2012A&A...537A.149D

We present a study of the molecular gas and interstellar dust distribution in the environs of the HII region NGC3503 associated with the open cluster Pis17 with the aim of investigating the spatial distribution of the molecular gas linked to the nebula and achieving a better understanding of the interaction of the nebula and Pis17 with their molecular environment. We based our study on ¹²CO(1-0) observations of a region of ∼0.6deg in size obtained with the 4-m NANTEN telescope, unpublished radio continuum data at 4800 and 8640MHz obtained with the ATCA telescope, radio continuum data at 843MHz obtained from SUMSS, and available IRAS, MSX, IRAC-GLIMPSE, and MIPSGAL images. We found a molecular cloud (Component 1) having a mean velocity of -24.7km/s, compatible with the velocity of the ionized gas, which is associated with the nebula and its surroundings. Adopting a distance of 2.9±0.4kpc, the total molecular mass yields (7.6± 2.1)x10³M_☉ and density yields 400±240cm^–3. The radio continuum data confirm the existence of an electron density gradient in NGC3503. The IR emission shows a PDR bordering the higher density regions of the nebula. The spatial distribution of the CO emission shows that the nebula coincides with a molecular clump, and the strongest CO emission peak is located close to the higher electron density region. The more negative velocities of the molecular gas (about -27 km/s), are coincident with NGC3503. Candidate young stellar objects (YSOs) were detected toward the Hiiregion, suggesting that embedded star formation may be occurring in the neighborhood of the nebula. The clear electron density gradient, along with the spatial distribution of the molecular gas and PAHs in the region indicates that NGC3503 is a blister-type Hii region that has probably undergone a champagne phase.