Unable to subscribe after forkjoin

I want to perform some firebase operation inside a loop in angular. When I send an HTTP request to firebase it returns an array of observables so using forkjoin i convert this array of observables into single observables. Now the problem is when I subscribe to these new observables I didn't get anything

  get_student_email() {
    this.get_project_service
      .get_project_by_doc_id(this.batchID, this.projectID)
      .subscribe((res) => {
        this.response = res;
        this.email = this.response.student;
        let data = this.email.map((email) =>
          this.get_student_service.get_student_by_email_id(email)
        );
        let info = forkJoin([data]);
        console.log('info:', info);
        info.subscribe((res) => {
          console.log(res);
          console.log('Execute');
        });
      });
  }

Output:info: Observable {_isScalar: false, _subscribe: ƒ}

I also try this. In this time it again returns observables

 let data = this.email.map((email) =>
          this.get_student_service.get_student_by_email_id(email)
        );

        let info = forkJoin([data]);
        console.log('info:', info);
        info.subscribe((res) => {
          console.log(res);
          console.log('Execute');
        });
      });

Output:-
info: Observable {_isScalar: false, _subscribe: ƒ}
[Observable]
Execute

Here is my service

  get_student_by_email_id(email) {
    return this.fire_store
      .collection('User', (ref) => ref.where('email', '==', email))
      .valueChanges();
  }

I don't know what is the main reason behind this problem. What I want is that after loop complete its execution it return single array object contain information about all the user which belongs to that email array(this.email)