The structure and metallicity gradient in the extreme outer disk of NGC7793

Abstract

Studies of outer regions of spirals disks are fundamental to our understanding of both the process of galaxy assembly and the subsequent secular evolution of galaxies. In an earlier series of papers, we explored the extent and abundance gradient in the outer disk of NGC300 and found an extended purely exponential disk with a metallicity gradient which flattens off in the outermost regions. We now continue the study of outskirts of pure disk spirals with another Sculptor Group spiral, NGC7793. Using the Gemini Multi Object Spectrograph camera at Gemini South, we trace the disk of NGC7793 with star counts out to ∼9 scale lengths, corresponding to 11.5kpc at our calibrated distance of 3.61 ± 0.53Mpc. The outer disk of NGC7793 shows no evidence of a break in its light profile down to an effective surface brightness of ∼30 mag arcsec-2 (∼3 mag arcsec-2 deeper than what has been achieved with surface photometry) and exhibits a non-negative abundance gradient within the radial extent of our data.