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Astrophysics > Cosmology and Nongalactic Astrophysics

arXiv:2108.01916 (astro-ph)
[Submitted on 4 Aug 2021 (v1), last revised 8 Sep 2021 (this version, v2)]

Title:Free-free background radiation from accreting primordial black holes

Authors:Hiroyuki Tashiro, Katsuya T. Abe, Teppei Minoda
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Abstract:Baryonic gas falling onto a primordial black hole (PBH) emits photons via the free-free process. These photons can contribute the diffuse free-free background radiation in the frequency range of the cosmic microwave background radiation (CMB). We show that the intensity of the free-free background radiation from PBHs depends on the mass and abundance of PBHs. In particular, considering the growth of a dark matter (DM) halo around a PBH by non-PBH DM particles strongly enhances the free-free background radiation. Large PBH fraction increase the signal of the free-free emission. However, large PBH fraction also can heat the IGM gas and, accordingly, suppresses the accretion rate. As a result, the free-free emission decreases when the PBH fraction is larger than 0.1. We find that the free-free emission from PBHs in the CMB and radio frequency is much lower than the CMB blackbody spectrum and the observed free-free emission component in the background radiation. Therefore, it is difficult to obtain the constraint from the free-free emission observation. However further theoretical understanding and observation on the free-free emission from cosmological origin is helpful to study the PBH abundance with the stellar mass.
Comments: 7 pages, 6 figures. In this version, we have fixed a bug that resulted in the overestimation of free-free signals. The conclusions have been updated
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Phenomenology (hep-ph)
Cite as: arXiv:2108.01916 [astro-ph.CO]
  (or arXiv:2108.01916v2 [astro-ph.CO] for this version)
  https://doi.org/10.48550/arXiv.2108.01916

Submission history

From: Hiroyuki Tashiro [view email]
[v1] Wed, 4 Aug 2021 09:04:20 UTC (53 KB)
[v2] Wed, 8 Sep 2021 00:57:00 UTC (61 KB)
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