TF2 *f1a = new TF2("f1a","ROOT::Math::cauchy_pdf(x, y)",0,10,0,10);
TF2 *f2a = new TF2("f2a","ROOT::Math::chisquared_pdf(x,y)",0,20, 0,20);
TF2 *f3a = new TF2("f3a","ROOT::Math::gaussian_pdf(x,y)",0,10,0,5);
TF2 *f4a = new TF2("f4a","ROOT::Math::tdistribution_pdf(x,y)",0,10,0,5);

TCanvas *c1 = new TCanvas("c1","c1",800,650);

c1->Divide(2,2);

c1->cd(1); f1a->SetLineWidth(1);
f1a->Draw("surf1");
c1->cd(2); f2a->SetLineWidth(1);
f2a->Draw("surf1");
c1->cd(3); f3a->SetLineWidth(1);
f3a->Draw("surf1");
c1->cd(4); f4a->SetLineWidth(1);
f4a->Draw("surf1");

gROOT->GetListOfCanvases()->Draw()