1. Introduction

The empirical correlation between the luminosity of spiral galaxies and their rotational velocity, named as "Tully-Fisher'' relation (TFR) (Tully & Fisher 1977), provides us with a method for estimating distances of galaxies on scales of cosmological interest. While its slope can be determined with high statistical significance using galaxies in several "well-behaved'' (without substructure) clusters, distributed with a large distance spread (0-10000 kms^-1) (Aaronson et al. 1986; Gavazzi et al. 1991), the determination of the zero-point relies on measurements of few nearby galaxies whose distances are accurately known by means of primary distance indicators.

In particular the parameters of the infrared H band (1.65m) TFR were derived by Aaronson et al. (1980) (hereafter AA80) using aperture photometry measurements of 12 nearby galaxies, several of which had the distance determined with the Cepheids method. A consistent calibration was obtained by Freedman 1990 who used 4 galaxies in common with AA80 (M 31, M 33, NGC 2403, M 81) adopting distance moduli redetermined with new data for Cepheids and the H aperture photometry of AA80.

Given the direct impact of the TFR zero-point on the determination of H₀, it is crucial to try to improve the IR photometry of the TF calibrators using the panoramic infrared detectors which recently became available in large format (256²). This method offers some obvious advantages over aperture photometry, allowing i) the determination of H_-0.5 with no growth-curve extrapolation and ii) accurate subtraction of unwanted contaminating stars in the field (see also Peletier & Willner 1993).

In this paper we present the first surface brightness near-infrared measurement of three TF calibrators in the NGC 2403-M 81 group: NGC 2403 itself, NGC 2366 and NGC 4236. H band measurements are checked against the aperture photometry of AA80. Meanwhile, given the growing importance in extragalactic studies of the new band filter (2.1m) (Wainscoat & Cowie 1992), which was designed to suppress part of the thermal background dominating the IR ground-based observations, we also obtained frames of the three galaxies with this filter.
We were able to photograph the large galaxies of this study, some of which span almost 20 arcmin in the sky, as a side-product of a project aimed at observing late-type Virgo Cluster galaxies (Boselli et al. 1997).