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.

The ISO Long Wavelength Spectrometer line spectrum of VY Canis Majoris and other oxygen-rich evolved stars

“…Several rotationinversion transitions at 1 mm have previously been detected in giant molecular clouds (Wootten et al 1991;Phillips et al 1992) and the lines near 300 GHz mapped toward Sgr B2 (van der Tak et al 2006). Several of the FIR transitions have also been observed in absorption toward Sgr B2 with ISO (Goicoechea & Cernicharo 2001;Polehampton et al 2007). …”

Herschel/PACS spectroscopy of NGC 4418 and Arp 220: H2O, H218O, OH,18OH, O I, HCN, and NH3

“…The rotation-inversion transitions lie at far-IR wavelengths, and many of them have been detected with ISO toward Sgr B2 (Ceccarelli et al 2002;Polehampton et al 2007) indicating a hot, low dense molecular layer interpreted in terms of shock conditions (Ceccarelli et al 2002). Detections of far-IR NH 3 lines in extragalactic sources were presented, together with a preliminary analysis, by G-A04 in Arp 220.…”

Nitrogen hydrides in interstellar gas

“…Interstellar NH 2 was first observed by van Dishoeck et al (1993) in absorption towards Sgr B2 in three fine-structure components of the para-NH 2 1 1,0 −1 0,1 transition with partially resolved hyperfine structure at frequencies 461 to 469 GHz. Further absorption lines of both ortho and para forms of NH 2 and NH were observed through use of the long-wavelength spectrometer aboard ISO (Cernicharo et al 2000;Goicoechea et al 2004;Polehampton et al 2007). The ISO observations were unable to resolve the hyperfine structure of either molecule.…”