Sony use to own these two studious now Sony dont own them?
Team Ico made ico shadow of colossos and last guardian
Team Gravity made gravity rush series
They are simply part of Japan Studio. Team Ico and Team Gravity are not actual defined studios per se, but rather teams that operate within Japan Studio.
Because of this, these teams are not forever existing. They are not Polyphony, or Media Molecule, or Naughty Dog. They are just teams that exist to make certain games that define their current project outlook.
Team Ico doesn't exist anymore. It's gone.
Team Gravity might still exist, but that depends entirely on what Toyama (the director of games made by this team) is making. The team was originally Project Siren and will continue to morph.
It is essentially how Nintendo works, but they keep their team names fixed, since theirs do not refer to actual game projects.