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EVLA Observations of the Low Density Component of the Cold Neutral Medium and Limits on the Thermally-Unstable Warm Neut

This study explores the low density component of the cold neutral medium (CNM) and investigates the limits of the thermally-unstable warm neutral medium (WNM) through EVLA observations. The researchers aim to understand the relationship between CNM components and tiny scale atomic structure (TSAS), and determine the abundance and properties of these clouds in the interstellar medium (ISM).

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EVLA Observations of the Low Density Component of the Cold Neutral Medium and Limits on the Thermally-Unstable Warm Neut

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  1. EVLA Observations of the Low Density Component of the Cold Neutral Medium and Limits on the Thermally-Unstable Warm Neutral Medium Miller Goss, Ayesha Begum, SnežanaStanimirović, Carl Heiles and Patrick Hennebelle NRAO, Univer Wisconsin Madison, Univer Calif. Berkeley and Observatoire de Paris 3 December 2009 Australia Telescope National Facility http://www.nrao.edu/

  2. Some History of the 2 Phase ISM • Bolton at OVRO in the late 1950s. Clark, Radhakrishnan and Wilson. • Work at Parkes starting in 1967 lead by Rad. Including the 60 foot interferometer machine for HI. Lead to the OVRO work, Greisen, Lockhart and Goss in the 1970s. • Small scale structure, by Nan Dieter (Conklin) in 1976. • Recent VLBA (plus GBT and the VLA )data on 3C138 and 3C147.

  3. TSAS- Tiny Scale Atomic Structure-3C 138 VLBA resolution 20 mas

  4. 3C147-HI VLBA resolution 10 mas

  5. Detection of WNM with the WSRT by Dwarakanath et al – 3C147

  6. The pioneering work of Braun and Kanekar at the WSRT in 2004/5- Tiny HI Clouds

  7. Confirmation by Heiles and Stanimirović, 2005

  8. Discussion of H and S • Make the possible association with TSAS – small size and column densities of ~3 x 1018 to ~ 2 x 1019 cm-2 . Sizes from few AU to hundreds AU. • ‘If the low column density HI clouds and TSAS features have a common origin, then TSAS is significantly more abundant in the ISM, and with significantly lower optical depths, than what is expected theoretically if the TSAS is a simply the low size scale extension of the IS turbulence spectrum as discussed by Deshpande (2000).’

  9. Discussion of H and S contd • ‘Observationally, it is essential to quantify how common these clouds are in the ISM and whether they are related to some local events, such as stellar winds or large-scale atomic flows. We need to increase the statistical sample to establish the probability density function of the column density in the vicinity of the lower cutoff, where most of the low N(HI) clouds are found. In addition we need to more firmly determine the relationship between the CNM components found here and the TSAS.’

  10. 3C 286 2008 -VLA only antennas

  11. EVLA only 3C 286 -Sp=15.9 Jy/beam

  12. 3C 286 EVLAl=57 b=81 HI Absorption HI Emission

  13. 3C 263.1– Sp = 2.2 Jy/beam l=227 b=74 HI Absorption HI Emission

  14. 3C 273- Continuum Image at 21 cmObservations in CnB May 2009

  15. 3C 273 -Sp=32.7 Jy/beaml=290 b=64 HI Absorption HI Emission

  16. J0022+002 - Sp=3.0Jy/beaml=107, b=-62 HI Absorption HI Emission

  17. J0022+002 Residual

  18. P0347+58 -Sp=1.6 Jy/beaml=182, b=-36 HI Absorption HI Emission

  19. Conclusions: • Wait until I get the Ts fits etc at the end of the week from Madision

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