A multiwavelength study of the star forming region IRAS 18544+0112

Abstract

Aims: This work aims at investigating the molecular and infrared components in the massive young stellar object (MYSO) candidate IRAS 18544+0112. The purpose is to determine the nature and the origin of this infrared source. Methods: To analyze the molecular gas towards IRAS 18544+0112, we have carried out observations in a 90" × 90" region around l = 34.69°, b = -0.65°, using the Atacama Submillimeter Telescope Experiment (ASTE) in the 12CO J = 3-2, 13CO J = 3-2, HCO+J = 4-3 and CS J = 7-6 lines with an angular resolution of 22". The infrared emission in the area has been analyzed using 2MASS and Spitzer public data. Results: From the molecular analysis, we find self-absorbed 12CO J = 3-2 profiles, which are typical in star forming regions, but we do not find any evidence of outflow activity. Moreover, we do not detect either HCO+J = 4-3 or CS J = 7-6 in the region, which are species normally enhanced in molecular outflows and high density envelopes. The 12CO J = 3-2 emission profile suggests the presence of expanding gas in the region. The Spitzer images reveal that the infrared source has a conspicuous extended emission bright at 8 μm with an evident shell-like morphology of ~1.5 arcmin in size (~1.4 pc at the proposed distance of 3 kpc) that encircles the 24 μm emission. The non-detection of ionized gas related to IRAS 18544+0112 together with the fact that it is still embedded in a molecular clump suggest that IRAS 18544+0112 has not reached the UCHII region stage yet. Based on near infrared photometry we search for YSO candidates in the region and propose that 2MASS 18565878+0116233 is the infrared point source associated with IRAS 18544+0112. Finally, we suggest that the expansion of a larger nearby HII region, G034.8-0.7, might be related to the formation of IRAS 18544+0112.