J0841+01. GTC continuum (left) and Hα images (middle). Contour values start at 3σ and increase with factor ×2. For the Hα image, σ = 4.1 × 10⁻¹⁹ erg⁻¹ cm⁻² pixel⁻¹. QSO2 and C indicate the QSO2 and the companion galaxy. TDG is a tidal dwarf galaxy candidate (see text). The small right panel zooms in the central region of the HST WFC3/UVIS F438W image, which contains the [OII]λ3727 doublet. The intricate filamentary structures between the two galaxies are dominated by gas emission. They are reminiscent of a giant ionised bubble. In this and all figures the Hα images have been continuum subtracted. Also, N is always up and E is left.