Learned a core-cusp problem.
The core-cusp problem is one of the problem of Lambda CDM model in small scales. The simulation suggests that dark matter density profile follows models which density is proportional to r^(-1), meaning that it diverges at r = 0, e.g. NFW, Harnquist etc… Such small scale diverging structure is called ‘cusp’. However, the observation shows that galaxies have a core structure which has constant density at small scales. This mismatch between observation and simulation is called ‘Core-cusp problem’.
Yesterday, the paper about this problem was published(https://arxiv.org/abs/1707.06303). This paper discusses whether dwarf galaxies, which is galaxies strongly dominated by dark matter, have cusp structures or not, I do not still finish reading though(7/22 14:10).
To understand the background of this paper, I learned the situation of the core-cusp problem. There are the solutions by considering the different dark matter models from CDM, e.g. WDM or SIDM. But here I focus on the solutions with baryon physics in the LCDM framework. There seems to be 4 solutions. The key point is to inject energy or angular momentum to dark matter.
1. Let the gas spread from the center by supernovae. They would come back to the center after being pressure equilibrium. If repeat this process adiabatically, dark matter (+ baryon) potential would get large and form the core.(arXiv:1106.0499v2)
2. Let galaxies form disks and expel the disks by supernovae (only once). Then, dark matter gets left angular momenta, which they got when disk was formed.(J F.Navarro et al. MNRAS 283, L72-78, 1996)
3. Consider dynamical friction of the central gas. When the gas loses the energy by the friction, dark matter gets the energy due to the energy conservation. (AMR EL ZANT et al. Apj 560:636-643, 2001)
4. Inject the angular momentum to dark matter through the bar structure of galaxies. (M D.Weingberg and N. Katz Apj 580:627-633, 2002)
I don’t fully understand the mechanism of 3 and 4. Therefore, further study is recquired. Also, I’m interested in the solutions by SIDM.