Abstract We present a study of the Galactic bubble N4 using the 13.7 m millimeter-wave telescope, which is managed by Purple Mountain Observatory at Qinghai Station. N4 is one of the science demonstration regions where simultaneous observations of 12CO (J = 1 − 0), 13CO (J = 1 − 0) and C18O (J = 1 − 0) line emission towards N4 were carried out under the project Milky Way Imaging Scroll Painting (MWISP). We analyze the spectral profile and the distribution of the molecular gas. Morphologically, the CO emissions correlate well with Spitzer IRAC 8.0 μm emission. The channel map and velocity-position diagram show that N4 is more likely to be an inclined expanding ring rather than a spherical bubble. We calculated the physical parameters of N4 including mass, size, column density and optical depth. Some massive star candidates were discovered in the region of N4 using the (J, J−H) color-magnitude diagram. We found a candidate for the energy source driving the expansion of N4, a massive star with a mass of ~15 M⊙ and an age of ~ 1 Myr. There is the signature of infall motion in N4, which can be a good candidate for the infall area. Combining millimeter and infrared data, we suggest that triggered star formation can exist in N4.

Keywords ISM: bubbles — ISM: clouds — molecules — stars: formation

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