PHL 6625: A Minor Merger-associated QSO Behind NGC 247

Abstract

PHL 6625 is a luminous quasi-stellar object (QSO) at z  = 0.3954 located behind the nearby galaxy NGC 247 ( z = 0.0005). Hubble Space Telescope observations revealed an arc structure associated with it. We report on spectroscopic observations with the Very Large Telescope and multiwavelength observations from the radio to the X-ray band for the system, suggesting that PHL 6625 and the arc are a close pair of merging galaxies, instead of a strong gravitational lens system. The QSO host galaxy is estimated to be (4–28) × 10 10 M ☉ and the mass of the companion galaxy is estimated to be M *  = (6.8 ± 2.4) × 10 9 M ☉ , suggesting that this is a minor merger system. The QSO displays typical broad emission lines, from which a black hole mass of about (2–5) × 10 8 M ☉ and an Eddington ratio of about 0.01–0.05 can be inferred. The system represents an interesting and rare case where a QSO is associated with an ongoing minor merger, analogous to Arp 142.