Subject headings: galaxies: individual (NGC 6503) — galaxies: kinematics and dynamics — galaxies: structure — methods: numerical 

## 1. Introduction 

The joint analysis of surface brightness profiles and rotation curves has traditionally yielded rich insights into the physics of disc galaxies. Surface brightness profiles allow for bulge-disc decomposition, while extended rotation curves constrain mass models (van Albada et al. 1985; Palunas & Williams 2000; de Blok et al. 2001; Kuzio de Naray et al. 2008). However, mass models are subject to degeneracies due, in part, to uncertainties in the mass-to-light ( M/L ) ratios of the baryonic components (e.g., Maller et al. 2000, Dutton et al. 2005). Breaking these degeneracies requires more data, such as a line of sight (LOS) velocity dis- persion profile or a colour profile. Additional data of this type allows for the creation of dy- namical models (Rix et al. 1997; Gebhardt et al. 2000; Widrow et al. 2003; Baes & Dejonghe 2004; Thomas et al. 2007). Dynamical models, in turn, provide the initial conditions for N − body simulations, which are needed to study the growth of bar and spiral instabili- ties. In addition, non-circular motions complicate the interpretation of gas rotation curves (Rhee et al. 2004; Valenzuela et al. 2007). Stellar rotation curve data may therefore help address these complications. A data set that includes surface brightness profiles, gas and stellar rotation curves and stellar velocity dispersions can provide constraints on fundamental galaxy parameters, along with information about stability to bar formation in the disc. 

Such a data set exists for the isolated dwarf Sc galaxy NGC 6503. Gas and stellar rotation curves were measured by de Vaucouleurs & Caulet (1982), Begeman (1987) and Bottema (1989) (hereafter B89); B89 also measured the stellar velocity dispersion profile and surface brightness profiles in the B − and R − bands. There are no strong asymmetries in galaxy structure (such as a bar), so it is a good candidate for analytic axisymmetric models. However, further investigation reveals several peculiarities. The galaxy possesses a sharp drop in velocity dispersion near the centre (known as a ‘ σ − drop’). The gas and stellar rotation curves are nearly coincident despite the standard asymmetric drift formula’s prediction that stars should noticeably lag behind the gas. Finally, the surface brightness profile displays four distinct regions: a central peak, a flat region indicating a Freeman (1970) Type II profile, an inner exponential of scale length ∼ 1 kpc and a shallower outer exponential. 

In this paper, we present several scenarios corresponding to differing interpretations of the data. For each scenario, we construct dynamical models that reproduce these features. We decompose the surface brightness using a S´ ersic bulge and an inner-truncated light profile 

