Evolution of Compact Stellar Systems in Ultralight Dark Matter Halos: Dependence on Stellar and Dark Matter Parameters

Abstract

Compact stellar systems are often used to place stringent constraints on the particle mass of ultralight dark matter (ULDM), as the heating effect induced by wave interference can drive system expansion, potentially bringing them into tension with observations. In a recent study, we pointed out that internal two-body relaxation in these stellar systems may have a significant impact on their evolution in ULDM halos, an effect overlooked in previous studies. Here, we further investigate the influence of stellar metallicity, the Milky Way's tidal field, and the ULDM particle mass on the long-term fate of compact stellar populations. We find that metal-richer systems are generally more resistant to disruption. The tidal field of the Milky Way, by altering the orbital motion of the stellar systems within host ULDM halos, can significantly affect their stability. Furthermore, we find in our simulations that the heating effect becomes stronger with increasing ULDM particle mass when the system size is much smaller than the ULDM de Broglie wavelength $R_{\rm h} \ll \lambda_{\rm dB} $, in contrast to the $\lambda_{\rm dB}\lesssim R_{\rm h}$ case. These results highlight the complexity of the evolution of compact stellar systems in ULDM halos, and suggest that existing constraints derived from the systems, such as ultrafaint dwarf galaxies, may require careful revision.