Ionization composition of dwarf galaxies

Evgenii Vasiliev

Institute of Physics, Southern Federal University, Rostov on Don

observations of metals in blue compact dwarfsAloisi et al 2003 – Zw18: NI, OI, FeII, SiIILebouteiller et al 2004 – Zw 36: CII, NI, OI, SiII, FeII,

CIII, NII, FeIII, OVI Vilchez & Iglesias-Paramo 2003 - 22 BCDs

photoizined gas in DM minihalos Gnat & Sternberg 2004

neutral cores: OI, NI, CII, SiIIionized shielding envelopes: CIV, NV, OVI

background

collisional ionization equilibrium (CIE) Cox & Tucker 1969, Raymond et al. 1976, Shull & van Steenberg 1982, Gaetz & Salpeter 1983, Sutherland & Dopita 1993, Benjamin et al. 2001

non-equlibrium (time-dependent) radiative cooling Kafatos 1976, Shapiro & Moore 1976, Edgar & Chevalier 1986, Schmutzler & Tscharnuter 1993, Sutherland & Dopita 1993, Gnat & Sternberg 2007

calculations of the cooling rates of astrophysical plasma

strong difference between equlibrium and non-equilibrium cooling rates & ionization states

Gnat & Sternberg 2007

presence of UV radiation equlibrium

strong suppression of the cooling rates of H+He plasma Efstathiou (1992) enriched gas Wiersma et al. (2008) - EQ

calculations of the cooling rates of astrophysical plasma

equlibrium ~ non-equilibrium a) low metallicityb) high ionizing fluxc) low density

or b) + c) high ionization parameter

non-equilibrium collisional rates (dash)

equilibrium photo rates (dot)non-equilibrium photo rates

(solid)

EV, in preparation

equlibrium or non-equilibrium: example

DWs: number densities 10-3 – 10-2 cm-3 & low flux

transition from EQ to NEQ

non-e

quili

bri

um

colli

sional st

ate

– b

lack

solid

non

-eq

uilib

riu

m p

hoto

sta

te -

colo

r

NEQ collisional

n = 10-4 cm-3

n = 10-3 cm-3

n = 10-2 cm-3

EQ

N

EQ

EV et al., in preparation

the ionization and thermal evolution of a lagrangian element optically thin for external ionizing radiation all ionization states of the elements H, He, C, N, O, Ne and Fe

major processes: photoionization

(Verner et al. 1996, Vener & Yakovlev 1995, Kaastra & Mewe 1993)

collisional ionization (Voronov 1997) radiative and dielectronic recombination

(Shull & van Steenberg 1982, Mazzotta et al. 1998) charge tranfer in collisions with hydrogen and helium atoms and

ions (Arnaud & Rothenflug 1985, Kingdon & Ferland 1996)

total cooling and heating rates are calculated using the photoionization code CLOUDY as subroutine

solve a set of 68 coupled equations

atomic data and model description

ionizing radiation:

local universe – extragalactic background z = 0

(Haardt & Madau 1996, 2001)

ionizing background

10x

4x

2x

1x

carbon ionization states: example

non-e

quili

bri

um

colli

sional st

ate

- b

lack

non

-eq

uilib

riu

m p

hoto

sta

te -

colo

r

1x

2x

4x

10x

carbon ionization states: example

non-e

quili

bri

um

colli

sional st

ate

- b

lack

non

-eq

uilib

riu

m p

hoto

sta

te -

colo

r

1x

2x

4x

10x

ionization state ratios

n = 10-4 cm-3 - dot

n = 10-3 cm-3 - solid

n = 10-2 cm-3 - dash

decr

ease

dens

ity

NEQ collisional [Z] = 0

[Z] = 0

[Z] = -1

[Z] = -3

Neq

Eq

non-e

quili

bri

um

colli

sional st

ate

- b

lack

non

-eq

uilib

riu

m p

hoto

sta

te -

colo

rionizing radiation: extragalactic background z = 0 (Haardt & Madau 1996, 2001)

ionization state ratios

Vilchez & Iglesias-Paramo 2003

ionization state ratios

tem

pera

ture

-2,0 -1,5 -1,0 -0,5 0,0 0,5

-1,5

-1,0

-0,5

0,0

0,5

1,0

log

([O

III]/[

OII]

)

log ([NII]/[OII])

[Z] = -3 [Z] = -1 [Z] = 0 colls [Z] = 0

1E4

2E4

5E4

1E5

3E5

the strong difference between equilibrium and non-equilibrium ionization states (& cooling rates) can be important for modeling ionic composition in dwarf galaxies;

study ionic ratios for different stellar population spectra;

incorporation of ionic state & cooling rate calculations into gas dynamics.

conclusion & future

thank you!!!