Top-left: FoV of GTC/OSIRIS showing Holm 15A (blue circle), J004150 (red circle) and slit positions in green rectangles. 1D spectra of Holm 15A (top-right) and J004150 (bottom-left). Bottom-right: spectral decomposition for the Mg II line of J004150 (top subpanel): original data in black, power-law continuum in blue and combined best-fit model (continuum + UV Fe II template + narrow-line component + broad-line component) in red. Individual broad-line Gaussians are the orange dashed lines and the total broad component is the orange solid line; individual narrow-line Gaussians are the green dashed lines and the total narrow component is the cyan line; Fe II template is the magenta line; lower subpanel shows residuals (gray) between the combined best-fit model and original data.