Disk morphology of NGC 628 from large field CCD UBVRI photometry.

The authors present results on the surface photometry of the spiral galaxy NGC 628, obtained using the Istituto di Astrofisica Spaziale CCD camera at the 60/90/180 cm Schmidt telescope of the Osservatorio Astronomico di Roma at Campo Imperatore. The large field of view of that unusual combination allows to collect single frame images of (25×17) arcmin² of this large angular diameter object. The analysis of the UBVRI profiles extracted by a dedicated software using a median algorithm, shows a variation in disk scale length vs. wavelength, and a radial B-V trend consistent with the Larson and Tinsley model. The study highlights two main regions in this galaxy: the inner disk and the outer disk, dominated by two different stellar populations. Moreover, correlating the U-B, B-V diagram of circular subsets of the galaxy, to the Larson and Tinsley model, the authors derive an estimation of the star formation rate in different radial parts of this object.