Cosmological free-free emission from dark matter halos in the $Lambda$CDM model. (arXiv:2206.11261v2 [astro-ph.CO] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Abe_K/0/1/0/all/0/1">Katsuya T. Abe</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Tashiro_H/0/1/0/all/0/1">Hiroyuki Tashiro</a>
We study the diffuse background free-free emission induced by dark matter
halos. Since dark matter halos host ionized thermal plasma, they could be an
essential source of cosmological free-free emission. We evaluate the global
background intensity and the 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
$z sim 3$. Therefore, the intensity of the free-free emission is sensitive to
the small-scale primordial curvature perturbations that form such small-mass
dark matter halos. Although our obtained intensity of the global and
anisotropic free-free emission is smaller than the $10%$ level of the
free-free emission observed in the high galactic region, we find that the
free-free emission signal is modified by $sim 20 %$ even in the parameter set
of the spectral index and the running, which is consistent with the recent
Planck result. 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.
We study the diffuse background free-free emission induced by dark matter
halos. Since dark matter halos host ionized thermal plasma, they could be an
essential source of cosmological free-free emission. We evaluate the global
background intensity and the 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
$z sim 3$. Therefore, the intensity of the free-free emission is sensitive to
the small-scale primordial curvature perturbations that form such small-mass
dark matter halos. Although our obtained intensity of the global and
anisotropic free-free emission is smaller than the $10%$ level of the
free-free emission observed in the high galactic region, we find that the
free-free emission signal is modified by $sim 20 %$ even in the parameter set
of the spectral index and the running, which is consistent with the recent
Planck result. 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.
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