Baldwin-Phillips-Terlevich (BPT) diagram (Baldwin et al. 1981) for luminous compact galaxies (LCGs) from SDSS DR7 (Izotov et al. 2011a) (small blue circles). HG 031203 (this paper) is shown by a large filled red star. The five low-metallicity AGNs from Izotov & Thuan (2008) and Izotov et al. (2010) are indicated by large filled black circles. Host galaxy (HG) 031203 for any data is shown by a star. Other HGs are denoted as follows (see text for details): Savaglio et al. (2009): filled green squares, Levesque et al. (2010a): filled light blue squares, (Christensen et al. 2008): violet asterisks, Hammer et al. (2006): large green open circles, (Wiersema et al. 2007): filled purple triangle, Han et al. (2010): purple diamonds, Margutti et al. (2007): filled purple star, Prochaska et al. (2004): open blue star, Watson et al. (2010): open yellow star. All HGs with emission line fluxes lower than 2  ×  10^-17 erg s^-1 cm^-2 are shown by small symbols. Also, the 100 000 emission-line galaxies from SDSS DR7 selected by Izotov et al. (2011a) are shown by grey dots. The dashed line represents the empirical line of Kauffmann et al. (2003) that separates galaxies dominated either by star formation or by an AGN. The continuous line shows the upper limit for purely star-forming galaxies (SFGs) from Stasińska et al. (2006). (A colour version of this figure is available in the online journal.)