Massive Young Stars in the Galaxy

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Massive Young Stars in the Galaxy

• Melvin Hoare
• University of Leeds
• UK

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Outline

• Introduction
• Massive YSOs
• High resolution observations
• The RMS Survey
• Galaxy-wide survey for massive YSOs
• Next generation galactic plane surveys
• UKIDSS GPS, SCUBA2, CORNISH
• Conclusions

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Massive Star Formation

• What determines the upper IMF?
• The physics of infall
• Turbulence?
• Magnetic fields?
• Dynamics?
• The physics of outflow
• Radiation pressure on dust?
• Radiation pressure on gas?
• MHD driven flows?

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Massive Young Stellar Objects

• Luminous (gt104 L), embedded IR source
• Bipolar molecular outflow
• Often has associated maser emission
• Compact, ionised wind (v100 km s-1)

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Evolutionary Outline

• Hot Core à YSO à UCHII à OB Star
• SED
• Sub-mm à Mid-IR à Near-IR à Visual
• Masers
• CH3OH à H2O à OH
• Radio
• No radio à Weak Radio à Strong Radio

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High Resolution Observations
S140 IRS 1
OVRO 2.7mm 2 " CO 4 "
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VLA 5 GHz (1.4 GHz)
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VLA 8 GHz Tofani et al. (1995)
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MERLIN 5 GHz 0.1" 2mm speckle 0.2"
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• Monopolar reflection nebula in a massive YSO
• Scattered light in blueshifted outflow lobe
• Polarimetry confirms scattered nature of
  extended emission

S140 IRS 1
Schertl et al (2000)
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Radio Proper Motions
5 year baseline
1 month baseline
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Mid-IR Diffraction-Limited Imaging
- Subaru 24.5mm, 0.6 resolution - Fujiyoshi,
Hoare, Moore
S140 IRS 1, 2 3
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24.5mm images
GL 989
Standard Star
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Azimuthally-averaged profiles
24.5mm
10.5mm
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Resolution of warm dust emission

• Models with r-2, r-1.5, r-1, r-0.5 density
  distribution
• Observations support steep density gradient

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Mm Interferomety

• Resolution of the cool dust continuum emission
  from the envelope
• ATCA mm interferometer
• 5 x 22m dishes and 128 MHz bandwidth
• Hoare, Urquhart, Gibb, in prep

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MYSO Samples

• Well characterised MYSOs number in the tens
• Not systematically found and mostly nearby
• May not be representative
• Need well-selected sample that number in the
  hundreds
• Can then study properties in a statistically
  robust way

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Surveys for MYSOs

• Too obscured in near-IR
• Radio continuum too weak
• No single maser transition always present
• Molecular cores do not necessarily contain YSOs
• Need to use IR where bulk of energy emerges
• IRAS-based searches suffer from confusion

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The MSX Galactic Plane Survey

• 8, 12, 14 and 21mm, 18² resolution, blt5o

W75 N Region
IRAS 12mm
MSX 8mm
MSX 21mm
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The Red MSX Source (RMS) Survey

• Colour-select massive YSO candidates from the MSX
  Point Source Catalogue and 2MASS near-IR survey
• Delivers 2000 candidates
• Many other object types with similar near- and
  mid-IR colours

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Massive YSOs
C stars
UCHII regions
OH/IR stars
PN
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Multi-wavelength Ground-based Follow-up Campaign

• Identify and eliminate confusing sources
• Begin characterisation of the massive YSOs
• RMS Team
• Stuart Lumsden, Rene Oudmaijer, James Urquhart,
  Ant Busfield, Tamara King, Andrew Clarke (Leeds,
  UK)
• Toby Moore, James Allsopp (Liverpool JMU, UK)
• Cormac Purcell, Michael Burton (UNSW, Australia)
• Zhibo Jiang, Wang Min (PMO, China)

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Radio Continuum

• 5 GHz, 1² resolution at VLA ATCA
• 1700 objects observed so far

Compact H II Region
Massive YSO candidate
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Kinematic Distances

• 13CO at Mopra, Onsala, JCMT, PMO GRS
• 1700 targets observed

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Galactic Distribution
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Resolving Distance Ambiguities with H I
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Mid-IR

• 10mm, 0.8² resolution at UKIRT and ESO 3.6m, 350
  objects observed GLIMPSE

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Near-IR

• K-band imaging at UKIRT ANU 2.3m 2MASS
• 400 targets observed
• HK band spectroscopy at UKIRT
• 120 targets observed

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Next Generation Plane Surveys

• Deeper and higher spatial resolution
• Complete wavelength coverage
• Common areas
• Matched sensitivities and resolutions
• The Spitzer 4-8mm GLIMPSE legacy survey is the
  starting point (10oltllt65o, blt1o)

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Proposed VLA Survey

• CORNISH Project (Hoare, Diamond, Churchwell,
  Kurtz, )
• CO-ordinated Radio N Infrared Survey for
  High-mass star formation
• 5 GHz, 1² resolution B configuration VLA survey
  of the northern GLIMPSE region
• 9000 pointings of 2 minutes each requiring 400
  hours in total
• 2 mJy 50 completeness limit

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CORNISH Science

• Unbiased census of UCHII regions
• Triggering and clustering of massive star
  formation
• Identification of radio loud/quiet objects found
  in GLIMPSE
• UCHII regions/Massive YSOs
• PN/Proto-PN
• Be stars, WR stars, active binaries, X-ray
  sources etc.
• Legacy science

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H II region MYSO
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Conclusions

• High resolution observations are beginning to
  resolve the envelope and winds
• The RMS survey will deliver 1000 massive YSOs
  over the whole galaxy
• GLIMPSE, in combination with other surveys, will
  deliver very large numbers of intermediate mass
  YSOs right across the inner galaxy.

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• Large well-selected samples for future high
  resolution studies e.g. 8m, ALMA, SKA
• The combination of GLIMPSE and UKIDSS GPS will be
  particularly powerful for YSO, evolved star and
  stellar population studies
• Future SCUBA2, HERSCHEL and CORNISH surveys will
  be excellent tools for systematic massive star
  formation studies