2016MNRAS.461.2374C

Using detailed modelling, we analyse the spectra observed from the sample galaxies at z ∼ 0.8 presented by Ly et al., constraining the models by the [O iii]5007+4959/[O iii]4363 line ratios. Composite models (shock + photoionization) are adopted. Shock velocities >=100 km/s and pre-shock densities n₀ ∼ 200/cm3 characterize the gas surrounding the starburst (SB), while n₀ are higher by a factor of 1.5-10 in the AGN emitting gas. SB effective temperatures are similar to those of quiescent galaxies (T_* ∼ 4-7 x 10⁴ K). Cloud geometrical thicknesses in the SB are <=10¹⁶ cm, indicating major fragmentation, while in AGN they reach >10 pc. O/H are about solar for all the objects, except for a few AGN clouds with O/H=0.3-0.5 solar. SB models reproduce most of the data within the observational errors. About half of the objects' spectra are well fitted by an accreting AGN. Some galaxies show multiple radiation sources, such as SB + AGN, or a double AGN.