Extended Data Fig. 3: BPT (Baldwin, Phillips & Terlevich) diagram, showing galaxy type (HII star forming region, AGN, LINER, composite) as a function of certain line flux ratios.
From: Monthly quasi-periodic eruptions from repeated stellar disruption by a massive black hole
The line ratios are [O iii] 5007 / Hβ versus [N ii] 6583 / Hα (left) and [S ii] 6717,6732 / Hα (right). In both panels, the red solid lines are the theoretical models separating star-forming regions and AGN40,41,42,43. In the left panel, the green line is the demarcation between pure star forming and composite star-forming/AGN regions, as prescribed by. The straight segments separate proper AGN from LINERs. The SDSS galaxy catalogue object density is shown in greyscale and the position of 2MASX J02301709+2836050 is marked by the blue cross (errorbars are 1-σ).
