Infrared study of the star-forming region associated with the UC HII regions G45.07+0.13 and G45.12+0.13

Abstract

UCHII regions are an important phase in the formation and early evolution of massive stars and a key component of the interstellar medium. The main objectives of this work are to study the young stellar objects (YSOs) associated with the G45.07+0.13 (G45.07) and G45.12+0.13 (G45.12) UCHII regions, as well as the interstellar medium in which they are embedded. We determined the distribution of the hydrogen column density (N(H2)) and dust temperature (Td) in the molecular cloud using Herschel images. We used infrared photometric data to identify and classify the YSOs. We also constructed a colour-magnitude diagram and K luminosity functions (KLFs) to compare the parameters of YSOs with the results of the radiative transfer models. We found that N(H2) varies from about 3.0 to 5.5x10^(23)cm^(-2) within the G45.07 and G45.12 regions, respectively. The maximum Td value is 35K in G45.12 and 42K in G45.07. Td reaches about 18-20K at distances of 2.6 and 3.7pc from IRAS19110+1045 (G45.07) and IRAS19111+1048 (G45.12), respectively. The gas-dust mass value included in G45.12 is 3.4x10^5Msun and 1.7x10^5Msun in G45.07. The UCHII regions are connected through a cold (Td=19K) bridge. The density distribution of 518 YSOs exhibits dense clusters around both IRAS sources. The parameters of YSOs in the IRAS clusters (124 objects) and 394 non-cluster objects surrounding them show some differences. About 75% of the YSOs belonging to the IRAS clusters have an evolutionary age greater than 10^6 years. Their slope alpha of the KLF agrees well with a Salpeter-type Initial Mass Function (IMF) (gamma=1.35) for a high mass range (O-F stars, beta=2) at 1Myr. The non-cluster objects are uniformly distributed in the molecular cloud, 80% of which are located to the right of the 0.1Myr isochrone. Based on the small age spread of the stellar objects, we suggest that the clusters originate from a single triggering shock.

The paper has been accepted for publication in PASA. It includes 11 figures and 6 tables

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