THE MUENSTER REDSHIFT PROJECT - III - OBSERVATIONAL CONSTRAINTS ON THE DECELERATION PARAMETER

The redshift-volume test for determining the deceleration parameter q( 0) is applied to 89,125 galaxies with redshifts z less than or equal t o 0.2 (redshift errors sigma(z) = 0.031) and magnitudes 14.0 less than or equal to r(F) less than or equal to 18.0 mag, obtained within the Muenster Redshift Project (MRSP). With samples of this size, cosmic cu rvature effects can be measured even at intermediate redshifts. Compar atively small z-values and red photometric magnitudes assure that bias ed object selection and galaxy evolution do not affect the measurement s in uncontrolled ways. In the first step of our analysis, the redshif t-volume test assumes a minimum model of passive galaxy evolution. For the cosmological constant Lambda = 0 and for the evolutionary models of Rocca-Volmerange gr Guiderdoni, the total sample yields the deceler ation parameter q(0) = 0.10 with the 95% confidence limit, q(0) < 0.75 . In a second step, we evaluate-within the errors of the first step-wh ether our q(0)-value is over- or underestimated, using those observed evolutionary trends that appear to be nearly q(0) independent. The tre nds indicate that our result q(0) = 0.10 can be regarded as an upper l imit. Effects of incompleteness, errors in the (K + E)-corrections due to extreme galaxy mixtures, as well as different models of population synthesis, large-scale clustering, galactic reddening, and gravitatio nal lensing, are discussed. We conclude that the combination of MRSP r edshift data, observed evolutionary trends in the galaxy luminosity fu nctions, and passive galaxy aging suggests an open universe.