The Hubble diagram of quasars and the deceleration parameter q o

Abstract

On the assumption that the universe can be described by the Friedmann model and the quasar redshifts are mainly cosmological, the Hubble diagrams of different types of quasars have been discussed. The main conclusions are as follows: 1. (1) The curve-fitting solution of redshift-apparent-magnitude relation shows that the values of deceleration parameter q 0 derived from four types of quasars are all > 1 2 , being∼+1 − ∼+30. 2. (2)26 quasars with resolved radio components, steep radio spectrum (power index ⩽ −0.6) give q 0 = 29 ± 3. 27 quasars with strong interplanetary scintillation ( R ⩾ 0.4), give q 0 = 2.6 ± 0.2. 24 quasars with amplitude of light variation no greater than O m.5 give q 0 = 6.5 ± 0.5. Lastly, 8 compact radio quasars resolved with VBLI give q 0 = 1.6 ± 0.1. The corresponding weighted solutions are q 0 = 36 ± 5, 1.6 ± 0.1, 5.2 ± 0.4 and 0.7 ± 0.1 respectively. These values of q 0 may be affected by their different intrinsic luminosity evolution. The correction of luminosity evolution should be taken into account in looking for the true value of q 0 3. (3) It is necessary to use the strict redshift-apparent-magnitude relation when deriving q 0 from the Hubble diagram of quasars.