The ISO LWS high-resolution spectral survey towards Sagittarius B2

Abstract

A full spectral survey was carried out towards the giant molecular cloud complex, Sagittarius B2 (Sgr B2), using the Infrared Space Observatory (ISO) Long Wavelength Spectrometer (LWS) Fabry–Pérot mode. This provided complete wavelength coverage in the range 47–196 μm (6.38–1.53 THz) with a spectral resolution of 30–40 km s−1. This is a unique data set covering wavelengths inaccessible from the ground. It is an extremely important region of the spectrum as it contains both the peak of the thermal emission from dust, and crucial spectral lines of key atomic (O i, C ii, O iii, N ii and N iii) and molecular species (NH3, NH2, NH, H2O, OH, H3O+, CH, CH2, C3, HF and H2D+). In total, 95 spectral lines have been identified and 11 features with absorption depth greater than 3σ remain unassigned. Most of the molecular lines are seen in absorption against the strong continuum, whereas the atomic and ionic lines appear in emission (except for absorption in the O i 63 μm and C ii 158 μm lines). Sgr B2 is located close to the Galactic Centre and so many of the features also show a broad absorption profile due to material located along the line of sight. A full description of the survey data set is given with an overview of each detected species and final line lists for both assigned and unassigned features.