Spectacular 240 kpc double-sided relativistic jets in a spiral-hosted narrow-line Seyfert 1 galaxy

Narrow-line Seyfert 1 (NLS1) galaxies are a peculiar sub-class of active galactic nuclei (AGNe). They have demonstrated that the presence of relativistic jets in an AGN is not strictly related to its radio-loudness, the black hole mass, or their host galaxy type. Here, we present a remarkable example of a radio-quiet NLS1, 6dFGS gJ035432.8a- 134008 (J0354a- 1340). In our Karl G. Jansky Very Large Array observations at 5.5 GHz, the source shows a bright core with a flat spectral index and extended emission corresponding to very elongated jets. These are the largest double-sided radio jets found to date in an NLS1, with a de-projected linear size of almost 250 kpc. We also analysed near-infrared and optical images obtained by the Magellan Baade and the European Southern Observatory New Technology Telescope. By means of photometric decomposition and colour maps, we determined that J0354a- 1340 is hosted by a spiral or disc-like galaxy. Fully evolved relativistic jets have traditionally been associated with high-mass elliptical galaxies hosting the most massive black holes. Instead, our results confirm that powerful jets can also be launched and sustained by less massive black holes in spiral galaxies, implying that the launching of the jets is governed by factors other than those previously believed to be at play.