A photometric catalogue of the Coma cluster core

Abstract

Abstract. We have obtained a mosaic of CCD images of the Coma cluster in the V -band covering a region of approximately 0.4 degrees 2 around both central cluster galaxies NGC 4889 and NGC 4874. An additional frame of ∼ 90 arcmin 2 was taken of the south-west region around NGC 4839. We derived a catalogue of 7023 galaxies and 4096 stars containing positions, central surface brightnesses and isophotal V 26.5 magnitudes. We estimate that data is complete up to V 26.5 ∼ 22.5 and the surface brightness limiting detection value is µ ∼ 24 mag/arcsec 2 . In this paper we present the catalogue (available in electronic form alone 1 ), along with a detailed description of the steps concerning the data reduction and quality of the computed parameters.Key words: galaxies: clusters: individual: Comagalaxies: photometry -galaxies: luminosity function ObservationsWe have observed at the 3.6 m Canada-France-Hawaii Telescope during four nights in May 1993 with the MOS-SIS spectrograph (Le Fèvre et al. 1994) in the imaging mode. The Loral3 CCD, which has a 2048 × 2048 pixel format, provides images of 9.7 × 9.4 arcmin 2 (after discarding the vignetting area) -at the distance of the Coma cluster, 10 arcmin correspond to 0.4 h −1 50 Mpc -and the Send offprint requests to: C. Lobo, lobo@iap.fr Based on observations collected at the Canada-FranceHawaii telescope, operated by the National Research Council of Canada, the Centre National de la Recherche Scientifique of France, and the University of Hawaii. 1The catalogue is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html pixel size is 0.3145 arcsec. A "mosaic" of 21 overlapping images in the V -band was thus obtained covering a total field of about 0.4 degrees 2 centered on the two brightest central galaxies of Coma (NGC 4874 and NGC 4889). An additional frame was taken of the south-west NGC 4839 group. In Fig. 1 we display the observed regions. The exposure time for each image was 3 minutes. Flat-field frames of the twilight sky were also obtained with 1 second exposure time each, as well as a standard star calibration field in M 92 with a 90 second exposure. During the whole run the seeing (as estimated by the point spread function of stars in the images) varied from 0.9 to 1.4 arcsec. Flat-field, bias subtraction and correction of MOS distortionsAll the data reduction was performed with the IRAF package. Bias and flat-field corrections were made in the usual way. We used the twilight flat-field rather than a median flat produced from the images because the projected density and size of some of the bigger Coma galaxies did not allow to obtain a flat-field totally free of residuals. We applied the correction for distortion caused by the MOS camera optics (Le Fèvre et al. 1994) that mainly affects the corners of the CCD. This is done by running, for each image, the task GEOTRAN that corrects the distribution of the photon flux in the image pixels by means of a distortion map especially des...

Galaxy properties in clusters: dependence on the environment and the cluster identification techniques

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