  In the standard cosmological model, dark matter drives the structure
formation and constructs potential wells within which galaxies may form. The
baryon fraction in dark halos can reach the universal value (15.7%) in massive
clusters and decreases rapidly as the mass of the system decreases. The
formation of dwarf galaxies is sensitive both to baryonic processes and the
properties of dark matter owing to the shallow potential wells in which they
form. In dwarf galaxies in the Local Group, dark matter dominates the mass
content even within their optical-light half-radii (r_e ~ 1 kpc). However,
recently it has been argued that not all dwarf galaxies are dominated by dark
matter. Here we report 19 dwarf galaxies that could consist mainly of baryons
up to radii well beyond r_e, at which point they are expected to be dominated
by dark matter. Of these, 14 are isolated dwarf galaxies, free from the
influence of nearby bright galaxies and high dense environments. This result
provides observational evidence that could challenge the formation theory of
low-mass galaxies within the framework of standard cosmology. Further
observations, in particular deep imaging and spatially-resolved kinematics, are
needed to constrain the baryon fraction better in such galaxies.
