The structure of galactic disks: Studying late-type spiral galaxies using SDSS

Using imaging data from the SDSS survey, we present the g′ and r′ radial stellar light distribution of a complete sample of ∼90 face-on to intermediate inclined, nearby, late-type (Sb-Sdm) spiral galaxies. The surface brightness profiles are reliable (1σ uncertainty less than 0.2 mag) down to π ∼ 27 mag/□″. Only ∼10% of all galaxies have a normal/standard purely exponential disk down to our noise limit. The surface brightness distribution of the rest of the galaxies is better described as a broken exponential. About 60% of the galaxies have a break in the exponential profile between ∼1.5-4.5 times the scalelength followed by a downbending, steeper outer region. Another ∼30% shows also a clear break between ∼4.0-6.0 times the scalelength but followed by an upbending, shallower outer region. A few galaxies have even a more complex surface brightness distribution. The shape of the profiles correlates with Hubble type. Downbending breaks are more frequent in later Hubble types while the fraction of upbending breaks rises towards earlier types. No clear relation is found between the environment, as characterised by the number of neighbours, and the shape of the profiles of the galaxies. © ESO 2006.