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The Red MSX Source Survey
Massive Star Formation in the Milky Way
Stuart Lumsden
University of Leeds
RMS Team:Melvin Hoare, Rene Oudmaijer, Heather Cooper, Ben Davies (Leeds) Joe Mottram (Exeter)James Urquhart (ATNF)Toby Moore (Liverpool JMU)Michael Burton (UNSW)
Massive Young Stellar Objects
Luminous (>104 L), embedded IR source.
Compact, ionised “wind” (emission lines have v~100 km/s) – radio “weak”.
Often present:
Molecular outflow/ Maser emission
Well characterised MYSOs number in the tens
Not found systematically, most nearby, may not be representative
GL2591
Gemini JHK
Evolutionary Outline
IRDCs? Hot Core MYSO UCHII
SED:
Ext. maps Sub-mm/FIR Mid-IR Mid/Near-IR
Masers:
Ice chemistry CH3OH H2O OH
Radio:
No radio Weak Radio Strong Radio
Why are MYSOs Important?
Final mass of star may be set in this phase (evidence for ongoing accretion)
Outflow/momentum transfer to natal cloud may peak/terminate at this time
Allows us to test models of massive star formation (eg collapse + disk accretion versus competitive accretion) before all the significant evidence is destroyed by the emergent OB star(s)
The Red MSX Source (RMS) SurveyMSX survey: 8, 12, 14 and 21µ m, 18″ resolution, |b|<5o
Colour-select massive from the MSX PSC and 2MASS
Delivers ~2000 candidates: http://www.ast.leeds.ac.uk/RMS • Massive YSOs + UCHII regions + PN + C stars + OH/IR stars
Multi-wavelength Ground-based Follow-up Campaign
Radio continuum (2arcsec resn, 5GHz, ATCA & VLA):
~500 detected UCHII regions (Urquhart et al. 2007, 2009) powered by O7+ stars
Mid-IR (Glimpse, ground-based, Mottram et al 2007) give morphology (MYSO ~ point source)
Contours: 6 cm
Greyscale: 8 µ m
Multi-wavelength Ground-based Follow-up Campaign
Kinematic Distances:
13CO at Mopra, JCMT, Onsala, PMO & GRS (Urquhart et al. 2007, 2008) – ambiguity within solar circle solved using HII method after sources (MYSOs + HIIs) grouped into complexes (not complete)
Near IR spectra gives final class + source properties
Luminosities
MIPSGAL 70µ m (15’ across)
SED fitting (Robitaille et al 2007)
Far-IR fluxes (MIPSGAL and Hi-GAL corrected for non-linearities) are combined with the distances to yield the luminosities (Mottram, PhD thesis 2008)
Final RMS Aims – Testing SF Models
Luminosity Function for massive YSOs =>
Massive star formation rate
IMF
Accretion rate history
Envelope dispersal history
Clustering and triggering
High spatial/spectral resolution studies as function of luminosity, age and location.
Testing Star Formation Models
Hosokawa & Omukai (2008): B0- have
“puffed up” atmospheres, cooler, less UV
McKee & Tan (2003): Accretion rate history with time
Testing Star Formation Models
Davies et al 2009
Simulated Star Formation:
Star Formation follows gas distribution Galaxy
Assume SF rate 3M yr-1
Accretion rate history from McKee & Tan (2003)
When on MS, compute radio emission (HII region)
Let it evolve for 1 Myr
Then select using RMS criteria (distance, IR, L, radio flux)
Testing Star Formation Models
Davies et al 2009
Distribution with Galactocentric radius
Early results: galactic distribution and numbers well
reproduced already (Davies et al. 2009)
Testing Star Formation Models
And Galactic longitude and latitude
As is luminosity distribution (Davies et al 2009)
Luminosity Distribution
Luminosity distribution also correct shape – but observed data shows that objects not clearly defined as just HII or YSO helps fill the gap where there are no massive YSOs
Observed data of ~50% of sample with firm distances
MYSO (CO bandhead emission) in HII region – star has Teff~36000K
UCHII region
HII/YSO example
Summary
RMS survey has delivered ~500 MYSOs and a similar number of compact HII regions across the galaxy.
Allows systematic global studies of trends for the first time – MYSOs mostly appear as lower luminosity than UCHII regions, but some evidence for rare, young O8+ MYSOs as well.
Source Identification
Sample definition complete. From distances: sample is Galaxy wide.
Mottram, PhD thesis 2008
Galactic Distribution
Large scale clustering of MYSOs, UCHIIs and CO cores to establish group membership (GRS & SCUBA2)
Spatial correlation analysis to test global star formation models
Emission Line Properties
◘ Carr (1990) observations of TTauri stars
* Ishii et al (2001) observation of HAeBes
X RMS, Clarke PhD thesis 2007