The molecular cloud core M17-North: ISO spectroscopy and IR/mm continuum mapping

Abstract

We present the first complete infrared spectrum of a molecular cloud core covering the wavelength region from 2.4 up to 200mu m together with a map at 1.3mm wavelength and near-infrared (NIR) images. The core is located in the northern part of M17 and shows strong evidence for on-going star formation. These data are the first step towards a complete characterization of M17-North. The spectrum has been obtained with the Infrared Space Observatory (ISO) using the short- and long-wavelength spectrometers (SWS/LWS) with a resolution from 150 to 300. The spectrum of the core displays the unidentified infrared bands (UIBs). The continuum is rising rapidly for wavelengths larger than 15mu m which is typical for objects with stronger UV radiation fields. This continuum is probably produced by the emission from very small grains (VSGs) heated transiently. Many low-excitation fine structure lines were detected which are typical for the emission from an H Ii region. They are produced by an electron gas with a density and temperature of about 100cm(-3) and 5000K, respectively. The mapping of the continuum radiation at 1.3mm revealed the presence of a compact cloud core, whereas NIR imaging led to the detection of embedded IR objects. The observed spectral energy distribution (SED) is used to model the cloud core emission with radiative transfer (RT) calculations including the emission from VSGs. This calculation shows that the cloud core is mainly heated by an outer radiation field but needs an additional inner heating source with a luminosity of about 8000L_⊙ to explain the measurements. Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) with the participation of ISAS and NASA