The Supersonic Project: The eccentricity and rotational support of SIGOs and DM GHOSts

Claire E. Williams, Smadar Naoz, William Lake, Yeou S. Chiou, Blakesley Burkhart, Federico Marinacci, Mark Vogelsberger, Gen Chiaki, Yurina Nakazato, Naoki Yoshida

Submitted on 3 November 2022


A supersonic relative velocity between dark matter (DM) and baryons (the stream velocity) at the time of recombination induces the formation of low mass objects with anomalous properties in the early Universe. We widen the scope of the `Supersonic Project' paper series to include objects we term Dark Matter + Gas Halos Offset by Streaming (DM GHOSts)--diffuse, DM-enriched structures formed because of a physical offset between the centers of mass of DM and baryonic overdensities. We present an updated numerical investigation of DM GHOSts and Supersonically Induced Gas Objects (SIGOs), including the effects of molecular cooling, in high resolution hydrodynamic simulations using the AREPO code. Supplemented by an analytical understanding of their ellipsoidal gravitational potentials, we study the population-level properties of these objects, characterizing their morphology, spin, radial mass, and velocity distributions in comparison to classical structures in non-streaming regions. The stream velocity causes deviations from sphericity in both the gas and DM components and lends greater rotational support to the gas. Low mass (<∼105.5 M) objects in regions of streaming demonstrate core-like rotation and mass profiles. Anomalies in the rotation and morphology of DM GHOSts could represent an early Universe analogue to observed ultra-faint dwarf galaxies with variations in DM content and unusual rotation curves.


Comment: 26 pages, 20 figures

Subject: Astrophysics - Astrophysics of Galaxies


Projected gas (left) and dark matter (DM) (right) density around several DM GHOSts and a SIGO in a region $5$ physical kpc on a side. { The SIGO is bounded by the white ellipse, located in a region relatively devoid of dark matter, and contains no DM component. It is embedded in a stream of gas. The DM GHOSts (A, B, C, and D) each contain a gaseous and a DM component. The gas components of the DM GHOSts are shown in orange, whereas the DM components of the DM GHOSts are shown in green. Note that the DM components are not entirely spherical. The centers of mass of the gas components of A, C, and D are offset from the centers of mass of the DM component, whereas B has had time for the gas component to fall back into the center of the DM potential. Several DM halos with no associated gas components also lie in this region--depicted in pink. One of these may be the ``parent" halo of the SIGO. }