Probing signals of self-interacting dark matter core collapse in Hi-rich galaxies
Probing signals of self-interacting dark matter core collapse in Hi-rich galaxies
Probing Signals of Self-Interacting Dark Matter Core Collapse in Hi-Rich Galaxies
Dark matter remains one of the most enigmatic components of our universe. Although it constitutes approximately 27% of the total cosmic mass-energy budget, its nature continues to elude direct detection. Traditional cold dark matter (CDM) models have successfully explained the large-scale structure of the universe, yet they often face challenges on galactic and sub-galactic scales, such as the "core-cusp" and "too-big-to-fail" problems. One promising alternative is Self-Interacting Dark Matter (SIDM)—a theoretical model proposing that dark matter particles can scatter off each other with significant cross-sections, leading to observable differences in galactic structure.
A particularly intriguing prediction of SIDM is the phenomenon of core collapse, where dark matter halos that were once cored due to particle interactions can become denser and more cuspy over time. This dynamic process depends heavily on the thermal and mass distribution in galaxies, making observational signatures of such collapses difficult to identify. However, recent studies suggest that Hi-rich galaxies—those abundant in neutral hydrogen gas (Hi)—offer a promising laboratory to probe these effects.
Hi-rich galaxies, due to their extended gas distributions and relatively undisturbed rotational dynamics, can serve as excellent tracers of gravitational potential. The 21 cm line emission from neutral hydrogen provides high-resolution data on the distribution and motion of gas, which, in turn, reflects the underlying dark matter halo profile. In SIDM scenarios, one would expect these galaxies to show distinct kinematic features compared to CDM predictions—such as contracted rotation curves, central mass deficits, or even an observable contraction of the Hi disk.
Recent simulations have modeled the evolution of SIDM halos in such gas-rich systems and predict that core collapse may result in unusually steep inner rotation curves or irregular Hi morphologies in low-mass galaxies. These deviations can be directly compared with data from surveys such as ALFALFA, THINGS, LITTLE THINGS, and future SKA observations. Furthermore, galaxies in low-density environments, where external interactions are minimal, provide ideal conditions to isolate the intrinsic effects of SIDM.
Another signature of SIDM-induced core collapse may lie in asymmetries in Hi velocity fields or in the existence of dark-matter-dominated galaxies with unexpectedly compact cores. These effects might be subtle, but when combined across a population of galaxies, they could present statistically significant deviations from CDM expectations. Additionally, SIDM can influence the baryonic feedback cycle, altering star formation efficiency and the regulation of galactic winds, which in turn shapes the galaxy’s morphology and kinematics.
The challenge remains in disentangling SIDM effects from those of baryonic processes, which can also modify dark matter distributions via feedback mechanisms. However, the synergy between observational data and SIDM-focused simulations is becoming increasingly powerful, offering the potential to test SIDM hypotheses in statistically meaningful ways. Future high-resolution radio surveys and integral field spectroscopy of Hi-rich systems will be key in this endeavor.
In conclusion, while CDM has served as the backbone of our cosmological understanding for decades, SIDM presents a viable alternative that resolves several small-scale anomalies. The study of Hi-rich galaxies, especially in the context of core collapse, provides a unique opportunity to put these models to the test. As our observational capabilities continue to grow, the coming decade promises significant strides in our quest to uncover the true nature of dark matter.
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