Bar evolution over the last 8 billion years: A constant fraction of strong bars in th GEMS Survey

One-third of present-day spirals host optically visible strong bars that drive their dynamical evolution. However, the fundamental question of how bars evolve over cosmological times has yet to be resolved, and even the frequency of bars at intermediate redshifts remains controversial. We investigate the frequency of bars out to z ~ 1 drawing on a sample of 1590 galaxies from the Galaxy Evolution from Morphologies and SEDs survey, which provides morphologies from Hubble Space Telescope Advanced Camera for Surveys (ACS) two-band images and accurate redshifts from the COMBO-17 survey. We identify spiral galaxies using three independent techniques based on the Sersic index, concentration parameter, and rest-frame color. We characterize bar and disk features by fitting ellipses to F606W and F850LP images, using the two bands to minimize shifts in the rest-frame bandpass. We exclude highly inclined (i > 60degrees) galaxies to ensure reliable morphological classifications and apply different completeness cuts of M ≤ -19.3 and -20.6. More than 40% of the bars that we detect have semimajor axes a 0.7. Our findings of a large and similar bar fraction at these three epochs favor scenarios in which cold gravitationally unstable disks are already in place by z ~ 1 and where on average bars have a long lifetime (well in excess of 2 Gyr). The distributions of structural bar properties in the two slices are, however, not statistically identical and therefore allow for the possibility that the bar strengths and sizes may evolve over time

Observations of the High Redshift Universe

(Abridged) In these lectures aimed for non-specialists, I review progress in understanding how galaxies form and evolve. Both the star formation history and assembly of stellar mass can be empirically traced from redshifts z~6 to the present, but how the various distant populations inter-relate and how stellar assembly is regulated by feedback and environmental processes remains unclear. I also discuss how these studies are being extended to locate and characterize the earlier sources beyond z~6. Did early star-forming galaxies contribute significantly to the reionization process and over what period did this occur? Neither theory nor observations are well-developed in this frontier topic but the first results presented here provide important guidance on how we will use more powerful future facilities.Comment: To appear in `First Light in Universe', Saas-Fee Advanced Course 36, Swiss Soc. Astrophys. Astron. in press. 115 pages, 64 figures (see http://www.astro.caltech.edu/~rse/saas-fee.pdf for hi-res figs.) For lecture ppt files see http://obswww.unige.ch/saas-fee/preannouncement/course_pres/overview_f.htm