1 Introduction

A polar-ring galaxy (hereafter referred to as PRG) consists of a flattened galaxy with an outer ring of gas, dust, and stars rotating in a plane approximately perpendicular to the central disc. Kinematically confirmed PRGs with a disc-dominated central galaxy tend to have wide, extended polar rings, while bulge-dominated objects show only short, narrow rings (Reshetnikov & Sotnikova 1997; Whitmore 1991). The PRGs probably represent merger products, and their study may give us valuable clues about the process and frequency of merging; their visible environment appears to be similar to that of normal galaxies (Brocca et al. 1997), which may support long formation and evolution times of the rings. In addition, measurement of rotation in the two nearly perpendicular planes of the ring and galaxy provide one of the few available probes of the three-dimensional shape of galactic gravitational potentials, and hence the shape of dark and luminous matter distributions.

The PRG catalogue of Whitmore et al. (1990, hereafter PRC) provides us with over a hundred known polar-ring galaxies and PRG candidates, as well as list of possibly related systems, divided into four main categories (number of objects per category from PRC):

1.

A: Kinematically-determined Polar-Ring Galaxies (9 objects);

2.

B: Good Candidates for Polar-Ring Galaxies (24 objects);

3.

C: Possible Candidates for Polar-Ring Galaxies (73 objects);

4.

D: Systems Possibly Related to Polar-Ring Galaxies (51 objects).

Since the publication of the PRC, 4 category B and 4 category C objects have been promoted to category A (B-03 = IC 1689, B-17 = UGC 9562, B-19 = AM 2020-504, B-21 = ESO603-G21, C-13 = NGC 660, C-24 = UGC 4261, C-27 = UGC 4385 and C-45 = NGC 5128; see Reshetnikov & Combes 1994; Reshetnikov & Sotnikova 1997; van Driel et al. 1995), all of which are included in our survey and will be considered members of the A category in this paper.

The scientific goals of our 21-cm H I line surveys of PRGs, presented here and in a previous paper (Richter et al. 1994, Paper I) are to:

1.

Establish redshifts for the objects with previously unknown redshift;

2.

Measure the amount of neutral hydrogen in these systems and examine its correlations with other observational parameters;

3.

Identify objects for subsequent synthesis mapping; H I maps together with optical line studies will show which of the new morphological candidates are true polar-ring galaxies, and high-resolution maps will allow dynamical modelling.

Detailed observations of PRGs in the 21-cm H I line with large radio synthesis telescopes like the Australia Telescope, VLA or Westerbork, are crucial for an understanding of the dynamical state of these systems (see, e.g., Schechter et al. 1984; van Gorkom et al. 1989; Cox 1996; Arnaboldi et al. 1997; and the Catalogue of H I maps by Martin 1998). Such mapping measures the distribution and the velocity field of gas in the rings, both of which are required for accurate determination of the shape of the dark halo. Together with optical absorption-line studies of the central galaxy, rotation in the ring gas determines whether morphological candidates are true polar rings. Further, knowledge of the ring mass is necessary to assess the stability of the rings against differential precession, an important consideration in estimating the time since its formation.

Thus, the main purpose of the single-dish H I line surveys of PRGs presented here and in two previous papers is to enlarge the sample of polar-ring systems with sufficient H I gas to allow high-resolution synthesis mapping. After having first observed a sample of 47 PRGs in the 21-cm H I line with the 140-foot (43-m) Green Bank telescope (Paper I), and a sample of 44 with the 100-m Effelsberg telescope (Huchtmeier 1996, Paper II), we now present observations of a similar sample of 50 PRGs with the 94-m diameter equivalent Nançay decimetric radio telescope and of 3 objects observed with the 64-m Parkes dish. An analysis of all available H I data on PRGs and related objects will be presented in the next paper in these series (van Driel et al., in preparation).

In Sect. 2 the sample of PRGs observed in Nançay is presented. In Sect. 3 the results of the Nançay H I observations are shown and compared to H I line observations made elsewhere, either for our PRG survey or for other studies.