The RMS survey: near-IR spectroscopy of massive young stellar objects

Near-infrared H-and K-band spectra are presented for 247 objects, selected from the Red MSX Source (RMS) survey as potential young stellar objects (YSOs). 195 (similar to 80 per cent) of the targets are YSOs, of which 131 are massive YSOs (L-BOL > 5 x 10(3) L-circle dot, M > 8 M-circle dot). This is the largest spectroscopic study of massive YSOs to date, providing a valuable resource for the study of massive star formation. In this paper, we present our exploratory analysis of the data. The YSOs observed have a wide range of embeddedness (2.7 < A(V) < 114), demonstrating that this study covers minimally obscured objects right through to very red, dusty sources. Almost all YSOs show some evidence for emission lines, though there is a wide variety of observed properties. The most commonly detected lines are Br gamma, H-2, fluorescent Fe II, CO bandhead, [Fe II] and He I 2-1 S-1-P-1, in order of frequency of occurrence. In total, similar to 40 per cent of the YSOs display either fluorescent Fe II 1.6878 mu m or CO bandhead emission (or both), indicative of a circumstellar disc; however, no correlation of the strength of these lines with bolometric luminosity was found. We also find that similar to 60 per cent of the sources exhibit [Fe II] or H-2 emission, indicating the presence of an outflow. Three quarters of all sources have Br gamma in emission. A good correlation with bolometric luminosity was observed for both the Br gamma and H-2 emission line strengths, covering 1 < L-BOL < 3.5 x 10(5) L-circle dot. This suggests that the emission mechanism for these lines is the same for low-, intermediate-and high-mass YSOs, i.e. high-mass YSOs appear to resemble scaled-up versions of low-mass YSOs.