Unexpected clustering pattern in dwarf galaxies challenges formation models.

Area of Science:

• Cosmology
• Galaxy Formation
• Dark Matter Physics

Background:

• Galaxy clustering reveals insights into cosmology, galaxy formation, and dark matter.
• Massive, red, compact galaxies typically exhibit stronger spatial clustering.
• This clustering is generally explained by galaxy formation within cold dark matter (CDM) halos of varying mass and assembly history.

Purpose of the Study:

• To investigate the unexpectedly strong large-scale clustering of isolated, diffuse, blue dwarf galaxies.
• To reconcile these observations with existing cosmological models and explore alternative dark matter scenarios.

Main Methods:

• Analysis of galaxy clustering using observational data.
• Comparison of observed clustering with predictions from simulations within the standard Lambda Cold Dark Matter (ΛCDM) cosmology.
• Evaluation of galaxy evolution models and self-interacting dark matter (SIDM) scenarios.

Main Results:

• Isolated, diffuse, blue dwarf galaxies show unexpectedly strong large-scale clustering, comparable to massive galaxy groups.
• This clustering is significantly stronger than predicted based on their halo mass alone.
• The observed pattern aligns with halo assembly bias in ΛCDM simulations only if diffuse dwarfs formed in low-mass, older halos.

Conclusions:

• Current galaxy evolution models within the ΛCDM framework do not reproduce the observed dwarf galaxy clustering.
• The findings suggest that dwarf galaxy formation in low-mass, older halos is key to understanding this phenomenon.
• Self-interacting dark matter provides a viable explanation for the observed strong clustering, warranting further consideration.