ORCID Profile
0000-0001-6231-7693
Current Organisations
University of Amsterdam
,
Universiteit van Amsterdam
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Publisher: Oxford University Press (OUP)
Date: 08-09-2022
Abstract: Since the discovery of an excess in gamma rays in the direction of M31, its cause has been unclear. Published interpretations focus on dark matter or stellar related origins. Studies of a similar excess in the Milky Way centre motivate a correlation of the spatial morphology of the signal with the distribution of stellar mass in M31. However, a robust determination of the best theory for the observed excess emission is challenging due to uncertainties in the astrophysical gamma-ray foreground model. We perform a spectro-morphological analysis of the M31 gamma-ray excess using state-of-the-art templates for the distribution of stellar mass in M31 and novel astrophysical foreground models for its sky region. We construct maps for the old stellar populations of M31 based on data from the PAndAS survey and carefully remove the foreground stars. We also produce improved astrophysical foreground models via novel image inpainting techniques based on machine learning methods. Our stellar maps, mimicking the location of a population of millisecond pulsars in the bulge of M31, reach a 5.4σ significance, making them as strongly favoured as the simple phenomenological models usually considered in the literature, e.g. disc-like templates. This detection is robust to generous variations of the astrophysical foreground model. Once the stellar templates are included in the astrophysical model, we show that the dark matter annihilation interpretation of the signal is unwarranted. We demonstrate that about one million unresolved millisecond pulsars naturally explain the observed gamma-ray luminosity per stellar mass, energy spectrum, and stellar bulge-to-disc flux ratio.
Publisher: Oxford University Press (OUP)
Date: 25-07-2018
Publisher: American Physical Society (APS)
Date: 27-12-2022
Publisher: American Physical Society (APS)
Date: 02-10-2013
Publisher: Springer Science and Business Media LLC
Date: 05-09-2022
Publisher: Oxford University Press (OUP)
Date: 04-10-2022
Abstract: We introduce the TangoSIDM project, a suite of cosmological simulations of structure formation in a Λ-self-interacting dark matter (SIDM) universe. TangoSIDM explores the impact of large dark matter (DM) scattering cross-sections over dwarf galaxy scales. Motivated by DM interactions that follow a Yukawa potential, the cross-section per unit mass, σ/mχ, assumes a velocity-dependent form that avoids violations of current constraints on large scales. We demonstrate that our implementation accurately models not only core formation in haloes but also gravothermal core collapse. For central haloes in cosmological volumes, frequent DM particle collisions isotropise the particles orbit, making them largely spherical. We show that the velocity-dependent σ/mχ models produce a large ersity in the circular velocities of satellites haloes, with the spread in velocities increasing as the cross-sections reach 20, 60, and 100 cm2 g−1 in $10^9~\\rm {M}_{\\odot }$ haloes. The large variation in the haloes internal structure is driven by DM particles interactions, causing in some haloes the formation of extended cores, whereas in others gravothermal core collapse. We conclude that the SIDM models from the Tango project offer a promising explanation for the ersity in the density and velocity profiles of observed dwarf galaxies.
Location: United States of America
No related grants have been discovered for Shin'ichiro Ando.