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Equilibrium & Non-Equilibrium Ionization in Metal Ion Absorbers

This research explores the photoionization properties of metals in minihalo clouds and investigates the relationship between high-velocity clouds (HVCs), dwarfs, and ionized absorbers. The study focuses on the equilibrium and non-equilibrium ionization processes in metal ion absorbers.

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Equilibrium & Non-Equilibrium Ionization in Metal Ion Absorbers

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  1. From HVCs to WHIM: Equilibrium & Non-Equilibrium Ionization in Metal Ion Absorbers Orly Gnat & Amiel Sternberg Tel Aviv University ISRAEL

  2. HI High-Velocity Clouds  Wakker et al. 2003 ApJS, 146, 1

  3. High-Velocity Metal Absorbers Sembach et al. 2003, ApJ, 146, 165S • High-velocity gasprobed by UV/optical metal-line absorption. (Sembach et al. 1999, 2000, 2002, 2003; Murphy et al. 2000; Wakker et al. 2003; Collins et al. 2004, …)

  4. Absorption toward Mrk 509 & PKS 2155-304 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 Collins et al. 2004 ApJ, 605, 216

  5. Key questions: • What are the photoionization properties of metals in minihalo clouds? • Are the HI CHVCs, dwarfs & ionized-absorbersrelated objects?

  6. Hot ionized Warm ionized Warm neutral Minihalo models: H+He properties • Warm = 104K • Spherical symmetry • In DM halos • External HIM Pressure • Ionizing field Sternberg, McKee & Wolfire 2002 ApJS 143, 419 • Hypothesis:CHVCs trace DM substructurein Galactic halo / Local Group (Blitz et al. 1999, Braun & Burton 1999) • Explicit minihalo Models for: • LG dwarfs (Leo A, Sag DIG) • HI CHVCs (Sternberg, McKee & Wolfire 2002) • Hydrostatic equilibrium • Radiative Transfer Dark Matter Minihalo

  7. Minihalo models – H+He Results: • Dwarf Galaxy model (gravitationally confined): • Mvir=2x109 M , Mgas=2x107 M , P/k=1 cm-3K • Best fit: typical LCDM Burkert halo • CHVC model (pressure confined): • Mvir=1x108 M , Mgas=1x106M , P/k=50 cm-3K • Multi-phased cores expected. • Implied distance: ~150 kpc. Sternberg, McKee & Wolfire 2002 ApJS 143, 419

  8. Dark matter LCDM Burkert profiles. Virial masses: 108 – 2x109 Mʘ. Gas 106 – 107 Mʘ , T=104K. P/kB: 0.01–50 cm-3K. Metallicity: 0.1-0.3 solar. Metagalactic radiation field. Metal absorbers – model parameters Moore et al. 2002

  9. Metagalactic radiation field IR optical UV EUV X-ray nJn[erg s-1 cm-2 sr-1 ] Lyman limit 0.25 keV Jn0 = 2 x 10-23 cgs n[Hz]

  10. 8.2 eV Si II Low-Ions 10.4 eV S II 11.3 eV C II 13.6 eV H II High-Ions 16.4 eV Si III 23.3 eV S III 33.5 eV Si IV 47.9 eV C IV 77.5 eV N V 113.9 eV O VI Metals: Ionization potentials

  11. Step 1: H/He gas density profile; ionization structure; Local radiation field. • Step 2: • CLOUDY ionization state (Ferland, 1998). • Integrate line-of-sight columns. r Metals photo-ionization structure radiative transfer (spherical),

  12. Dwarf-scale halos Photoionized models - Results CHVCs models – High bounding pressures (~50 cm-3K) low ionization. Not enough high ions: E.g. - CIV column: Observed - ~1x1014 cm-2 CHVC Model - 3x1011 cm-2

  13. Example: Dwarf-scale halo • High mass: Mvir = 2 x 109 Mʘ, Burkert halo. • Mgas = 2 x 107 Mʘ,Metallicity = 0.3 solar. • Low Pressure: 0.1 cm-3K. • Maximal radiation field. Nicastro et al. 2002 ApJ, 573, 157

  14. IF Warm neutral Hot ionized Warm ionized total H density neutral H Dwarf-scale halo: volume densities density [cm-3] Radius [kpc]

  15. Dwarf-scale halo: column densities C IV : model: 1.5 x 1014 cm-2 observed: (0.3 – 2) x 1014 cm-2 O VI : model: 1 x 1013 cm-2 observed: (4 - 8) x 1013 cm-2 Column density [cm-2] Impact parameter [kpc]

