Pere Tanguy speaks about the doctor who treated Vincent, when he was alive:
Pere Tanguy: I understand he's still close to the Van Gogh family. Maybe you should ask him why Vincent did it.
Armand: It's my father who wanted to know why. I just wanted to deliver this letter for him.
Pere Tanguy: The Van Gogh's are only ghosts in Paris now.
What does "ghosts" mean here?