The RMS Survey: Critical Tests of Accretion Models for the Formation of
  Massive Stars
  There is currently no accepted theoretical framework for the formation of the
most massive stars, and the manner in which protostars continue to accrete and
grow in mass beyond \sim10Msun is still a controversial topic. In this study we
use several prescriptions of stellar accretion and a description of the
Galactic gas distribution to simulate the luminosities and spatial distribution
of massive protostellar population of the Galaxy. We then compare the
observables of each simulation to the results of the Red MSX Source (RMS)
survey, a recently compiled database of massive young stellar objects. We find
that the observations are best matched by accretion rates which increase as the
protostar grows in mass, such as those predicted by the turbulent core and
competitive accretion (i.e. Bondi-Hoyle) models. These 'accelerating accretion'
models provide very good qualitative and quantitative fits to the data, though
we are unable to distinguish between these two models on our simulations alone.
We rule out models with accretion rates which are constant with time, and those
which are initially very high and which fall away with time, as these produce
results which are quantitatively and/or qualitatively incompatible with the
observations. To simultaneously match the low- and high-luminosity YSO
distribution we require the inclusion of a 'swollen-star' pre-main-sequence
phase, the length of which is well-described by the Kelvin-Helmholz timescale.
Our results suggest that the lifetime of the YSO phase is \sim 10^5yrs, whereas
the compact Hii-region phase lasts between \sim 2 - 4 \times 10^5yrs depending
on the final mass of the star. Finally, the absolute numbers of YSOs are best
matched by a globally averaged star-formation rate for the Galaxy of
1.5-2Msun/yr.
