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Register a new userPHL 6625: A Minor Merger-Associated QSO Behind NGC 247
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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 (HST) observations revealed an arc structure associated with it. We report on spectroscopic observations with the Very Large Telescope (VLT) 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) x 10^10 M_sun, and the mass of the companion galaxy of is estimated to be M_* = (6.8 +/- 2.4) x 10^9 M_sun, 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) x 10^8 M_sun 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.
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Deep optical imaging with both Hyper Suprime-Cam and Suprime-Cam on the 8.2 m Subaru Telescope reveals a number of outer faint structures around the archetypical Seyfert galaxy NGC 1068 (M 77). We find three ultra diffuse objects (UDOs) around NGC 1068. Since these UDOs are located within the projected distance of 45 kpc from the center of NGC 1068, they appear to be associated with NGC 1068. Hereafter, we call them UDO-SW, UDO-NE, and UDO-SE where UDO = Ultra Diffuse Object, SW = south west, NE = north west, and SE = south east; note that UDO-SE was already found in the SDSS Stripe 82 data. Among them, both UDO-NE and UDO-SW appear to show a loop or stream structure around the main body of NGC 1068, providing evidence for the physical connection to NGC 1068. We consider that UDO-SE may be a tidal dwarf galaxy. We also find another UDO-like object that is 2 magnitudes fainter and smaller by a factor of 3 to 5 than those of the three UDOs. This object may belong to a class of low surface brightness galaxy. Since this object is located along the line connecting UDO-NE and UDO-SW, it is suggested that this object is related to the past interaction event that formed the loop by UDO-NE and UDO-SW, thus implying the physical connection to NGC 1068. Another newly-discovered feature is an asymmetric outer one-arm structure emanated from the western edge of the outermost disk of NGC 1068 together with a ripple-like structure at the opposite side. These structures are expected to arise in a late phase of a minor merger according to published numerical simulations of minor mergers. All these lines of evidence show that NGC 1068 experienced a minor merger several billions years ago. We then discuss the minor-merger driven triggering of nuclear activity in the case of NGC 1068.
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