Speaker
Description
The ΛCDM model successfully describes the hierarchical large-scale structure of the Universe, but it also predicts a much larger number of low-mass dark matter haloes than are actually observed. This tension can be explained by the fact that below a certain mass threshold, star formation is suppressed. However, these low-mass haloes should contain a significant amount of HI, which could be detectable through radio observations.
With the advent of high-sensitivity single-dish blind surveys (such as the FAST All-Sky HI Survey), several extragalactic HI sources with gas masses compatible with dwarf galaxies have been discovered, yet they do not present an optical counterpart even in the most sensitive optical surveys. These exotic objects are usually referred to as `dark galaxies'.
Using the FAST HI survey, we selected more than 3400 HI sources within 50 Mpc, the vast majority of which present a clear optical counterpart in the DESI Legacy Imaging Surveys, while 70 do not (Dark Galaxy Candidates, DGCs). Searching for extremely faint optical counterparts of these DGCs is crucial, since it allows us to place strict upper limits on their stellar mass and helps us understand why these systems exhibit extremely quenched star formation, or even no stars at all.
Taking advantage of the well-proven capability of the VST to detect extremely faint optical structures, we selected 12 promising DGCs to be observed with OMEGACAM@VST. With approximately 4-hour-long exposures in the g filter for each DGC under photometric conditions, we aim to reach a surface-brightness limit below 30 mag arcsec$^{-2}$. The VST's extremely wide field of view will also allow a detailed study of the environments in which these DGCs are located.
Both the detection and the non-detection of an optical counterpart will allow us to constrain the stellar mass or place an upper limit on it, and to link it with the HI properties. In the case of a detection, we will place these newly identified extremely faint dwarfs on the Tully–Fisher relation and compare their optical size with their HI mass.
In this talk, I will present an overview of the first five months of VST observations, the current status of the project, some preliminary results, and the next steps.