Halo formation and evolution in scalar field dark matter and cold dark matter
- Author(s)
- Horst Foidl, Tanja Rindler-Daller, Werner W. Zeilinger
- Abstract
We present dark matter (DM)-only simulations of halo formation and evolution in scalar field dark matter (SFDM) cosmologies in the Thomas-Fermi regime, also known as "SFDM-TF,"where a strong repulsive two-particle self-interaction (SI) is included. This model is a valuable alternative to cold dark matter (CDM), with the potential to resolve the "cusp-core"problem of the latter. In general, SFDM behaves like a quantum fluid. Previous literature has presented fluid approximations for SFDM-TF in 1D and 3D, respectively, as well as numerical DM-only simulations of SFDM-TF halo formation, whose results are in agreement with earlier analytic expectations, that a core-envelope halo structure arises; a central region close to a (n=1)-polytropic core, surrounded by a CDM-like [i.e. Navarro-Frenk-White (NFW)-like] halo envelope. While those previous results are generally in mutual agreement, discrepancies have been also reported. Therefore, we perform dedicated 3D cosmological simulations of the halo infall problem for the SFDM-TF model, as well as for CDM and its corresponding CDM fluid approximation, where we implement both previous fluid approximations into the code ramses. We compare our findings with those previous simulations. Our results are very well in accordance with previous works and extend upon them, in that we can explain the reported discrepancies. They are not due to the different fluid approximations, nor the geometry, but rather a result of different simulation setups. Moreover, we find some interesting details, as follows. The evolution of both SFDM-TF and CDM halos follows a two-stage process. In the early stage, the central density in the halo rises, its profile becomes close to a (n=1.5)-polytropic core being dominated by an "effective"velocity-dispersion pressure Pσ that stabilizes it against gravity. In fact, this pressure stems from random orbital motion in CDM, but from random wave motion in SFDM. Consecutively, for CDM halos, this core transitions into a steep central cusp whose slope is almost the same as the outer density slope, which is close to ρ∝r-3 as expected from Navarro-Frenk-White (NFW). Finally, however, the central profile makes another transition to a "shallower cusp,"very close to the NFW behavior of ρ∝r-1. On the other hand, in the formation of the SFDM-TF halo, the additional pressure PSI due to SI determines the second stage of the evolution. At the end, PSI dominates in the central region, whose density follows closely a (n=1)-polytropic core. This core is enshrouded by a nearly isothermal envelope, i.e. the outskirts are similar to CDM at this point. We also encounter a new effect in our simulations, namely a late-time expansion of both polytropic core plus envelope, because the size of the almost isothermal halo envelope is affected by the external pressure, which decreases with the expansion of the background universe. Hence, the core size of SFDM-TF halos is not necessarily determined only by the parameters of the model, as our simulations reveal that an initial primordial core of ∼100 pc - demanded by power spectrum constraints - can evolve into a larger core of ≳1 kpc, after all, during halo evolution, even without feedback from baryons.
- Organisation(s)
- Department of Astrophysics
- External organisation(s)
- Wolfgang Pauli Institut, University of Vienna
- Journal
- Physical Review D
- Volume
- 108
- No. of pages
- 26
- ISSN
- 2470-0010
- DOI
- https://doi.org/10.1103/PhysRevD.108.043012
- Publication date
- 08-2023
- Peer reviewed
- Yes
- Austrian Fields of Science 2012
- 103003 Astronomy, 103004 Astrophysics
- ASJC Scopus subject areas
- Nuclear and High Energy Physics
- Portal url
- https://ucrisportal.univie.ac.at/en/publications/16161aeb-0537-453d-bd9d-e74d8b356d18