Ionization composition of dwarf galaxies

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!!!