  Cold interstellar gas systems have been used to constrain dark matter (DM)
models by the condition that the heating rate from DM must be lower than the
astrophysical cooling rate of the gas. Following the methodology of Wadekar and
Farrar (2021), we use the interstellar medium of a gas-rich dwarf galaxy, Leo
T, and a Milky Way-environment gas cloud, G33.4-8.0 to constrain DM. Leo T is a
particularly strong system as its gas can have the lowest cooling rate among
all the objects in the late Universe (owing to the low volume density and
metallicity of the gas). Milky Way clouds, in some cases, provide complementary
limits as the DM-gas relative velocity in them is much larger than that in Leo
T. We derive constraints on the following scenarios in which DM can heat the
gas: $(i)$ interaction of axions with hydrogen atoms or free electrons in the
gas, $(ii)$ deceleration of relic magnetically charged DM in gas plasma,
$(iii)$ dynamical friction from compact DM, $(iv)$ hard sphere scattering of
composite DM with gas. Our limits are complementary to DM direct detection
searches. Detection of more gas-rich low-mass dwarfs like Leo T from upcoming
21cm and optical surveys can improve our bounds.
