1. Einstein Fellows Symposium 10/27/2009 1 Orly Gnat, Caltech In Collaboration with : Amiel Sternberg, Chris McKee

2. Einstein Fellows Symposium 10/27/2009 2 UV observations revealed a population of local highly ionized absorbers (Sembach et al. 1999, 2000, 2002, 2003; Murphy et al. 2000; Wakker et al. 2003; Collins et al. 2004, Fox et al. 2005, 2006…) Sembach et al. 2003, ApJ, 146, 165S

3. Einstein Fellows Symposium 10/27/2009 3 Hydrostatic spherical gas clouds embedded in dark matter minihalos photoionized by “metagalactic” field pressure supported by an external hot medium Consider – dwarf galaxy scale objects lower mass starless minihalo models for CHVC (Sternberg McKee & Wolfire) - Gnat & Sternberg 2004, ApJ, 608, 229

4. Einstein Fellows Symposium 10/27/2009 4 Ionization time > heating time? hot warm heat flow cloud evaporates

5. Einstein Fellows Symposium 10/27/2009 5 Classic diffuse evaporation (Spitzer) Saturated evaporation Saturation parameter

6. Einstein Fellows Symposium 10/27/2009 6 Energy Conservation: Dalton & Balbus 1993: Bulk Kinetic Energy Internal Energy + PdV work Radiative Losses & Gain Inward Heat Flux

7. Einstein Fellows Symposium 10/27/2009 7

8. 8 McKee & Cowie 1977: equilibrium cooling, Z=1 solar critical saturation parameter Under-ionized, over-cooled non-equilibrium gas: Z=0.1 solar Z=1 solar Under-ionized He + cooling!

9. Einstein Fellows Symposium 10/27/2009 9 H, He, C, N, O, Si, S dx / dr = Collisional ionization / rec. Photoionization by metagalactic field Radiative recombinations Dielectronic recombinations Charge exchange with H & H + 0.1 < P/k B < 10 4 cm -3 K 1 pc < R < 100 kpc 5 x 10 5 < T < 10 7 K Cooling using Cloudy

10. Einstein Fellows Symposium 10/27/2009 10 Under-Ionized, over-cooled gas

11. Einstein Fellows Symposium 10/27/2009 11

12. Einstein Fellows Symposium 10/27/2009 12 For comparison with observations of metal ion absorbers Focus on dwarf galaxy scale objects 0.1 < P/k B < 50 cm -3 K 1 < R < 7.5 kpc T = 1-2 x 10 6 K Column density versus impact parameter

13. Einstein Fellows Symposium 10/27/2009 13 x6 dex in O VI x1 dex in C IV

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15. Einstein Fellows Symposium 10/27/2009 15 Non-Equilibrium of H, He, C, N, O, Si, S Non-Radiative approximation: σ 0 >0.15 (Z=0.1) σ 0 >0.4 (Z=1) Extension of photoionized models for metal-ion absorbers Conductive interfaces enhance formation of high ions Still too low to account for observed O VI columns (~10 14 cm -2 ) O VI limit of ~10 13 cm -2 for evaporating clouds

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17. Einstein Fellows Symposium 10/27/2009 17 Fox et al. 2005 Turbulent Mixing Layers Conductive Interfaces Cooling Flows Shock Ionization log ( N V / O VI ) log ( C IV / O VI ) Fox et al. 2005 ApJ 630, 332

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19. Einstein Fellows Symposium 10/27/2009 19 log column cm -2 C IV 1548.2 Å 13.5 - >14.20 N V 1238.8 Å <13.08 - <13.24 Si III 1012.5 Å 12.44 - 13.31 Si IV 1393.8 Å 13.44 S III 1190.2 Å <13.68 - <13.93 O VI 1031.9 Å 13.56 - 13.93

20. Einstein Fellows Symposium 10/27/2009 20 CHVC scale objects (M vir ~10 8 Mo, P~50 cm -3 K) embedded in high-pressure Galactic Corona: ionization parameter too low. Dwarf galaxy scale objects (M vir ~2x10 9 Mo, P~0.1 cm -3 K): embedded in low pressure IGM:

21. Einstein Fellows Symposium 10/27/2009 21 Local Cloud & Local bubble ISM clouds SNRs AGN Galaxy formation

22. Einstein Fellows Symposium 10/27/2009 22 Cowie & McKee 1977 McKee & Cowie 1977 Ballet, Arnaud & Rothenflug 1986 Boehringer & Hartquist 1987 Slavin 1989 Slavin & Cox 1992 Dalton & Balbus 1993 Shelton 1998 Smith & Cox 2001