Table 4
I Zw 18 model parameters.
| Parameter | MI,opt | MI,opt+IR | MNA | MNM | P08/L17 |
|---|---|---|---|---|---|
| w |  |
 |
 |
 |
|
 |
 |
 |
 |
||
 |
 |
 |
 |
||
 |
|||||
| U0 |  |
 |
 |
 |
|
 |
 |
 |
 |
||
 |
 |
 |
 |
||
 |
|||||
| n0 (log cm−3) |  |
 |
 |
 |
|
 |
 |
 |
 |
||
 |
 |
 |
 |
||
 |
|||||
| cut(a) |  |
 |
 |
 |
|
 |
 |
 |
 |
||
 |
 |
 |
 |
||
 |
|||||
| Z (log Z⊙) |  |
 |
 |
 |
−1.46 (P08; O/H) |
| Zdust(b) |  |
 |
 |
 |
|
| LX (log erg s−1) |  |
 |
 |
 |
|
| TX (log K) |  |
 |
 |
 |
|
| Q(H) (log s−1) |  |
 |
 |
 |
52.1 (P08; 18.2Mpc) |
| fesc(1 – ∞) (%) |  |
 |
 |
 |
≈63, [60, 70] (P08) |
| - fesc(1–1.8) (%) |  |
 |
 |
 |
|
| - fesc(1.8–4) (%) |  |
 |
 |
 |
|
| - fesc(4-20) (%) |  |
 |
 |
 |
|
| - fesc(20 + ∞) (%) |  |
 |
 |
 |
|
| MH+ (log M⊙) |  |
 |
 |
 |
6.5 (P08; 18.2Mpc) |
| MH0 (log M⊙) |  |
 |
 |
 |
≈[6.9–7.3] (L17) |
| MH2 (log M⊙) |  |
 |
 |
 |
|
| - MH2,C+ (log M⊙) |  |
 |
 |
 |
|
| - MH2,C (log M⊙) |  |
 |
 |
 |
|
| - MH2, CO (log M⊙) |  |
 |
 |
 |
|
| Mdust (log M⊙) |  |
 |
 |
 |
2.2 (L17), 2.86 ± 0.24(c) |
| fCII,H+ |  |
 |
 |
 |
|
| fCII,H |  |
 |
 |
 |
|
| fCII,H2 |  |
 |
 |
 |
Notes. Models MI,opt and MI,opt+IR considers ionized gas observations assuming P08’s modeling strategy without and with infrared lines respectively. MNA adds neutral atomic gas observations ([C ii], [O i], [Si ii], and [Fe ii]). MNM adds the CO marginal detection of Zhou et al. (2021) and upper limits on near-IR and mid-IR H2. The escape fractions are given for several energy ranges in Rydberg. The reported values correspond to the median of the posterior distribution together with the confidence interval. Combined quantities (e.g., MH2) are calculated for each draw and the final median value can therefore deviate from the combination of median values.(a) 1: ionization front (H+–H0 transition), 2: PDR front (H0–H2 transition), 3: C0–CO transition.(b) Dust-to-gas mass ratio. See Table 3 for more details.(c) Value from Rémy-Ruyer et al. (2015) assuming graphite composition.
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