  A multi-wavelength analysis of the large Galactic infrared bubble N 24 is has
been presented in this paper in order to investigate the molecular and star
formation environment around expanding HII regions. Using archival data from
Herschel and ATLASGAL, the distribution and physical properties of the dust
over the entire bubble are studied. Twenty three dense clumps are identified
using the Clumpfind2d algorithm with sizes and masses in the range 0.65-1.73 pc
and 600-16300 Msun, respectively. To analyse the molecular environment in N 24,
observations of NH3 (1,1) and (2,2) were carried out using the Nanshan 26m
radio telescope. Analysis of the kinetic temperature and gravitational
stability of these clumps suggests gravitational collapse in several of them.
The mass-size distributions of the clumps and the presence of massive young
protostars indicate that the shell of N 24 is a region of ongoing massive star
formation. The compatibility of the dynamical and fragmentation time-scales and
the overabundance of YSOs and clumps on the rim suggest that the collect and
collapse mechanism is in play at the boundary of the bubble, but the existence
of the IRDC at the edge of bubble indicates that radiation-driven implosion
mechanism may also have played a role there.
