updates on arXiv.org https://ift.tt/aCe8fG7