Lunch talk on Jun. 30, 2025

Small scale challenges of ΛCDM

Speaker: Huijie Hu (UCAS)

Venue: SWIFAR Building 2111

Time: 12:45 PM, Monday, Jun. 30, 2025

Abstract: 

The standard galaxy formation model under the Lambda-cold dark matter (ΛCDM) cosmological paradigm has successfully reproduced the large-scale structure of galaxies and the properties of massive galaxies in observations. However, researchers have found lots of discrepancies between simulations and observations at small scales, which are called small-scale challenges, such as the missing satellite galaxies and the “too big to fail” problems. My research mainly focus on two newly discovered small-scale challenges. We have found 19 dark-matter-deficient dwarf galaxies, 14 of them reside in isolated environment where their formation and evolution are free from the environment. Such kind of system challenges the current galaxy formation theory and could also provide new clues for the nature of dark matter (e.g., warm dark matter, fuzzy dark matter, self-interacting dark matter, or MOND). We use 88 HI-rich UDGs (HUDGs) from ALFALFA to investigate one of the dynamical scaling relations at low mass end, the baryonic Tully-Fisher relation (BTFR). We found that the HUDGs deviate from the BTFR, and the deviation of HUDGs from the BTFR is more significant than that from the TFR. Our result indicates that a high-gas fraction may play an important role in explaining the deviation of HUDGs from BTFR.