The only thing that remains is to create a new Topic (Resources > JMS > Topics > New) ,in which to choose the topic space you want to use, which in your case is Default.Topic.Space. After that you can send a message to your topic using code like this:
// Get the connection factory
connFactory=(ConnectionFactory)initCtx.lookup("jms/mycf");
// Get the destination used to send a message
destination = (Destination)initCtx.lookup("jms/mytopic");
Connection conn = connFactory.createConnection();
// Create a non-transacted session
Session session = conn.createSession(false, Session.AUTO_ACKNOWLEDGE);
// Create the message producer
MessageProducer msgProducer = session.createProducer(destination);
// Create the message
TextMessage txtMsg = session.createTextMessage("Hello There!!!");
// Send the message
msgProducer.send(txtMsg);
session.close();
conn.close();