Evolution and Impact of Bars over the Last Nine Gyr: Early Results from GEMS

Bars drive the dynamical evolution of disk galaxies by redistributing mass and angular momentum, and they are ubiquitous in present-day spirals. Early studies of the Hubble Deep Field reported a dramatic decline in the rest-frame optical bar fraction f_(opt) to below 5% at redshifts z > 0.7, implying that disks at these epochs are fundamentally different from present-day spirals. The GEMS bar project, based on ~ 10,000 galaxies with HST-based morphologies and accurate redshifts over the range 0.2–1.3, aims at constraining the evolution and impact of bars over the last 9 Gyr. We present early results indicating that f_(opt) remains ~ constant with a lower limit of ~ 30% over z ~ 0.2–1.3, corresponding to lookback times of ~ 2.5–9 Gyr. The bars detected at z > 0.6 are primarily strong with ellipticities of 0.4–0.8. Remarkably, both the bar fraction and range of bar sizes observed at z > 0.6, appear to be comparable to the values measured in the local Universe for bars of corresponding strengths. Implications for bar evolution models are discussed.