  Massive infrared dark clouds (IRDCs) are considered to host the earliest
stages of high-mass star formation. In particular, 70 $\mu$m dark IRDCs are the
colder and more quiescent clouds. At a scale of about 5000 au using
formaldehyde (H2CO) emission, we investigate the kinetic temperature of dense
cores in 12 IRDCs obtained from the pilot ALMA Survey of 70 $\mu$m dark
High-mass clumps in Early Stages (ASHES). Compared to 1.3 mm dust continuum and
other molecular lines, such as C18O and deuterated species, we find that H2CO
is mainly sensitive to low-velocity outflow components rather than to quiescent
gas expected in the early phases of star formation. The kinetic temperatures of
these components range from 26 to 300 K. The Mach number reaches about 15 with
an average value of about 4, suggesting that the velocity distribution of gas
traced by H2CO is significantly influenced by a supersonic non-thermal
component. In addition, we detect warm line emission from HC3N and OCS in 14
protostellar cores, which requires high excitation temperatures (Eu/k ~ 100 K).
These results show that some of the embedded cores in the ASHES fields are in
an advanced evolutionary stage, previously unexpected for 70 $\mu$m dark IRDCs.
