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 (~80%) of the targets are YSOs, of which 131 are massive YSOs (L_BOL >
5x10^3 L_solar), M > 8M_solar. 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 Brgamma, H_2, fluorescent FeII, CO bandhead, [FeII] and HeI
2-1 2^1S-2^1P, in order of frequency of occurrence. In total, ~40% of the YSOs
display either fluorescent FeII 1.6878um 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 ~60% of the
sources exhibit [FeII] or H_2 emission, indicating the presence of an outflow.
Three quarters of all sources have Brgamma in emission. A good correlation with
bolometric luminosity was observed for both the Brgamma and H_2 emission line
strengths, covering 1 L_solar< L_BOL < 3.5x10^5 L_solar. 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.
