High-velocity outflows from AGN are a well-known phenomena in terms of the Broad Absorption Lines seen in the UV/optical .
More recently , similar , possibly related , outflows have been reported in the X-ray .
The most extreme example is seen in the nearby , luminous QSO PDS 456 , which displays a massive , high velocity ( 50000 km s ^ { -1 } ) , high-ionization X-ray outflow of 10 { M } _ { \odot } yr ^ { -1 } .
Here we present the UV spectrum of PDS 456 as observed by the Hubble Space Telescope .
We find the UV spectrum is also extreme , displaying very broad emission-lines , with C iv \lambda 1549 blueshifted by 5000 km s ^ { -1 } and a broad Ly \alpha absorption trough blueshifted by 14000–24000 km s ^ { -1 } .
No strong , broad high-ionization absorption features are seen .
We interpret the combined UV and X-ray spectrum of PDS 456 as the signature of a decelerating , cooling outflow , which may be driven by radiation and/or magnetic field .
This outflow may be the source of some of the broad emission and absorption-line gas .