Resolved using this post. Here is full working code:
int numOfDetectors=5; // number of desired histograms
// create histograms
TH1F** EDep=new TH1F*[numOfDetectors];
for (int i=0; i<numOfDetectors;i++) {
EDep[i] = new TH1F(TString::Format("%i_EDep_gm", i+1), TString::Format("Energy deposited by gamma events in det-%i", i+1), 1000, 0., 1000.);
}
// fill-in histograms
for (int i=0; i<numOfDetectors;i++){
EDep[i]->Fill(i+10);
}