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Table 3

Parametersa for the RADEX modeling of the H3O+ Line.

Galaxy Source sizeb T IR N(H3O+)c fit X(H3O+)d
[″] [K] [cm-2]

IC 342 13 40 1.25 × 1014 4 × 10-9
NGC 253 13 50 2.25 × 1015 1.5 × 10-8
NGC 1068 2 150 1 × 1015 1 × 10-8
NGC 4418 0.5 80 2.5 × 1016 3 × 10-8
NGC 6240 1 50 5 × 1015 2.5 × 10-8

Notes. 

(a)

The temperature range investigated for all galaxies was 10–500 K, but solutions were fixed where Tex = TIR. The N(H3O+) range searched was 1012 − 1017 cm-2.

(b)

For a discussion of adopted source sizes see Sect. 2.

(c)

The total beam-averaged column density of H3O+ is 2–3 times higher than that of p-H3O+ in Fig. 2, because the ortho to para ratio of H3O+ drops from the high-temperature limit of o/p = 1 for T > 100 K to o/p = 2 when T < 50 K. Here we have corrected column densities for an o/p ratio of 1.5.

(d)

IC 342: N(H2) is estimated to 3 × 1022 cm-2 (from the CO data of Eckart et al. 1990). NGC 253: N(H2) is estimated to 1.3 × 1023 cm-2 (using CO data from Mauersberger et al. (1996). NGC 1068: From Tacconi et al. (1994) the N(H2) for the CND is estimated to be 2 − 10 × 1022 cm-2. If we take the CO 2–1 data from Planesas et al. (1989) and assume a source size of 2″ we obtain N(H2) = 1.35 × 1023 cm-2. NGC 4418: Column density for H2 for a 0''̣5 CO 2–1 source size is N(H2) = 7.4 × 1023 cm-2 (Costagliola et al. in prep.). NGC 6240: Iono et al. (2007) estimate N(H2) to 1 × 1023 cm-2 from their CO 3–2 data.

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