Surveying the Milky Way with the Australia Telescope

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Surveying the Milky Way with the Australia
Telescope

• Naomi McClure-Griffiths
• ATNF
• ATNF Steering Committee
• 15 April 2002

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Southern Galactic Plane Survey

• Project Team
• Naomi McClure-Griffiths
• ATNF
• John Dickey
• University of Minnesota
• Bryan Gaensler
• Harvard University
• Anne Green
• University of Sydney

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Outline

• Introduction
• What is the Southern Galactic Plane Survey?
• Why do we need it?
• Science
• What are we learning from the SGPS about the very
  big and very small?
• HI shells, supershells and chimneys
• HI Self-Absorption
• Conclusions and Future Work

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What is the Southern Galactic Plane Survey?

• 21 cm continuum and HI spectral line survey of
  the 4th quadrant of the Galactic Plane
• The SGPS is comprised of two sub-surveys
• The Parkes survey
• The Australia Telescope Compact Array (ATCA)
  survey
• Specifications
• Coverage 253º? l ? 358º, -1.5º? b ? 1.5º
• ATCA mosaics and Parkes multibeam data (inner 7
  beams)
• 2 arcmin resolution, 10 times previous Parkes
  surveys
• Spectral resolution of 0.8 km s-1
• Full Stokes parameters in the ATCA continuum data
• Parkes coverage to b 10º
• rms noise of 400 mJy Bm-1 in the continuum, 1.6 K
  Tb in the line

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CGPS
VGPS
SGPS
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Why do we need the Southern Galactic Plane Survey?

• To provide an HI atlas of the Galaxy that is
  comparable in resolution and sensitivity to CO,
  far-IR, and H? surveys
• There are so many questions to be answered about
  the Galaxy
• How does the HI distribute itself?
• What are the dynamics of the HI throughout the
  Galaxy?
• Where are the spiral arms?
• What are the variations in scale height?
• What are the temperatures of the warm and cold
  HI?
• What is the magnetic field structure of the
  Galaxy?
• What does the magnetoionic medium look like?
• And my personal favorites
• What can we learn about the interaction of
  massive stars and the ISM from HI shells,
  supershells, and chimneys?
• What impact do these structures have on the ISM
  and Galactic structure?

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Why do the SGPS now?

• H I studies of the Galaxy had reached a plateau
  by the 70s
• Limited by resolution with single dishes ( ¼- ½
  deg)
• Mapping large areas with interferometers
  inefficient
• Interferometers arent sensitive to large angular
  scales
• Recent advantages have made this survey possible
• Mosaicing with an interferometer
• Process of combining many pointings to create an
  image of an area larger than the primary beam of
  the interferometer
• Single dish focal plane arrays (i.e. Parkes
  Multibeam)
• Single dish and interferometer data combination
  techniques
• This one is particularly important, as both the
  ATCA survey and the Parkes survey are really only
  useful together

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Parkes HI Cube
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fcal x
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ATCA only
Slices across SGPS Test Region continuum images
ATCA Parkes
Parkes only
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Polarization Image
HII Region
Vela SNR
Linearly polarized intensity (Q² U²)½
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Combined HI Cube
ATCA
Combined
Parkes
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ISM and Star Formation Cycle
SN Explosions
Hot Gas
Stellar winds
shells
H I Emission
chimneys
Diffuse clouds
nucleosynthesis
H I Absorption
Molecular emission lines masers
Molecular clouds
Star Formation
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Galactic Supershells GSH 2770036

• Large void in the HI at l277º, b0º, v36 km/s
• Distance 6.5 kpc
• Physical scale
• Radius 305 pc
• Height gt 1.1 kpc
• At the edge of the Sgr-Car arm
• Chimney out both sides of the plane
• Formed by 300 massive stars

Galactic latitude
Galactic longitude
McClure-Griffiths et al. 2000
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Galactic Chimney
McClure-Griffiths et al. in prep.
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GSH 2560063
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Galactic Shells

• HI shells can be used as fossils to trace star
  formation history of the Galaxy
• Cataloged 19 new HI shells
• How do shells vary with Galactic radius?
• Largest shells in the outer regions of the Galaxy
• How are shells distributed with respect to spiral
  structure?
• Large shells seem to lie between the spiral arms

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HI Self-Absorption (HISA)
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HI Self-Absorption (HISA)

• HISA seen in new high-resolution surveys of the
  Galaxy (Gibson et al. 2000)
• Deep features with narrow velocity widths ( 1-3
  km s-1) and small angular size
• Derive naïve Tspin30K
• Emission-absorption observations over-estimate
  Tspin, since warm and cold gas are mixed on small
  scales, so Tcool may be only 20 K
• Appear to trace the spiral shocks in the inner
  Galaxy

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A wider view of Cold HI and Molecular Clouds
From the CGPS Gibson et al. (2000)
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Conclusions

• The SGPS is
• An HI and 21 cm continuum survey of 253º? l ?
  358º, -1.5º? b ? 1.5º
• Parkes expanded to -10º? b ? 10º
• We expect to
• Release u-v data immediately
• Full data release by the end of the year
• Here I have presented some of the work we are
  doing with the SGPS, including
• The very large HI Shells
• The very small HISA
• What can we learn from more studies?

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The Future of Galactic Surveys SKA

• The current IGPS goal is to survey the entire
  Galaxy to 1, 1, 1 (1 km s-1 spectral
  resolution, 1 K brightness temperature
  sensitivity, 1 arcmin angular resolution)
• With the SKA, we could redo the entire SGPS
  (Parkes coverage) to a resolution of 6 arcsec to
  1 K in 2200 hours
• The result would be an atlas of the Milky Way
  disk to a resolution of 0.1 pc!