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From HVCs to WHIM: Equilibrium & Non-Equilibrium Ionization in Metal Ion Absorbers. Orly Gnat & Amiel Sternberg Tel Aviv University ISRAEL. H I High-Velocity Clouds.  Wakker et al. 2003 ApJS, 146, 1. High-Velocity Metal Absorbers. Sembach et al. 2003, ApJ, 146, 165S.

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From HVCs to WHIM: Equilibrium & Non-Equilibrium Ionization in Metal Ion Absorbers

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From hvcs to whim equilibrium non equilibrium ionization in metal ion absorbers

From HVCs to WHIM:

Equilibrium & Non-Equilibrium

Ionization in

Metal Ion Absorbers

Orly Gnat & Amiel Sternberg

Tel Aviv University

ISRAEL


From hvcs to whim equilibrium non equilibrium ionization in metal ion absorbers

HI High-Velocity Clouds

 Wakker et al. 2003

ApJS, 146, 1


From hvcs to whim equilibrium non equilibrium ionization in metal ion absorbers

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, …)


From hvcs to whim equilibrium non equilibrium ionization in metal ion absorbers

Absorption toward Mrk 509 & PKS 2155-304

log column cm-2

C IV1548.2 Å 13.5 - >14.20

N V 1238.8 Å<13.08 - <13.24

Si III1012.5 Å 12.44 - 13.31

Si IV 1393.8 Å<12.33 - >13.44

S III 1190.2 Å<13.68 - <13.93

O VI1031.9 Å 13.56 - 13.93

Collins et al. 2004 ApJ, 605, 216


From hvcs to whim equilibrium non equilibrium ionization in metal ion absorbers

Key questions:

  • What are the photoionization properties of metals in minihalo clouds?

  • Are the HI CHVCs, dwarfs &

    ionized-absorbersrelated objects?


From hvcs to whim equilibrium non equilibrium ionization in metal ion absorbers

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


From hvcs to whim equilibrium non equilibrium ionization in metal ion absorbers

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


From hvcs to whim equilibrium non equilibrium ionization in metal ion absorbers

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


From hvcs to whim equilibrium non equilibrium ionization in metal ion absorbers

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]


From hvcs to whim equilibrium non equilibrium ionization in metal ion absorbers

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


From hvcs to whim equilibrium non equilibrium ionization in metal ion absorbers

  • 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),


From hvcs to whim equilibrium non equilibrium ionization in metal ion absorbers

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


From hvcs to whim equilibrium non equilibrium ionization in metal ion absorbers

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


From hvcs to whim equilibrium non equilibrium ionization in metal ion absorbers

IF

Warm

neutral

Hot

ionized

Warm

ionized

total H density

neutral H

Dwarf-scale halo: volume densities

density [cm-3]

Radius [kpc]


From hvcs to whim equilibrium non equilibrium ionization in metal ion absorbers

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]


From hvcs to whim equilibrium non equilibrium ionization in metal ion absorbers

Dwarf Model versus observations:

Nmodel / Nobserved

Impact parameter [kpc]


From hvcs to whim equilibrium non equilibrium ionization in metal ion absorbers

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]


From hvcs to whim equilibrium non equilibrium ionization in metal ion absorbers

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


From hvcs to whim equilibrium non equilibrium ionization in metal ion absorbers

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?


From hvcs to whim equilibrium non equilibrium ionization in metal ion absorbers

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)


From hvcs to whim equilibrium non equilibrium ionization in metal ion absorbers

Non-Equilibrium Collisional Processes?

  • Conductive Interfaces Surrounding Evaporating Clouds

  • Time-Dependent Radiative Cooling


From hvcs to whim equilibrium non equilibrium ionization in metal ion absorbers

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


From hvcs to whim equilibrium non equilibrium ionization in metal ion absorbers

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


From hvcs to whim equilibrium non equilibrium ionization in metal ion absorbers

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=…


From hvcs to whim equilibrium non equilibrium ionization in metal ion absorbers

time

Results: Ionization - Hydrogen

Equilibrium

Non-Equilibrium

100

10-1

10-2

104

105

106

104

105

106

Temperature (K)

Temperature (K)

Recombination Lag


From hvcs to whim equilibrium non equilibrium ionization in metal ion absorbers

Results: Ionization - Carbon

Equilibrium

Non-Equilibrium

100

10-1

10-2

104

105

106

104

105

106

Temperature (K)

Temperature (K)


From hvcs to whim equilibrium non equilibrium ionization in metal ion absorbers

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)


From hvcs to whim equilibrium non equilibrium ionization in metal ion absorbers

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)


From hvcs to whim equilibrium non equilibrium ionization in metal ion absorbers

Equilibrium

Non-Equilibrium

time

Results: Non-Equilibrium Cooling


From hvcs to whim equilibrium non equilibrium ionization in metal ion absorbers

Turbulent

Mixing

Layers

log ( NCIV / NOVI )

Shock

Ionization

Conductive

Interfaces

Cooling

Flows

log ( NNV / NOVI )

Results: Diagnostic Ratios


From hvcs to whim equilibrium non equilibrium ionization in metal ion absorbers

High Velocity Metal Absorbers

Fox et al. 2005

ApJ, 630, 332


From hvcs to whim equilibrium non equilibrium ionization in metal ion absorbers

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.


From hvcs to whim equilibrium non equilibrium ionization in metal ion absorbers

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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