How to get all hashtags

[Cteq3132]

Hello ! I have a question : I've looked through the doc, and I don't see if there is a way of getting all the names of a feed group. For example if I have a feed group named topic and I publish two activities this way :

{
    "actor": "user:1",
    "object": "I love #computers ^^"
    "verb": "tweet",
    "to": ["topic:computers"]
}

{
    "actor": "user:2",
    "object": "I love #animals ^^"
    "verb": "tweet",
    "to": ["topic:animals"]
}

Is there a way to get a list containing [computers, animals] with the API ?