Context. The evolution of quasar host galaxies is still hardly studied at high redshifts (z > 2), although this is a very interesting redshift range as both the quasar activity and the star formation rate density have their peak at z ≈ 2–3. This makes is especially interesting to study properties of quasar host galaxies, such as the star formation rate or the black hole mass at this redshift. A...

The lens candidate RXJ 0921+4529 consists of two z s = 1.66 quasar separated by 6. ′′ 93 with an H band magnitude difference of ∆m = 1.39. The lens appears to be a z l = 0.31 X-ray cluster, including a m H =18.5 late-type galaxy lying between the quasar images. We detect an extended source overlapping the faint quasar but not the bright quasar. If this extended source is the host galaxy of the ...

In this second paper, in a series of two, we determine the properties of the stellar torus that we showed in the first paper to result as a product of two merging black holes. If the surrounding stellar cluster is as massive as the binary black hole, the torque acting on the stars ejects a fraction which extracts the binary’s angular momentum. After the black holes coalesced on scales of ∼ 10 y...