1 Introduction

Rich galaxy clusters represent the largest bound masses in the present-day Universe. Differences in the properties of clusters, such as shape, substructure, galaxy concentration and galaxy population are generally thought to reflect different evolutionary stages. Hence, their investigation is important for the understanding of the formation and evolution of large aggregates in the Universe.

A426 (Perseus) is a nearby rich galaxy cluster of Bautz-Morgan class II-III (Bautz & Morgan [1970]) and Rood-Sastry type L (Struble & Rood [1987]). It has been recognised long ago that this cluster is remarkable in several aspects: it shows one of the highest velocity dispersion among the nearby clusters, a prominent chain of bright galaxies in the core, and an exceptionally strong deficiency of spiral galaxies (Chincarini & Rood [1971]; Melnick & Sargent [1977]; Kent & Sargent [1983]). Recent studies, however, find a higher fraction of spirals (Andreon [1994]). A426 is one of the brightest clusters observed in the X-ray waveband with a massive cooling flow in its centre (Mushotsky et al. [1978]; Allen et al. [1992]; Allen & Fabian [1997]; Peres et al. [1998]). X-ray emission has been observed up to more than one degree from the cluster core (Nulsen & Fabian [1980]; Ulmer et al. [1980]; Ettori et al. [1998]). The X-ray centre is not identical with the centre of the optical galaxy positions (Branduardi-Raymont et al. [1981]; Snyder et al. [1990]; Ulmer et al. [1992]) which has been interpreted as a signature of a cluster merger (Ulmer et al. [1992]). Significant substructure in the X-ray image has been discussed as evidence that the cluster is not in a relaxed state and is consistent with a recent merger (Schwarz et al. [1992]; Mohr et al. [1993]; Ettori et al. [1998]). Clear evidence for substructure in the optical galaxy distribution has been reported in several studies (Baier [1979], [1984]; Escalara et al. [1994], Andreon [1994]) whereas others did not find strong substructure (Geller & Beers [1982]; Fitchett & Webster [1987]; Dressler & Shectman [1988]) or no substructure at all (Bird [1994]). The Perseus cluster hosts several galaxies with active nuclei, pronounced radio structures, enhanced far-infrared emission, and/or signs of strong gravitational interactions.

The complex innermost central region of the cluster including the remarkable central dominant galaxy NGC1275 has been the subject of various detailed studies. NGC1275 hosts an active nucleus with spectral and radio properties intermediate between a Seyfert galaxy and a BL Lac object (Ferruit & Pécontal [1994]; Véron [1978]). The nucleus is associated with the FRI radio source PerA which has been intensively studied on different scales (e.g. Ryle & Windram [1968]; Pedlar et al. [1990]; Vermeulen et al. [1994]). The lobes of PerA are interacting with the X-ray emitting intra-cluster plasma, and their structure may be explained as due to an oscillating motion of the cD galaxy NGC1275 in the cluster potential (Böhringer et al. [1993]). The radio lobes are embedded within a radio halo which has been traced out to a diameter of 300kpc (Pedlar et al. [1990]; Burns et al. [1992]). NGC1275 is surrounded by an extended system of optical emission-line filaments with a complex velocity structure (Minkowski [1957]; Burbidge & Burbidge [1965]; Rubin et al. [1977]; Kent & Sargent [1979]; Caulet et al. [1992]; Ferruit et al. [1997]). The low velocity filament system has been related either to the cooling flow (Fabian & Nulsen [1977]; Fabian [1994]; McNamara et al. [1996]; Dixon et al. [1996]) or to the occurrence of a recent merger which was also suggested to explain the origin of the system of young globular clusters (Holtzman et al. [1992]).

