Near-IR diagnostic diagrams analyzed in this paper: Top row: [S III]/Paγ as a function of [Fe II]/Paβ (Fe2S3–β), [Fe II]/Paα (Fe2S3–α), [P II]/Paβ (P2S3), and [C I]/Paβ (C1S3). AGN models are represented as circles, colored as a function of log(U), and with sizes increasing with density. Star-forming models are the triangle symbols. The maximum AGN line and the maximum starburst separation limit are defined by a dotted red line and a continuous blue line, respectively. Bottom row: same as above but as a function of the [S III]/Paβ line ratio on the y-axis.