The evolution of barred spiral galaxies in the Hubble Deep Fields North and South

The frequency of barred spiral galaxies as a function of redshift contains important information on the gravitational influence of stellar discs in th eir dark matter haloes and may also distinguish between contemporary theori es for the origin of galactic bulges. In this paper we present a new quanti tative method for determining the strength of barred spiral structure, and verify its robustness to redshift-dependent effects. By combining galaxy sa mples from the Hubble Deep Field North with newly available data from the H ubble Deep Field South, we are able to define a statistical sample of 46 lo w-inclination spiral systems with I-814W < 23.2 mag, Analysing the proporti on of barred spiral galaxies seen as a function of redshift, we find a sign ificant decline in the fraction of barred spirals with redshift, The redshi ft distribution of 22 barred and 24 non-barred spirals with suitable inclin ations is inconsistent with their being drawn from the same distribution at the 99 per cent confidence level. The physical significance of this effect remains unclear, but several possibilities include dynamically hotter (or increasingly dark-matter-dominated) high-redshift discs, or an enhanced eff iciency in bar destruction at high redshifts, By investigating the formatio n of the 'orthogonal' axis of Hubble's classification tuning fork, our resu lt complements studies of evolution in the early-late sequence, and pushes to later epochs the redshift at which the Hubble classification sequence is observed to be in place.