Interaction of clumpy dark matter with interstellar medium in astrophysical systems

TL;DR

This paper investigates how clumpy dark matter interacts with interstellar gas, affecting galaxy formation and the distribution of dark matter structures, with implications for indirect detection experiments.

Contribution

It provides a detailed analysis of momentum exchange between gas streams and clumpy dark matter, highlighting its role in galaxy formation and dark matter distribution.

Findings

Effect increases with clump mass, influencing momentum exchange.

Ineffective in galaxy or cluster collisions.

Significant during galaxy formation, leading to a more clumpy, oblate dark matter substructure.

Abstract

Contemporary cosmological conceptions suggest that the dark matter in haloes of galaxies and galaxy clusters has most likely a clumpy structure. If a stream of gas penetrates through it, a small-scale gravitational field created by the clumps disturbs the flow resulting in momentum exchange between the stream and the dark matter. In this article, we perform an analysis of this effect, based on the hierarchial halo model of the dark matter structure and Navarro-Frenk-White density profiles. We consider the clumps of various masses, from the smallest up to the highest ones $M\ge 10^{9} M_\odot$. It has been found that in any event the effect grows with the mass of the clump: not only the drag force $\mathfrak F$ acting on the clump, but also its acceleration $w=\mathfrak F/M$ increases. We discuss various astrophysical systems. The mechanism proved to be ineffective in the case of galaxy or galaxy cluster collisions. On the other hand, it played an important role during the process of galaxy formation. As a result, the dark matter should have formed a more compact, oblate, and faster rotating substructure in the halo of our Galaxy. We have shown that this thick disk should be more clumpy than the halo. This fact is very important for the indirect detection experiments since it is the clumps that give the main contribution to the annihilation signal. Our calculations show that the mechanism of momentum exchange between the dark and baryon matter is ineffective on the outskirts of the galactic halo. It means that the clumps from there were not transported to the thick disk, and this regions should be more clumpy than the halo on the average.