1 Introduction

Our present knowledge of the near-infrared properties of galaxies is still very sketchy, because panoramic astronomical imaging receivers in that domain have only been available recently. For samples complete in the near-infrared band, properties such as galaxian colors and sizes in the near-infrared and their dependence on morphological type are almost unknown. And so are the deep near-infrared luminosity functions of galaxies in the field and in clusters. The former have been investigated by Gardner et al. (1997) and, for an optically-selected sample, by Szokoly et al. (1998), but they cover just its bright end. The latter concern the bright end of intermediate-distance clusters (Trentham & Mobasher 1998; Barger et al. 1996); an exception is the study of the luminosity function of the center of Coma by de Propris et al. (1998), which reaches $H\sim 16$ mag (at 80% completeness).

Figure 1: H-band mosaic of the region under investigation. Faint objects have $H\sim 16$ in this heavly rebinned and compressed (for display purposis) image. The field is $\sim 20 \times 24$ arcmin. North is up and East is left. The two dominant galaxies of the Coma cluster are located near the South-West corner

Near-infrared properties of galaxies are very useful for a number of projects. These quantities allow the determination of a possible change with redshift in the galaxy properties, such as the "downsizing" suggested by Cowie et al. (1996). The passband dependence, from the optical to the near-infrared, of the tilt of the fundamental plane gives a clear indication of whether this tilt is due to a variation of metallicity, age or a breakdown in homology along the early-type sequence (Pahre et al. 1998), but the fundamental plane in the near-infrared is only beginning to be studied. The existence of dwarf galaxies with blue B-K colors has been assumed, in order to explain galaxy counts in B and K (Saracco et al. 1996), but their density in the universe still has to be measured.

Near-infrared measurement of nearby galaxies and clusters are valuable, because even at high redshift the near-infrared falls into a well known part of the restframe spectrum, at the difference of the optical window, which, at high redshift, samples the almost unexplored restframe ultraviolet emission. In passing, the galaxy size distribution plays a fundamental role in performing new cosmological tests (Petrosian 1998). Their determination in the present Universe is critical for these tests.

In short, good reference samples of galaxies with well established spectrophotometric properties - from the optical to the near-infrared - are urgently needed for the study of galaxy properties and their evolution.

We thus started a program to establish the near-infrared photometric properties of galaxies in Coma, the archetypical zero-redshift cluster, for which a large amount of reliable data (photometry and morphological types) are already available. We adopted the H band because it corresponds to the K band - still observable from the ground - for galaxies at intermediate redshift ( $z \sim 0.3$), thus allowing a direct comparison of the galaxy properties over a redshift range where evolution in clusters has been detected (Butcher & Oemler 1984). J-band ($1.2 \mu$) images for the same region have been already acquired and their reduction is in progress.

Figure 2: Exposure map for the whole imaged field ( $20\times 24$ arcmin wide). North is up and East is left. Darker regions were exposed longer. Exposure times range from 450 s (dark regions), to 0 (white regions). Mean exposure times are, from left to right, 400, 100 and 310 s

Figure 3: Magnitude zero point, as measured from standard stars (solid dots) and from Coma cluster galaxies (crosses), splitted by date and then sorted by an arbitrary sequential order. Note that one tickmark along the ordinates is 0.05 mag. Error bars for galaxies account for centering error and published errors of the standard (statistical errors are virtually null for our measure of theses bright objects observed for the photometric calibration), whereas for stars they are the ratio of the interquartile range of the various measures by the square root of the number of measures. Labels correspond to names: from Dressler (1980) for galaxies and from Casali & Hawarden (1992) for stars