A 2.2 Micron Catalogue of Stars in NGC 3603

Abstract

We present a photometric catalogue of ∼11,500 stellar objects identified in the field of the Galactic starburst cluster NGC 3603. The catalogue is based on high quality Ks-band data obtained at the Very Large Telescope (VLT). We extract from the catalogue the Ks-band luminosity function and evaluate the underlying IMF. We do not find any evidence for a lower mass cut-off down to approximately 0.5M . The slope of the Ks-band luminosity function is consistent with a Miller-Scalo type IMF. 1. Observations and photometry Near-infrared images at Ks-band (2.16μm) have been taken of the Galactic starburst cluster NGC 3603 and its southern surrounding, using the ISAAC instrument at the VLT. The atmospheric conditions during the observations were very good, resulting in an image quality of 0.4′′ − 0.6′′ FWHM on pointsources. The telescope was offset to several different positions in order to cover a total field of 3.3′ × 6.5′ (see Nurnberger & Petr-Gotzens 2002, for an outline of the surveyed field). After standard data reduction, photometry was performed on 20 selected (best quality), individual ISAAC images. PSF-photometry using DAOPHOT under IRAF was applied, since severe stellar crowding in the NGC 3603 cluster makes aperture photometry less reliable. Comparing the results of PSFphotometry to our aperture photometry, carried out on a stacked mosaic and presented in Nurnberger & Petr-Gotzens (2002), shows a decrease in the mean photometric error for cluster stars by ∼ 3%. Absolute photometric calibration was achieved by calculating the nightly zero point from observations of two different standard stars, taken just before, in between and just after our observations of NGC 3603.