Multiwavelength study of the infrared dust bubble S51
  We investigate the environment of the infrared dust bubble S51 and search for evidence of triggered star formation in its surroundings. We performed a multiwavelength study of the region around S51 with data taken from large-scale surveys: 2MASS, GLIMPSE, MIPSGAL, IRAS, and MALT90. We analyzed the spectral profile and the distribution of the molecular gas (13CO, C18O, HCN, HNC, HCO+, C2H, N2H+, and HC3N), and dust in the environment of S51. We used mid-infrared emission three-color image to explore the physical environment and GLIMPSE color-color diagram [5.8]-[8.0] versus [3.6]-[4.5] to search for young stellar objects and identify the ionizing star candidates. From a comparison of the morphology of the molecular gas and the Spitzer 8.0 \mu m emission, we conclude that the dust bubble is interacting with CO at a kinematic distance of 3.4 kpc. The bubble S51 structure, carried with shell and front side, is exhibited with 13CO and C18O emission. Both outflow and inflow may exist in sources in the shell of bubble S51. We discover a small bubble G332.646-0.606 (R_in = 26", r_in = 15", R_out = 35" and r_out = 25") located at the northwest border of S51. A water maser, a methanol maser and IRAS 16158-5055 are located at the junction of the two bubbles. Several young stellar objects are distributed along an arc-shaped structure near the S51 shell. They may represent a second generation of stars whose formation was triggered by the bubble expanding into the molecular gas. 
Chuan Peng Zhang, Jun Jie Wang
astro-ph.GA astro-ph.SR physics.space-ph