School of somethingFACULTY OF OTHER
School of Physics & AstronomyFACULTY OF MATHEMATICS & PHYSICAL SCIENCES
A Galaxy-Wide Census of MassiveStar Formation
Melvin Hoare, Ben Davies, Joe Mottram, James Urquhart,Melvin Hoare, Ben Davies, Joe Mottram, James Urquhart,
Stuart Lumsden, Rene Oudmaijer,
Joe Stead, Heather Cooper, Luke Maud
MSX survey of the plane
Outline
• Introduction
• Massive young stellar objects
• Red MSX Source Survey
• Colour selection
• Multi-wavelength campaign
• Initial Global Results
• Galactic distributions
• Population synthesis
• Conclusions
Massive Young Stellar Objects
• MYSOs are luminous(>104 L) embedded IRsources
• bipolar molecular outflow(~10 km s-1)(~10 km s-1)
• ongoing accretion
• ionised jet or wind(~100 km s-1)
• no UCHII region
W33A Davies et al. (2010)
Poster CP3
Evolutionary Context
L L
UCHIIs
Lbol
f70mm/ f24mm
Lbol
f21mm/ f8mm
IRDC
SourcesMYSOs
HerbigBe stars
The Red MSX Source Survey
• A systematic search for MYSOs throughout theGalactic Plane, i.e. |l|>10o, |b|<5o
• Colour-selected ~2000 candidates from the 20resolution 8-21mm survey of the plane by MSX
• Follow-up 1 resolution radio, MIR & NIR imaging toeliminate post-MS objects & identify UCHII regions
• CO kinematic distances + FIR fluxes luminosities
• Delivered a sample of ~500 MYSOs & ~500 UCHIIs
• see www.ast.leeds.ac.uk/RMS
Galactic Distribution
Population Synthesis Models
• Distribute in a spiral arm model(Cordes & Lazio 2002)
• SFR a n1.4 (Schmidt-Kennicutt)
• Sample from a Kroupa IMF• Sample from a Kroupa IMF
• Assume an accretion rate history
• Transition to UCHII when on ZAMSand Strömgren expansion thereafter
• Include selection criteria F21>MSXcompleteness limit (~3 Jy), f<20
• Check total Galactic SFR ~ 3 Myr -1
Davies et al. in prep
Accretion Rate History
Turbulent Core
McKee & Tan (2003)
Gravo-turbulent fragmentation
Schmeja & Klessen (2004)
MYSOs versus UCHIIs
• MYSOs are swollen byaccretion and thereforehave Teff < 30 000 K anddo not ionize H II regions
Hosokawa & Omukai (2009)
• No MYSOs above L~105
L (M~30 M) as theyrapidly contract to MS radiiand therefore haveTeff > 30 000 K
Contraction Phase
Hosokawa
tKH
Galacto-centric distribution
Galactic latitude distribution
Galactic longitude distribution
Completeness & H II Regions
Increasing Accretion Rate
tM
Turbulent Core Model
McKee & Tan (2003)
c2 =1.2 SFR=1.9 M yr-1
(also Bondi-Hoyle model)
Decreasing Accretion Rate
tteM
log
Gravo-turbulentfragmentation
Schmeja & Klessen (2004)
c2 =2.0 SFR=0.8 M yr-1
Constant Accretion Rate
M
form
fin
t
MM
c2 =2.1 SFR=0.5 M yr-1
Fixed Accretion Rate
constM
Evolution
Evolution
Lifetime
See also Mottram et al. soon
Conclusions
• The RMS survey has delivered a Galaxy-wide, well-selectedsample of 500 MYSOs and UCHII regions
• There is no MYSO phase for objects with L>105 L
• Consistent with high accretion rates resulting in swollenYSOs around 104 L
• Luminosity distribution not consistent with constant ordecreasing accretion rates with time
• Future work will include better galactic distribution, envelopedispersal prescription, RT models, colour distribution, etc.