S. M. Koushiappas | Searcharxiv

arXiv2015

Dark matter annihilation and decay profiles for the Reticulum II dwarf spheroidal galaxy

The dwarf spheroidal galaxies (dSph) of the Milky Way are among the most attractive targets for indirect searches of dark matter. In this work, we reconstruct the dark matter annihilation (J-factor) and decay profiles for the newly discovered dSph Reticulum II. Using an optimized spherical Jeans analysis of kinematic data obtained from the Michigan/Magellan Fiber System (M2FS), we find Reticulum II's J-factor to be among the largest of any Milky Way dSph. We have checked the robustness of this result against several ingredients of the analysis. Unless it suffers from tidal disruption or significant inflation of its velocity dispersion from binary stars, Reticulum II may provide a unique window on dark matter particle properties.

astro-ph.HE↗

arXiv2004

Massive black hole seeds from low angular momentum material

(ABRIDGED) We present a model in which the seeds of supermassive black holes form from the lowest angular momentum gas in proto-galaxies at high redshift. We show that this leads to a correlation between black hole masses and spheroid properties, as observed today. We assume that gas in early-forming, rare halos has a distribution of specific angular momentum similar to that expected for dark matter halos. This distribution has a significant low angular momentum tail which implies that every proto-galaxy should contain gas that ends up in a high-density disc. In halos more massive than a critical threshold of \~10^8Msun, the discs are gravitationally unstable, and experience an efficient Lin-Pringle viscosity that allows mass inflow. This process continues until the first massive stars disrupt the disc. Black holes are created with a characteristic mass of ~10^5 Msun, independent of the redshift of formation. This serves as a lower bound for black-hole masses in galaxies today. The comoving mass density of black hole seeds grows with time, and saturates when cosmic reionization stops gas cooling in these low-mass systems. By z~15, the comoving mass density becomes comparable to that inferred from observations, with room for appropriate additional luminous growth during a later quasar accretion phase. Hierarchical merging after z~15 naturally leads to a linear correlation between black-hole mass and stellar spheroid mass, with negligible black hole masses in disc-dominated galaxies.

astro-ph↗