EXPLORING CLUSTER ELLIPTIC GALAXIES AS COSMOLOGICAL STANDARD RODS

We explore the possibility of calibrating massive cluster elliptical g alaxies as cosmological standard rods using the fundamental plane rela tion combined with a correction for luminosity evolution. Although clu ster ellipticals certainly formed in a complex way, their passive evol ution out to redshifts of about 1 indicates that basically all major m erging and accretion events took place at higher redshifts. Therefore, a calibration of their luminosity evolution can be attempted. We prop ose to use the Mg-sigma relation for that purpose because it is indepe ndent of distance and cosmology. We discuss a variety of possible cave ats, ranging from dynamical evolution to uncertainties in stellar popu lation models and evolution corrections to the presence of age spread. Sources of major random and systematic errors are analyzed as well. W e apply the described procedure to nine elliptical galaxies in two clu sters at z = 0.375 and derive constraints on the cosmological model. F or the best-fitting Lambda-free cosmological model we obtain q(0) appr oximate to 0.1, with 90% confidence limits being 0 < q(0) < 0.7 (the l ower limit being due to the presence of matter in the universe). If th e inflationary scenario applies (i.e., the universe has flat geometry) , then, for the best-fitting model, matter and Lambda contribute about equally to the critical cosmic density (i.e., Omega(m) approximate to Omega(Lambda) approximate to 0.5). With 90% confidence, Omega(Lambda) should be smaller than 0.9.