Magnetic fields in low-density ionized gas Insights into star-formation on galaxy scales Lisa...
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Transcript of Magnetic fields in low-density ionized gas Insights into star-formation on galaxy scales Lisa...
Magnetic fields in low-density ionized gasInsights into star-formation on galaxy scales
Lisa Harvey-Smith Collaborators: Bryan
CSIRO SKA Project Scientist Gaensler, Greg Madsen
CSIRO Astronomy & Space Science
16th September 2010
The big picture
CSIRO. Lisa Harvey-Smith
CSIRO. Lisa Harvey-Smith
• Motivation:
• To assist modelling of star-formation on galactic scales
• “What is state of pressure-gravity balance in the Galaxy disk?”
• To understand how diffuse matter forms into molecular clouds and ultimately, into stars.
• “Do magnetic fields couple to matter in the diffuse ISM?”
• Method:
• Measure magnetic fields in low-density ionized gas in our Galaxy
• Use large HII regions, as they provide a ‘lit up’ B field (Faraday)
• Measure relationship between B and ρ at low gas densities
• Calculate thermal, magnetic, turbulent and total pressures in diffuse component of gas disk
• Compare results to models of self-regulated star-formation feedback in the Galactic disk.
The project
Results: Mean B and ρ in evolved HII regions
CSIRO. Lisa Harvey-Smith
Results
CSIRO. Lisa Harvey-Smith
Slope of B vs ρ in low density gas is consistent with zero.
Suggests that low-density ionized gas ‘ignores’ magnetic field.
There is also thermal – magnetic pressure balance in the HII regions.
We calculated thermal, magnetic & turbulent (from H-alpha line widths) components of the total pressure.
Conclusions
CSIRO. Lisa Harvey-Smith
• Thermal plasma beta = 1 (equipartition of magnetic & thermal pressures)
• HII regions not thermally expanding – although ionization fronts may be.
• In the warm ionized medium, material accumulates along field lines.
• Total/thermal pressure ratio used by Ostriker (2010) too high by factor of 2.
• Important to expand this work – measure z dependence of pressure.
• Experimental refinements will lead to a large reduction in uncertainties.
• ASKAP & SKA will enable measurement of B in compact/uc HII regions.
Contact UsPhone: 1300 363 400 or +61 3 9545 2176
Email: [email protected] Web: www.csiro.au
Thank you
CSIRO Astronomy & Space ScienceLisa Harvey-SmithCSIRO SKA Project Scientist
CSIRO. Lisa Harvey-Smith