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