Mixing Layer Theory and a Numerical Search for High Ions

1
Mixing Layer Theory and a Numerical Search for
High Ions

• Presented by Sam Leitner
• (Wesleyan University)
• Advisor Alex Lazarian
• Group Jungyeon Cho
• Alejandro Esquivel

2
ISM Variety Pack
3
ISM Variety Pack
4
ISM Variety Pack
Hot
Transition Temperature?
Cold
5
Mixing Layer

• Hot gas dissipates energy through an interface
  layer into a colder ISM phase.
• Colder gas absorbs some energy and some is
  radiated away.

6
Numeric MHD

• Pixilated physics
• Adiabatic
• Reflection prevents energy loss in x-y.
• Periodic boundary conditions in z allow flow to
  evolve to steady state.

z
y
x
7
Improved Mixing Layer Model

• Dynamically important magnetic fields
• Realistic cooling curve
• Capable of tracing heavy elements and
  non-equilibrium ionization/cooling levels.
• Turbulent interface
• Three dimensional modeling
• Capture features of magnetic field line mixing.
• Accounts for all degrees of turbulent mixing.
• High Resolution
• More space for evolution more accurate dynamics.

8
Magnetic Fields Plasma Instabilities
Density no B-field

• ISM Ions frozen to field lines

• Magnetic tension inhibits motion __ to B.
• Instabilities are altered.
• ?Eddies are elongated to B.

Density w/ B-Field
B
9
Radiative Cooling
Real Cooling
No Cooling

• Peak energy loss at 105 K
• Intermediate temperatures dissipate quickly
• PrT

Cooling Rate 10
10
Transition Temp High Ions

• Observations find an unpredicted abundance of
  high ion absorption.
• O VI, C IV, N V
• Large transition temperature zones T(1 - 3)x105
  K
• ? Efficient mixing layers

O VI
11
Efficient Turbulent Interface

• Steady state of mixing is a fully matured
  Kelvin-Helmholtz instability (white capping)
  turbulence
• Turbulence is ubiquitous
• Energy cascades from larger to smaller scales.
• Generates fractal geometry ?mixing at many scales
  over large surface area

Cooling, 3D, Turbulent Mixing Layer
12
Still To Be Done

• Implement non-equilibrium cooling code.
• Generate fake spectral data for a range of
  parameters.
• Compare to actual observations.

13
Possible Implications

• Significant step towards an
  accurate picture of midrange temperatures in the
  ISM.
• May explain ISM spectral data
  and clarify observations of other objects

14
Main References

• Benjamin, R.A., Benson, B.A. Cox, D.P., 2001,
  ApJ, 554, L225
• Cho, J., Lazarian, A., Honein, A., Knaepen, B.,
  Kassinos, S. Moin, P. 2003, ApJ 189, L77
• Savage, B.D., Sembach, K.R., Wakker, B.P.,
  Richter, P., Meade, M., Jenkins, E.B., Shull,
  J.M., Moos, H.W., Sonneborn, G., 2003, ApJS,
  146, 125
• Slavin, J.D., Shull, M. Begelman, M.C., 1993,
  ApJ, 407, 83

15
Acknowledgements

• Many Thanks To
• Alex Lazarian
• Jungyeon Cho
• Alejandro Esquivel
• Bob Benjamin
• Huirong Yan
• NSF

16
FIN
17
Local ISM

• May2003Instead, said astronomer Barry Welsh of UC
  Berkeley's Space Sciences Laboratory, the region
  around the sun is an irregular cavity of
  low-density gas that has tunnels branching off
  through the surrounding dense gas wall. Welsh and
  his French colleagues suspect that the
  interconnecting cavities and tunnels, analogous
  to the holes in a sponge, were created by
  supernovas or very strong stellar winds that
  swept out large regions and, when they
  encountered one another, merged into passageways.
  
• "When we started mapping gas in the galaxy, we
  found a deficit of neutral gas within about 500
  light years, suggesting that we are in a
  bubble-shaped cavity perhaps filled with hot,
  ionized gas," Welsh said. "But the Local Bubble
  is shaped more like a tube and should be called
  the Local Chimney.
• http//www.berkeley.edu/news/media/releases/2003/0
  5/29_space.shtml
• While the interstellar medium as a whole has an
  average density of about 0.5 atom per cubic
  centimeter, the interior of the Local Bubble has
  a density of 0.05 - 0.07 atoms/cc.
• http//spacsun.rice.edu/twg/pc120.html

18
Other ISM

• http//www.ras.ucalgary.ca/CGPS/press/aas00/pr/pr_
  14012000.html
• http//www.ras.ucalgary.ca/CGPS/pilot/
• "It probably was about 300 very massive stars
  that exploded over a span of a million years,"
  said McClure-Griffiths.
• "Or it could be something even more
  powerful--maybe a gamma-ray burst,"
• http//www.astro.umn.edu/naomi/sgps/shell.html