Due to its proximity and its richness, A426 is well suited for the investigation of several aspects of the structure of galaxy clusters and statistical properties of cluster galaxies, such as luminosity and morphological segregation or luminosity functions. On the other hand, however, such studies are hampered by the low Galactic latitude of the field (the Perseus cluster is located at $l=150\hbox{$.\!\!^\circ$}6, b=-13\hbox{$.\!\!^\circ$}3$)and, consequently, by the high density of Galactic foreground stars as well as increased, and perhaps irregular, foreground extinction. This may be one reason why the optical data base for the galaxies in A426 is relatively poor compared with other nearby clusters. (For instance, for the Coma cluster Doi et al. ([1995]) presented homogeneous photometric data and morphology for 450 galaxies, and the "Virgo photometry catalogue'' (Young & Currie [1998]) contains 1180 galaxies.) Chincarini & Rood ([1971]) based their study of the dynamics of A426 on 47 galaxies. Melnick & Sargent ([1977]) classified 175 galaxies brighter than $m_{\rm pg} \approx 16$ in a region of about $100\hbox{$^\prime$}$ from the cluster centre on a Palomar IIIa-J Schmidt plate. They found an exceptionally small number of spirals (7%) with a flat radial distribution to be compared with a steep radial distribution for S0s and Es. Bucknell et al. ([1979]) presented photographic photometry for 233 galaxies with V₂₅ < 17.5 in the inner region of A426 within a cluster-centric radius of $\approx 30\hbox{$^\prime$}$. Galaxies of this "BGP sample'' were combined by Kent & Sargent ([1983], hereafter KS83) with a near-complete sample of galaxies brighter than $m_{\rm pg} \approx 15.7$within a radius of $3^\circ$ from NGC1275 taken from the Catalogue of Galaxies and Clusters of Galaxies (Zwicky & Kowal [1968]), hereafter called "Zwicky sample''. A combined sample of 190 galaxies was used by KS83 for their study of the dynamics of the Perseus cluster.

Morphological types, estimated from a Palomar Schmidt plate, have been available only for a small fraction of the galaxies from the KS83 sample. Significantly refined morphological information were derived by Poulain et al. ([1992]) for 91 early-type galaxies of this list from a detailed isophotal shape analysis. Thanks to the high resolution of their CCD images, a variety of fine details in the structure of the galaxy images could be uncovered. These results have demonstrated the sensitivity of recognising the morphological types for rather remote galaxies on the detectability of fine structure details, i.e. on the signal-to-noise ratio and spatial resolution. In particular, the revision of the morphological types has drastically decreased the estimated percentage of Es and S0s by a factor of more than two. Andreon ([1994]) studied morphological segregations in A426 from a BGP subsample of 96 galaxies with $B\le 15.7$ in the inner $\sim$30' region. He took the morphological type information from Poulain et al. ([1992]) for most galaxies and from a visual inspection of Schmidt plates taken at Palomar and Calern, respectively, in the remaining cases. Andreon et al. ([1997a]) extended the isophotal analysis and provided morphological data for a complete sample of galaxies with $m_{\rm Zwicky} < 15.7$ in a region of $5\hbox{$.\!\!^\circ$}3\times 5\hbox{$.\!\!^\circ$}27$. De Propris & Pritchet ([1998]) presented a study of the faint end of the galaxy luminosity function from a deep $14'\times14'$ image of the cluster centre taken with the 3.6m CFHT in the I-band.

The main aim of the present paper is to contribute to an extended data base for the galaxies in a large field of the Perseus cluster. We provide a new catalogue of 660 galaxies in a field of nearly 10 square degrees containing accurate positions (important for cross-identifications), photometric data and morphological information. Two thirds of the galaxies are published for the first time. The study is based on digitised Schmidt plates taken with the Tautenburg 2m telescope. Schmidt plates still provide an important tool for the investigation of clusters with extentions as large as for A426. The disadvantage of a lower limiting magnitude, as compared with deep CCD images, can be widely reduced by the digital co-addition of a large number of plates. Due to the gain in the signal-to-noise ratio, stacking of Schmidt plates provides a powerful method for the evaluation of faint, extended structure details. Preliminary results from this study have been discussed in Brunzendorf & Meusinger ([1996]).

The observational material used for the present study is described in the next Section. The digitisation of the Schmidt plates by means of the Tautenburg plate scanner is outlined in Sect.3, followed by a description of the procedures for obtaining galaxy positions, photometric information, and some radial velocities in Sect.4. Section5 deals with the evaluation of morphological properties. The structure of the galaxy catalogue is briefly described in Sect.6. Finally, the catalogue data are used in Sect.7 to demonstrate several statistical properties of the galaxies in A426: the projected distributions of morphological types, the position of the cluster centre, morphological segregation, the distribution of the galaxy position angles, the B-band luminosity function, and the total B-luminosity of the cluster. Conclusions are given in Sect.8. The catalogue of galaxies in A426 is only available in electronic form at the CDS.

Throughout this paper we assume a redshift of z = 0.0183 (Abell et al. [1989]) for the Perseus cluster. Angular separations can be converted into linear distances by $1' \equiv 31.5\,h_{50}^{-1}$kpc.