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Improved constraints from ultra-faint dwarf galaxies on primordial black holes as dark matter

Stegmann, Jakob, Capelo, Pedro R, Bortolas, Elisa and Mayer, Lucio 2020. Improved constraints from ultra-faint dwarf galaxies on primordial black holes as dark matter. Monthly Notices of the Royal Astronomical Society 492 (4) , pp. 5247-5260. 10.1093/mnras/staa170

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Soon after the recent first ever detection of gravitational waves from merging black holes it has been suggested that their origin is primordial. Appealingly, a sufficient number of primordial black holes (PBHs) could also partially or entirely constitute the dark matter (DM) in our Universe. However, recent studies on PBHs in ultra-faint dwarf galaxies (UFDGs) suggest that they would dynamically heat up the stellar component due to two-body relaxation processes. From the comparison with the observed stellar velocity dispersions and the stellar half-light radii, it was claimed that only PBHs with masses ≲10M⊙ can significantly contribute to the DM. In this work, we improve the latter constraints by considering the largest observational sample of UFDGs and by allowing the PBH masses to follow an extended (lognormal) distribution. By means of collisional Fokker–Planck simulations, we explore a wide parameter space of UFDGs containing PBHs. The analysis of the half-light radii and velocity dispersions resulting from the simulations leads to three general findings that exclude PBHs with masses ∼O(1-100)M⊙ from constituting all of the DM: (i) we identify a critical sub-sample of UFDGs that only allows for ∼O(1)M⊙ PBH masses; (ii) for any PBH mass, there is an UFDG in our sample that disfavours it; (iii) the spatial extensions of a majority of simulated UFDGs containing PBHs are too large to match the observed.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Physics and Astronomy
Publisher: Oxford University Press
ISSN: 0035-8711
Date of First Compliant Deposit: 4 December 2020
Date of Acceptance: 16 January 2020
Last Modified: 10 Feb 2024 02:31

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