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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.