The History and Rate of Star Formation within the G305 Complex
Abstract
Within this thesis, we present an extended multiwavelength analysis of the rich massive Galactic
star-forming complex G305. We have focused our attention on studying the both the embedded
massive star-forming population within G305, while also identifying the intermediate-, to lowmass
content of the region also. Though massive stars play an important role in the shaping and
evolution of their host galaxies, the physics of their formation still remains unclear. We have
therefore set out to studying the nature of star formation within this complex, and also identify
the impact that such a population has on the evolution of G305.
We firstly present a Herschel far-infrared study towards G305, utilising PACS 70, 160 μm and
SPIRE 250, 350, and 500 μm observations from the Hi-GAL survey of the Galactic plane. The
focus of this study is to identify the embedded massive star-forming population within G305, by
combining far-infrared data with radio continuum, H2O maser, methanolmaser,MIPS, and Red
MSX Source survey data available from previous studies. From this sample we identify some
16 candidate associations are identified as embedded massive star-forming regions, and derive
a two-selection colour criterion from this sample of log(F70/F500)! 1 and log(F160/F350)!
1.6 to identify an additional 31 embedded massive star candidates with no associated starformation
tracers. Using this result, we are able to derive a star formation rate (SFR) of 0.01 -
0.02 M! yr−1. Comparing this resolved star formation rate, to extragalactic star formation
rate tracers (based on the Kennicutt-Schmidt relation), we find the star formation activity is
underestimated by a factor of !2 in comparison to the SFR derived from the YSO population.
By next combining data available from 2MASS and VVV, Spitzer GLIMPSE and MIPSGAL,
MSX, and Herschel Hi-GAL, we are able to identify the low-, to intermediate-mass YSOs present
within the complex. Employing a series of stringent colour selection criteria and fitting reddened
stellar atmosphere models, we are able remove a significant amount of contaminating sources
from our sample, leaving us with a highly reliable sample of some 599 candidate YSOs. From this
sample, we derive a present-day SFR of 0.005±0.001M! yr−1, and find the YSOmass function
(YMF) of G305 to be significantly steeper than the standard Salpeter-Kroupa IMF. We find
evidence of mass segregation towards G305, with a significant variation of the YMF both with
the active star-forming region, and the outer region. The spatial distribution, and age gradient,
of our 601 candidate YSOs also seem to rule out the scenario of propagating star formation
within G305, with a more likely scenario of punctuated star formation over the lifetime of the
complex.