The statistical properties of the Tully-Fisher relation (TFr), like its scatter and slope, and in more detail the characteristics of dark matter halos around galaxies, like their core densities and radii, are of great interest to those who study galaxy formation scenarios. The relevant observables for the TFr are total luminosities and rotational velocities while actual rotation curves and luminosity profiles are required to obtain constraints on the density profiles of dark matter halos. However, the available data sets from which these observables can be obtained are often suffering from incompleteness, distance uncertainties and inhomogeneous observing and data analysis techniques.
Furthermore, the interpretation of the observables is not always unambiguous. For instance, the rotational velocity of a galaxy is generally inferred from the width of its global HI profile and often this measured width is being related directly to the dark matter potential (e.g. Navarro & Steinmetz 2000). However, the width of the HI profile is a complicated convolution of the 2-dimensional distribution of HI in a galaxy disk and the shape and extent of its rotation curve as sampled by the HI gas. Needless to say one has to exercise caution when relating the observed scatter and slope in the TFr to the outcome of numerical and semi-analytical simulations of galaxy formation. This is especially the case when the observed TFr was constructed to serve as an empirical distance estimator and the selection criteria and applied corrections to the raw observables were optimized to linearize the relation and minimize its scatter.
To overcome some of the observational issues, we initiated a program to obtain detailed multi-band photometric and kinematic information on individual galaxies in a well-defined, complete sample. The nearby Ursa Major cluster of galaxies provides a particularly suitable sample. In the first place, the galaxies in the cluster are all at roughly the same distance. Therefore, there is little doubt about their relative luminosities, sizes and masses. Furthermore, the Ursa Major cluster contains overwhelmingly gas-rich systems and the morphological mix of its galaxy members is close to that of the lower density field. A detailed discussion on the definition of the Ursa Major cluster is given by Tully et al. (1996) (Paper I). The characteristics of this cluster will be discussed in more detail in Sect. 2.
In this paper we present the results of an extensive 21 cm-line synthesis
imaging survey of individual galaxies in the Ursa Major cluster using
the Westerbork Synthesis Radio Telescope (WSRT). The HI data are
presented in the form of an atlas. Multi-band optical and near-infrared
imaging photometry is presented in Paper I together with B-band and
-band images of all identified cluster members. Forthcoming
papers in this series will use these data to investigate the TFr while
the HI rotation curves will be supplemented in the inner regions with
already obtained high resolution optical rotation curves to derive
constraints on the structural properties of the dark matter halos and
the mass-to-light ratios of the stellar populations.
This data paper is organized as follows. Section 2 describes the Ursa
Major cluster in more detail and contains morphological and photometric
information on the galaxies observed with the WSRT. Data acquisition and
reduction procedures are explained in Sect. 3. Section 4 explains how
the corrected linewidth can be matched to 
and
from the rotation curves through an
appropriate correction for turbulent motion. Inclinations are derived
from the optical images, HI column density maps and HI velocity fields
and Sect. 5 presents a comparison of these inclinations. The layout of
the HI atlas is described in Sect. 6 with details about the various
elements of the atlas pages. The HI properties of the Ursa Major cluster
galaxies as a sample are presented in Sect. 7. Some concluding remarks
are given in Sect. 8.
Copyright ESO 2001