Galactic Haloes from Self-Interacting Neutrinos

The objective of this research is to provide an explanation of galactic haloes using established particles and forces using recent theoretical developments. Light fermions, with masses on the order of 1 eV/c2, are not a leading candidate for dark matter because of their large free-streaming scale length and their violation of the Tremaine-Gunn bound. With a self-interaction of fermions, the free-streaming scaling length is reduced, and the tenets of the Tremaine-Gunn bound are not applicable. Binding of neutrinos via a feeble SU(3) force is considered as a model for such interactions. The assumed sum of masses of the three neutrino flavors is 0.07 eV/c2. The resulting form of matter for such bound neutrinos is found to be a degenerate Fermi fluid. Pressure-equilibrium approaches applied to this fluid provide cuspy solutions and match observationally-inferred profiles for galactic haloes. Such approaches also match the observed total enclosed mass for galaxies similar to the Milky Way. The computed structures are found to be stable. The hypothesis is considered in view of observationally-inferred halo-halo interactions and gives results that are consistent with the observed Bullet cluster halo interaction. The theory gives agreement with observationally-inferred properties of dark matter near earth. Questions related to interaction rates, consistency with SN1987a data, the cosmic microwave background, the issue of SU(3) interactions between neutrinos and quarks, free-streaming after neutrino decoupling, and dark-matter abundance are addressed in a companion paper.

Neutron-Capture Elements in the Double-Enhanced Star HE 1305-0007： a New s- and r-Process Paradigm

The star HE 1305-0007 is a metal-poor double-enhanced star with metallicity [Fe/H] = -2.0, which is just at the upper limit of the metallicity for the observed double-enhanced stars. Using a parametric model, we find that almost all s-elements were made in a single neutron exposure. This star should be a member of a post-commonenvelope binary. After the s-process material has experienced only one neutron exposure in the nucleosynthesis region and is dredged-up to its envelope, the AGB evolution is terminated by the onset of common-envelope evolution. Based on the high radial-velocity of HE 1305-0007, we speculate that the star could be a runaway star from a binary system, in which the AIC event has occurred and produced the r-process elements.

Scientific objectives of the Hot Universe Baryon Surveyor(HUBS) mission

The Hot Universe Baryon Surveyor(HUBS) is a proposed space-based X-ray telescope for detecting X-ray emissions from the hot gas content in our universe. With its unprecedented spatially-resolved high-resolution spectroscopy and large field of view,the HUBS mission will be uniquely qualified to measure the physical and chemical properties of the hot gas in the interstellar medium, the circumgalactic medium, the intergalactic medium, and the intracluster medium. These measurements will be valuable for two key scientific goals of HUBS, namely to unravel the AGN and stellar feedback physics that governs the formation and evolution of galaxies, and to probe the baryon budget and multi-phase states from galactic to cosmological scales. In addition to these two goals, the HUBS mission will also help us solve some problems in the fields of galaxy clusters, AGNs, difuse X-ray backgrounds, supernova remnants, and compact objects. This paper discusses the perspective of advancing these fields using the HUBS telescope.

Low-α metal-rich stars with sausage kinematics in the LAMOST survey: Are they from the Gaia-Sausage-Enceladus galaxy?

We search for metal-rich Sausage-kinematic(MRSK)stars with[Fe/H]>−0.8 and−100<Vϕ<50 km/s in LAMOST DR5 in order to investigate the influence of the Gaia-Sausage-Enceladus(GSE)merger event on the Galactic disk.For the first time,we find a group of low-αMRSK stars,and classify it as a metal-rich tail of the GSE galaxy based on the chemical and kinematical properties.This group has slightly larger R_(apo),Z_(max) and Etot distributions than a previously-reported high-αgroup.Its low-αratio does not allow for an origin resulting from the splash process of the GSE merger event,as is proposed to explain the high-αgroup.A hydrodynamical simulation by Amarante et al.provides a promising solution,in which the GSE galaxy is a clumpy Milky-Way analogue that develops a bimodal disk chemistry.This scenario explains the existence of MRSK stars with both high-αand low-αratios found in this work.It is further supported by another new feature that a clump of MRSK stars is located at Z_(max)=3-5 kpc,which corresponds to the widely adopted disk-halo transition at|Z|∼4 kpc.We suggest that a pile-up of MRSK stars at Zmax contributes significantly to this disk-halo transition,an interesting imprint left by the GSE merger event.These results also provide an important implication on the connection between the GSE and the Virgo Radial Merger.