A spatially resolved study of ionized regions in galaxies at different ...
A spatially resolved study of ionized regions in galaxies at different ... A spatially resolved study of ionized regions in galaxies at different ...
166 Appendix B Argon For argon, the [Ariii] 7136 Å line is used: 12 + log(Ar 2+ /H + ) = log ( ) I(7136) + 6.157 + 0.808 − 0.508 · log t I(Hβ) t In this case, the approximation t([Ariii]) ≈ t([Siii]) is normally followed. Iron In the case of iron, the [Feiii] λ 4658 Å emission line is used to derive the ionic abundance of the iron twice ionized, using the electron temperature of [Oiii]. Care has to be taken because this line is in the region where the blue bump of the Wolf-Rayet feature lies. Izotov et al. (1994), using emissivities by Garstang et al. (1978), derived: N(F e ++ ) N(H + ) = 2.3 × 10 −6 1.387 t −0.983 10 −0.0424/t√ 1.34/t I(λ4658) t 10 I(Hβ) which can be written in the functional form given by Pagel et al. (1992) as: 12 + log(F e 2+ /H + ) = log ( ) I(4658) + 6.504 + 1.298 − 0.483 · log t I(Hβ) t Helium Helium lines, as hydrogen ones in the visible spectrum, arise mainly from pure recombination, although they have some contribution from collisional excitation and be affected by self-absorption. There are many of them, but usually blended with other lines. The ones generally used are Hei λλ 4471, 5876, 6678 and 7065Å, and Heii λ 4686Å to estimate the helium abundances once and twice ionized respectively. Normally, the [Oiii] temperature is adopted as representative of the helium zone. Olive and Skillman (2001) carried out a very thorough study to determinate all the contributions to the helium lines. In that work, the helium intensities are scaled to Hβ and the singly ionized helium abundance is given by: y + (λ) = I(λ) E(Hβ) I(Hβ) E(λ) ( W (λ) + aHei W (λ) ) 1 1 1 + γ f(τ) where E(λ)/E(Hβ) is the theoretical emissivity scaled to Hβ and W(λ) the equivalent width. The last expression also contains a correction factor for underlying stellar absorption, parametrized by a Hei , a density dependent collisional correction factor, (1 + γ) −1 , and a fluorescence correction which depends on the optical depth τ. The theoretical emissivities scaled to Hβ are taken from Smits (1996):
B • Physical conditions of the gas and abundances 167 E(Hβ)/E(4471) = 2.0094T 0.1259 E(Hβ)/E(5876) = 0.7355T 0.2298 E(Hβ)/E(6678) = 2.5861T 0.2475 E(Hβ)/E(7065) = 4.3588T −0.3456 For the collisional correction γ, the expressions taken from Kingdon and Ferland (1995): γ(4471) = (6.95T 0.15 e −4.545/T + 0.22T −0.55 e −4.884/T + 0.98T −0.45 e −4.901/T )/D γ(5876) = (6.78T 0.07 e −3.776/T + 1.67T −0.15 e −4.545/T + 0.60T −0.34 e −4.901/T )/D γ(6678) = (3.15T −0.54 e −3.776/T + 0.51T −0.51 e −4.545/T + 0.20T −0.66 e −4.901/T )/D γ(7065) = (38.09T −1.09 e −3.364/T + 2.80T −1.06 e −3.699/T )/D where D = 1 + 3130n −1 T −0.50 . The corrections for fluorescence are given in terms of the optical depth: f(4471) = 1 + 0.001τ f(5876) = 1 + 0.0049τ f(6678) = 1 f(7065) = 1 + 0.4τ 0.55 which, as it can be seen, are close to 1. used: For the helium twice ionized, the equation found by Kunth and Sargent (1983) can be y 2+ (4686) = (0.065 + 0.024t − 0.0052t 2 ) I(λ4686) I(Hβ)
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- Page 180 and 181: 160 Appendix A where c=0.434C. This
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- Page 210 and 211: 190 REFERENCES Bertelli, G., Bressa
- Page 212 and 213: 192 REFERENCES Girardi, L. & Bertel
- Page 214 and 215: 194 REFERENCES Kunth, D. & Sargent,
- Page 216 and 217: 196 REFERENCES Pérez-Montero, E.,
- Page 218 and 219: 198 REFERENCES Terlevich, R., Melni
B • Physical conditions <strong>of</strong> the gas and abundances 167<br />
E(Hβ)/E(4471) = 2.0094T 0.1259<br />
E(Hβ)/E(5876) = 0.7355T 0.2298<br />
E(Hβ)/E(6678) = 2.5861T 0.2475<br />
E(Hβ)/E(7065) = 4.3588T −0.3456<br />
For the collisional correction γ, the expressions taken from K<strong>in</strong>gdon and Ferland (1995):<br />
γ(4471) = (6.95T 0.15 e −4.545/T + 0.22T −0.55 e −4.884/T + 0.98T −0.45 e −4.901/T )/D<br />
γ(5876) = (6.78T 0.07 e −3.776/T + 1.67T −0.15 e −4.545/T + 0.60T −0.34 e −4.901/T )/D<br />
γ(6678) = (3.15T −0.54 e −3.776/T + 0.51T −0.51 e −4.545/T + 0.20T −0.66 e −4.901/T )/D<br />
γ(7065) = (38.09T −1.09 e −3.364/T + 2.80T −1.06 e −3.699/T )/D<br />
where D = 1 + 3130n −1 T −0.50 . The corrections for fluorescence are given <strong>in</strong> terms <strong>of</strong> the<br />
optical depth:<br />
f(4471) = 1 + 0.001τ<br />
f(5876) = 1 + 0.0049τ<br />
f(6678) = 1<br />
f(7065) = 1 + 0.4τ 0.55<br />
which, as it can be seen, are close to 1.<br />
used:<br />
For the helium twice <strong>ionized</strong>, the equ<strong>at</strong>ion found by Kunth and Sargent (1983) can be<br />
y 2+ (4686) = (0.065 + 0.024t − 0.0052t 2 ) I(λ4686)<br />
I(Hβ)
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