Characterizing star formation activity in infrared dark cloud MSXDC G048.65-00.29

Context. Infrared dark clouds (IRDCs), condensed regions of the ISM with high column densities, low temperatures and high masses, are suspected sites of star formation. Thousands of IRDCs have already been identified. To date, it has not been resolved whether IRDCs always show star formation activity and, if so, if massive star formation (greater than or similar to 8 M(circle dot)) is the rule or the exception in IRDCs.Aims. Previous analysis of sub-millimeter cores in the cloud MSXDC G048.65-00.29 (G48.65) indicates embedded star formation activity. To characterize this activity in detail, mid-infrared photometry (3-30 mu m) has been obtained with the Spitzer Space Telescope. This paper analyzes the point sources seen in the 24 mu m band, combined with counterparts or upper limits at shorter and longer wavelengths.Methods. Data points in wavelength bands ranging from 1 mu m up to 850 mu m (Spitzer IRAC, MIPS 24 and 70 mu m, archival 2MASS data and sub-millimeter counterparts) are used to compare each 24 mu m source to a set of Spectral Energy Distributions of Young Stellar Object (YSO) models. By assessing the models that fit the data, an attempt is made to identify YSOs as such and determine their evolutionary stages and stellar masses.Results. A total of 17 sources are investigated, 13 of which are classified as YSOs, primarily-but not exclusively-in an early embedded phase of star formation. The modeled masses of the central stellar objects range from sub-solar to greater than or similar to 8 M(circle dot). Every YSO is at less than 1 pc projected distance from its nearest YSO neighbor.Conclusions. IRDC G48.65 is a region of active star formation. We find YSOs in various evolutionary phases, indicating that the star formation in this cloud is not an instantaneous process. The inferred masses of the central objects suggest that this IRDC hosts only low to intermediate mass YSOs and none with masses exceeding greater than or similar to 8 M(circle dot).