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Metal Absorption in Conductively Evaporating Clouds

Metal Absorption in Conductively Evaporating Clouds. Orly Gnat, Caltech In Collaboration with : Amiel Sternberg, Chris McKee. High Velocity Metal Absorbers. UV observations revealed a population of local highly ionized absorbers ( Sembach et al. 1999, 2000, 2002, 2003;

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Metal Absorption in Conductively Evaporating Clouds

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  1. Metal Absorption in Conductively Evaporating Clouds Orly Gnat, Caltech In Collaboration with: Amiel Sternberg, Chris McKee

  2. High Velocity Metal Absorbers • UV observationsrevealed a population oflocal 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. Metal Absorbers as Photoionized Clouds • Hydrostatic spherical gas cloudsembedded in dark matter minihalosphotoionized by “metagalactic” fieldpressure 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. heat flow hot cloud evaporates Conductive Evaporation • Ionization time > heating time? warm

  5. Conductive Evaporation • Classic diffuse evaporation (Spitzer) • Saturated evaporation • Saturation parameter

  6. Conductive Evaporation • Energy Conservation: • Dalton & Balbus 1993: Bulk Kinetic Energy Internal Energy + PdV work Radiative Losses & Gain Inward Heat Flux

  7. DB93 Temperature Profiles Solutions

  8. The Non-Radiative Approximation • McKee & Cowie 1977:equilibrium cooling, Z=1 solarcritical saturation parameter • Under-ionized, over-cooled non-equilibrium gas: • Z=0.1 solar • Z=1 solar • Under-ionized He+ cooling!

  9. Ionization • H, He, C, N, O, Si, S • dx / dr = • Collisional ionization / rec. • Photoionizationby metagalactic field • Radiativerecombinations • Dielectronicrecombinations • Charge exchange with H & H+ • 0.1 < P/kB< 104 cm-3 K1 pc < R < 100 kpc5 x 105 < T < 107 K • Cooling using Cloudy

  10. Non-Eq Ionization • Under-Ionized,over-cooled gas

  11. Non-Equilibrium Columns?

  12. Metal Absorption Column Densities • For comparison with observations of metal ion absorbers • Focus on dwarf galaxy scale objects • 0.1 < P/kB< 50 cm-3 K • 1 < R < 7.5 kpc • T = 1-2 x 106 K • Column density versus impact parameter

  13. Example: compact, high-P cloud • x6 dex in OVI • x1 dex in CIV

  14. High OVI Columns in Evaporating Clouds?

  15. Summary • Non-Equilibrium of H, He, C, N, O, Si, S • Non-Radiative approximation: σ0>0.15 (Z=0.1) σ0>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 OVI columns (~1014 cm-2) • OVI limit of ~1013 cm-2 for evaporating clouds

  16. Fox et al. 2005 ApJ 630, 332 Turbulent Mixing Layers log ( CIV / OVI ) Conductive Interfaces Shock Ionization Cooling Flows log ( NV / OVI ) Equilibrium? • Fox et al. 2005

  17. Photoionization

  18. Absorption to Mrk509 &PKS2155-304 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 <12.33 - >13.44 S III 1190.2 Å <13.68 - <13.93 O VI 1031.9 Å 13.56 - 13.93

  19. Metal Absorbers as Photoionized Clouds • CHVC scale objects (Mvir~108Mo, P~50 cm-3 K)embedded in high-pressure Galactic Corona:ionization parameter too low. • Dwarf galaxy scale objects (Mvir~2x109Mo, P~0.1 cm-3 K):embedded in low pressure IGM:

  20. Used in • Local Cloud & Local bubble • ISM clouds • SNRs • AGN • Galaxy formation

  21. Previous Studies • 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

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