Astron. Astrophys. 327, 562-568 (1997)

1. Introduction

NGC 1427A is the brightest irregular galaxy in the Fornax cluster. It is about 3 magnitudes brighter than other Fornax galaxies that are classified as irregulars (Ferguson 1989). Its total B magnitude is mag (de Vaucouleurs et al. 1991). Assuming a distance of 16.4 Mpc (Kohle et al. 1996) to the Fornax cluster, the apparent B magnitude corresponds to an absolute magnitude of mag, which is nearly identical to the LMC luminosity mag, (de Vaucouleurs et al. 1991), assuming a LMC distance modulus of mag. The linear dimension of NGC 1427A is about 11 kpc in major axis ( within the isophote at mag/arcsec²), slightly larger than the LMC which has a major axis diameter of kpc. Table 1 summarizes some properties of NGC 1427A compared with the LMC. The values are from the Third Reference Catalogue of Bright Galaxies (de Vaucouleurs et al. 1991), if no other reference is given.

Table 1. Some properties of NGC 1427A and of the LMC

The projected distance to the central Fornax galaxy NGC 1399 is , about 109 kpc at the cluster distance. Since NGC 1399 has an extended cD halo of about 500 kpc diameter (Schombert 1986, Killeen & Bicknell 1988), one might expect tidal interaction of both galaxies. However, the radial velocities, measured in HI (Bureau et al. 1996), of NGC 1427A () and NGC 1399 () differ by about which is nearly twice the cluster velocity dispersion (, Ferguson & Sandage 1990). NGC 1427A rather agrees with the velocity of NGC 1404 (). NGC 1404 is nearly as luminous as NGC 1399 and has a projected distance to NGC 1427A of about 75 kpc.

In this paper we discuss the similarity of the morphological properties of NGC 1427A and the LMC, as well as the stellar content, such as OB associations and young clusters, X-ray properties and the evolutionary state.

The organization of the paper is as follows: In Sect. 2 we describe observation and reduction of the data, Sect. 3 deals with the large scale light distribution of NGC 1427A, Sect. 4 discusses the colors and H properties of the resolved sources, Sect. 5 discusses the properties of the cluster candidates. Sect. 6 gives a short discussion of the X-ray informations and in Sect. 7 we summarize our results.

© European Southern Observatory (ESO) 1997

Online publication: April 6, 1998
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