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, Snežana Stanimirović, Carl Heiles and Patrick Hennebelle NRAO, Univer Wisconsin Madison, Univer Calif. Berkeley and Observatoire de Paris 3 December 2009 Australia Telescope National Facility

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 Recent VLBA (plus GBT and the VLA )data on 3C138 and 3C147.

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

3C147-HI VLBA resolution 10 mas

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

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

Confirmation by Heiles and Stanimirović, 2005

Discussion of H and S Make the possible association with TSAS – small size and column densities of ~3 x to ~ 2 x 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).’

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.’

3C VLA only antennas

EVLA only 3C 286 -S p =15.9 Jy/beam

3C 286 EVLA l=57 b=81 HI Absorption HI Emission

3C 263.1– S p = 2.2 Jy/beam l=227 b=74 HI Absorption HI Emission

3C 273- Continuum Image at 21 cm Observations in CnB May 2009

3C 273 -S p =32.7 Jy/beam l=290 b=64 HI Absorption HI Emission

J S p =3.0Jy/beam l=107, b=-62 HI Absorption HI Emission

J Residual

P Sp=1.6 Jy/beam l=182, b=-36 HI Absorption HI Emission

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