Halo heating from fluctuating gas in a model dwarf

Mahmoud Hashim, Amr A. El-Zant*, Jonathan Freundlich, Justin I. Read, Françoise Combes

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


The cold dark matter (CDM) structure formation scenario faces challenges on (sub)galactic scales, central among them being the ‘cusp-core’ problem. A known remedy, driving CDM out of Galactic Centres, invokes interactions with baryons, through fluctuations in the gravitational potential arising from feedback or orbiting clumps of gas or stars. Here, we interpret core formation in a hydrodynamic simulation in terms of a theoretical formulation, which may be considered a generalization of Chandrasekhar’s theory of two body relaxation to the case when the density fluctuations do not arise from white noise; it presents a simple characterization of the effects of complex hydrodynamics and ‘subgrid physics’. The power spectrum of gaseous fluctuations is found to follow a power law over a range of scales, appropriate for a fully turbulent compressible medium. The potential fluctuations leading to core formation are nearly normally distributed, which allows for the energy transfer leading to core formation to be described as a standard diffusion process, initially increasing the velocity dispersion of test particles as in Chandrasekhar’s theory. We calculate the energy transfer from the fluctuating gas to the halo and find it consistent with theoretical expectations. We also examine how the initial kinetic energy input to halo particles is redistributed to form a core. The temporal mass decrease inside the forming core may be fit by an exponential form; a simple prescription based on our model associates the characteristic time-scale with an energy relaxation time. We compare the resulting theoretical density distribution with that in the simulation.

Original languageEnglish
Pages (from-to)772-789
Number of pages18
JournalMonthly Notices of the Royal Astronomical Society
Issue number1
StatePublished - 1 May 2023
Externally publishedYes


  • dark matter
  • galaxies: evolution
  • galaxies: haloes


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