  16. Dwarf Model versus observations: Nmodel / Nobserved Impact parameter [kpc]

  17. C IV : 1 x 1014 cm-2 observed: (0.3 – 2) x 1014 cm-2 O VI : 8 x 1012 cm-2 observed: (3 - 8) x 1013 cm-2 Ionized dwarf-scale halo: columns Mgas = 9.5 x 105 Mʘ Column density [cm-2] Impact parameter [kpc]

  18. Summary: photoionized clouds • CHVC-scale models – not enough high-ions. • Dwarf-scale models -Match to observed metal columns requires: • Metallicity ~ 0.3 solar. • Low pressure ( ≤1 cm-3 K ). • Maximal ionizing spectrum. • Ionized starless “dwarf galaxies” could be detected as metal-ion absorbers. • Except for O VI→ collisional processes… Gnat & Sternberg 2004 ApJ, 608, 229

  19. Turbulent Mixing Layers log ( NCIV / NOVI ) Shock Ionization Conductive Interfaces Cooling Flows Fox et al. 2005 ApJ 630, 332 log ( NNV / NOVI ) Non-Equilibrium Collisional Processes?

  20. Non-Equilibrium Collisional Processes • Time scale for change in temperature: tTemp • Time scale for change in ionization state: tIonization • Non-equilibrium: tTemp<< tIonization tc (cooling) tH (heating) tr (cooling) ti (heating)

  21. Non-Equilibrium Collisional Processes? • Conductive Interfaces Surrounding Evaporating Clouds • Time-Dependent Radiative Cooling

  22. HI CHVC model cloud boundary: 1.3 kpc PHIM = 50 cm-3K THIM = 2x106 K (Galactic corona) photoionized cloud conductive interface Temperature [K] heat flow OVI HIM (hot) density [cm-3] CIV Radius [kpc] cloud evaporates Radius [kpc] Conductive interfaces – work in progress: • Non-equilibrium ionization in the flow. WIM (warm) to 2 CHVC radii: CIV central column ~10 times larger OVI central column ~106 times larger

  23. Non–Equilibrium Radiative Cooling • Cooling is faster than recombination(tc<<tr) • Gas stays “over-ionized” • Independent of gas density • Modified ionization affects cooling rates:for over-ionized gas cooling is suppressed • Cooling rate depends on metallicity

  24. H He C N O Ne Mg Si S Fe Rate coefficients (T) Coolingrate (xi) Numerical Computation • Cooling from CIE at T>5x106K. • Follow time-dependent ionizationdxi/dt=… ~ • Step 1: No Photoionization • dxi/dT independent of density • …But depends on metallicity • The energy equation (Cloudy Cooling) dT/dt=…

  25. time Results: Ionization - Hydrogen Equilibrium Non-Equilibrium 100 10-1 10-2 104 105 106 104 105 106 Temperature (K) Temperature (K) Recombination Lag

  26. Results: Ionization - Carbon Equilibrium Non-Equilibrium 100 10-1 10-2 104 105 106 104 105 106 Temperature (K) Temperature (K)

  27. Results: Ionization – Z dependence 100 equilibrium Z = 2 Z = 1 Z = 10-1 Z = 10-2 Z = 10-3 10-1 xOVI 10-2 10-3 104 105 106 Temperature (K)

  28. He Cooling Metal Line Cooling Hydrogen Cooling (Lya) Bremsstrahlung Results: CIE Cooling Z = 2 Z = 1 Z = 10-1 Z = 10-2 Z = 10-3 10-21 10-22 Leq (erg cm3 s-1) cooling efficiency 10-23 10-24 104 105 106 107 108 Temperature (K)

  29. Equilibrium Non-Equilibrium time Results: Non-Equilibrium Cooling

  30. Turbulent Mixing Layers log ( NCIV / NOVI ) Shock Ionization Conductive Interfaces Cooling Flows log ( NNV / NOVI ) Results: Diagnostic Ratios

  31. High Velocity Metal Absorbers Fox et al. 2005 ApJ, 630, 332

  32. Time-Dependent Cooling - Summary • Equilibrium and Non-EquilibriumIonization States and Cooling Efficiencies ofH, He, C, N, O, Ne, Mg, Si, S, & Fe,For 104 < T < 108 Kand 10-3 < Z < 2 solar. • Isochoric / Isobaric – conditions & results. • Impact of Self Radiation.

  33. Future Work • Photoionization by External Radiation • Cooling Columns in Flows • Applications - E.g.: • High-velocity ionized clouds &the Galactic Halo (E.g.: Sembach & Savage 92, Spitzer 1996) • IGM - WHIM (E.g.: Tripp et al. 00, Shull et al. 03, Richter et al. 03, Sembach et al. 04, Nicastro et al. 05, Savage et al. 05) • AGNs • Galaxy Clusters and Groups

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