In recent years, our theoretical understanding of what establishes the onset of galaxy formation on small galaxy scales within the Lambda-Cold Dark Matter (LCDM) model has become increasingly mature, to the point that the halo occupation fraction, namely, the fraction of halos that host a luminous galaxy in their centre is now well understood in terms of the interplay between dark matter halo mass assembly histories and the existence of a redshift-dependent “critical mass” for galaxy formation. This enables predictions regarding the count of faint nearby dwarfs and some of their properties, including their gas fraction, neutral hydrogen content, and star formation histories, among others.
Interestingly, these models also predict the existence of a significant population of starless halos with masses just under the critical mass. These starless halos elude the complexities associated with star formation and the subsequent supernova feedback and contain enough neutral hydrogen to produce a significant emission in 21 cm. In addition, they display interesting properties that might help to distinguish them from luminous galaxies.
In this talk, I will discuss these systems and the theoretical background supporting their existence. I will focus on a recent detection of extended 21 cm emission consistent with one of these starless dark matter halos carried out with the Five-hundred Aperture Radio Telescope (FAST) and the Very Large Array (VLA). I will also discuss how these observations can be used to constrain the nature of dark matter, the LCDM, and galaxy formation models at the smallest scales.
I will end my talk by discussing current uncertainties and future theoretical and observational directions that may lead to further improvements.