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!!!