Photon leaking or very hard ionizing radiation? Unveiling the nature of He II-emitters using the softness diagram

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Table 1.

Mean offsets and standard deviation of the residuals of the resulting properties derived by HCM-TEFF when the model emission lines are used as input as a function of the used emission-line ratios.

Used line ratios	T_* (kK) ^(a)		log U^(a)		log f_abs^(b)		log U^(b)
	Mean Δ	σ res.	Mean Δ	σ res.	Mean Δ	σ res.	Mean Δ	σ res.
[O II]/[O III], [S II]/[S III], He I/He II	+0.8	2.1	+0.01	0.10	+0.11	0.34	−0.10	0.53
[O II]/[O III], He I/He II	+0.8	2.1	+0.01	0.10	−0.12	0.27	+0.14	0.47
[S II]/[S III], He I/He II	+0.6	2.0	+0.03	0.13	−0.19	0.35	+0.10	0.62
[S II]/[O III], He I/He II	−0.3	5.1	+0.04	0.51	−0.07	0.27	−0.10	0.59
He I/He II	−0.5	6.8	+0.04	0.72	−0.12	0.35	−0.25.	0.63

Notes.

^(a)

From models using black-body SEDs.

^(b)

From models using BPASS v.2.1 for Z_* = Z_g, x = −1.35 and M_up = 300 M_⊙ SEDs and density-bounded geometry.

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