2 Sample

2.1 Sample selection  

The sample objects were selected from the catalogued disk galaxies in the Pisces-Perseus supercluster area, $22^{\rm h}<{\rm RA}<4^{\rm h}$ and $0^\circ<\delta<45^\circ$, excluding obvious foreground members with $V_{\rm H}<3000\,$kms^-1$\,$and ellipticals. To best fit the camera fields of view to be employed, the sample was restricted to galaxies with optical major axis $0\hbox{$.\mkern-4mu^\prime$}5<a<4\hbox{$.\mkern-4mu^\prime$}0$, and, among these, we further selected those with available good-quality 21-cm spectra (Giovanelli & Haynes 1989 and references therein). These selection criteria result into about 950 galaxies, mainly late spirals. From this set two distinct subsamples were extracted. Sample A comprises about 150 galaxies, randomly selected to cover the entire area and inclination range, and with types Sb or later; for these objects only H-band data were acquired. Sample B includes the 50 cluster galaxies with distance $d_{\rm c} < 5 \hbox{$.\!\!^\circ$}5$ from the Pisces cluster center ($1^{\rm h} 20^{\rm m}, 33^\circ$), with optical size $D_{25} \geq 0\hbox{$.\mkern-4mu^\prime$}8$,and inclination $30^\circ < i < 75^\circ$;for these objects, ranging in morphology from S0 to Sd, J, H, and K-band images were acquired.

Due to malfunctions and bad weather, not all the sample objects could be observed. As a whole 177 objects were observed at least in one band (usually H), 147 of which belong to the supercluster sample (sample A) and 35 to the cluster one (sample B); five galaxies are common to both samples. This paper presents data for the 174 galaxies imaged in the H bandpass.

2.2 Sample statistics

The spatial distribution of the sample objects is depicted, in an equal-area projection, in Fig. 1. The region is bounded to the east by the Zone of Avoidance due to extinction in the Galactic plane. Despite its scarcity, our sample delineates the overall structure of the supercluster as portrayed by much richer sets (e.g. Giovanelli et al. 1986). The main ridge appears clearly, spanning the entire RA range between 30$^\circ$and 40$^\circ$ declination, as well as the southern extensions down to the A400 and Pegasus clusters. Despite the presence of several rich clusters in the area, the only clear clustering is noted at the position of the Pisces cluster (NGC 507: $1^{\rm h} 20^{\rm m}, \, \, \, 33^\circ$); obviously this is due to the galaxies of sample B.

  

Figure 1: Position of the sample objects in equatorial coordinates. In this equal-area projection, the clustering at $1^{\rm h} 20^{\rm m}$ and $33^\circ$ coincides with the Pisces cluster (sample B)

In Fig. 2 we plot the cumulative distribution in photographic magnitude ($B_{\rm T}$ system). When compared to the expectation for a uniformly distributed set, the sample starts deviating and losing completeness at $\sim$14 B-mag; there is also a notable a lack of bright galaxies (m_B < 13.0). Both limits are mainly induced by the constraints on the apparent size and only to a minor degree by the characteristics of the UGC (Nilson 1973) and CGCG (Zwicky et al. 1961-68) catalogues, from which the sample was originally drawn; the scarcity of bright objects also follows the exclusion of foreground objects.

  

Figure 2: Number of galaxies with apparent magnitude brighter than mB vs. mB ($B_{\rm T}$ system). Error bars are $1\sigma$ uncertainties due to counting statistics. The dotted line, shown for comparison, has the slope 0.6 expected for a uniform distribution in euclidean space; the position of the line is arbitrary

The morphological distribution is illustrated in Fig. 3. The types are drawn from the RC3 catalogue (de Vaucouleurs et al. 1991) where most of our sample galaxies have a detailed Revised Hubble (RH) classification; only 16 are classified S or SB without further specification, and only two non-UGC objects are not classified. As expected, due to the selection based on 21-cm observations, the sample mainly consists of late spiral types and peaks around T=4, that is Sbc.

  

Figure 3: Morphological distribution of the sample galaxies. N is the number of objects per RH classification bin, T is the index of stage along the Hubble sequence from the RC3. Spiral types are also reported on top of each bin. The rightmost bin, coded S, refers to objects classified S or SB without further specification