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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...

We have observed three clusters at z∼ 0.7, of richness comparable to the low‐redshift sample of Butcher & Oemler (BO), and have determined their fraction of blue galaxies. When adopting the standard error definition, two clusters have a low blue fraction for their redshifts, whereas the fraction of the third one is compatible with the expected value. A detailed analysis of previous BO–like studies that adopted different definitions of the blue fraction shows that the modified definitions are affected by contaminating signals: colour segregation in clusters affects blue fractions derived in fixed metric apertures, differential evolution of early and late type spirals potentially affects blue fractions derived with a non‐standard choice of the colour cut, and the younger age of the universe at high redshift affects blue fractions computed with a colour cut taken relatively to a fixed non‐evolving colour. Adopting these definitions, we find largely varying blue fractions. This thorough analysis of the drawbacks of the different possible definitions of the blue fraction should allow future studies to perform measures in the same scale. Finally, if one adopts a more refined error analysis to deal with BO and our data, a constant blue fraction with redshift cannot be excluded, showing that the BO effect is still far from being detected beyond doubt.

In this series of papers we explore the evolution of late-type galaxies in the rich cluster Abell 85. In this first paper we revisit the complex dynamical state of A 85 by using independent methods. First, we analyze the galaxy redshift distribution towards A 85 in the whole range 0−40 000 km s −1 , and determine the mean redshifts of the background clusters A 87 and A 89, very close in projection to A 85. Then we search for substructures in A 85 by considering the 2D galaxy distribution of its members (13 000−20 000 km s −1 ) and by applying the kinematical 3D Δ-test to both projected positions and radial velocities. This clearly reveals several substructures: one close to the cluster core and three more projected towards the southeast, along the region where an X-ray filament has been extensively studied. We also analyse the distribution of the brightest blue galaxies across a major fraction of the cluster volume, considering if they are gas-rich or poor. We report a very asymmetric distribution of the blue member galaxies, with most of them to the east and southeast, namely in the region joining the core of A 85 to its farthest substructure in this direction -dubbed the SE clump. By matching our sample of bright blue member galaxies with H i detections reported in the literature, we identify gas-rich and gas-poor ones. As expected, the H i-rich blue galaxies follow the same trend as the parent sample, with most of them projected on the eastern side of the cluster as well. Interestingly no blue objects have been detected in H i up to a projected radius of 2 Mpc in this zone. We finally estimate the ram pressure stripping exerted by the intra-cluster medium as a function of the projected distance from A 85, in order to quantify how important this mechanism might be in sweeping the gas out of the infalling spirals.

Abstract. We present a catalogue of velocities for 551 galaxies (and give the coordinates of 39 stars misclassified as galaxies in our photometric plate catalogue) in a region covering about 100 × 100 (0.94×0.94 Mpc for an average redshift of 0.0555, assuming H 0 =50 km s −1 Mpc −1 ) in the direction of the rich cluster ABCG 85. This catalogue includes previously published redshifts by Beers et al. (1991) and Malumuth et al. (1992), together with our 367 new measurements. A total of 305 galaxies have velocities in the interval 13350−20000 km s −1 , and will be considered as members of the cluster. ABCG 85 therefore becomes one of the clusters with the highest number of measured redshifts; its optical properties are being investigated in a companion paper.Key words: galaxies: clusters: individual: ABCG 85; galaxies: distances and redshifts -instrumentation: spectrographs 1. Observations and data reduction Description of the observationsThe observations were performed with the ESO 3.6 m telescope equipped with MEFOS (see description below) during 6 nights on November 5-11, 1994 and 2 nights on November 24-26, 1995. The grating used with the Boller & Chivens spectrograph had 300 grooves/mm, giving a dispersion of 224Å/mm in the wavelength region Send offprint requests to: F. Durret, durret@iap.fr Based on observations collected at the European Southern Observatory, La Silla, Chile. Table 3 is also available in electronic form at CDS, Table 4 is only available in electronic form at CDS via anonymous ftp strasbg.fr/Abstract.html 3820−6100Å. The detector was CCD #32, with 512 2 pixels of 27 × 27 µm.The catalogue of galaxy positions used in this survey was obtained with the MAMA measuring machine and is presented in a companion paper ). This catalogue gives approximate magnitudes in the b J band, which were used to select the galaxies to be observed spectroscopically. CCD photometry of the central regions of the cluster in the V and R bands was later performed to recalibrate b J magnitudes and obtain V and R magnitudes for the entire photometric sample. We observed spectroscopically a total number of 21 fields, with exposure times of 2×20 minutes for the two fields with galaxies all brighter than b J = 18, and 2×30 minutes for the other ones. We obtained 519 spectra in total (plus the same number of sky spectra).

Context. Galaxies in clusters undergo several phenomena, such as RPS and tidal interactions, that can trigger or quench their star formation and, in some cases, lead to galaxies acquiring unusual shapes and long tails – some become jellyfish. Aims. We searched for jellyfish galaxy candidates in a sample of 40 clusters from the DAFT/FADA and CLASH surveys covering the redshift range 0.2 < z < 0.9. In MACS J0717.5+3745 (MACS0717), our large spatial coverage and abundant sampling of spectroscopic redshifts allowed us to pursue a detailed analysis of jellyfish galaxy candidates in this cluster and its extended filament. Methods. We retrieved galaxy spectroscopic redshifts in the NASA Extragalactic Database for galaxies in all the clusters of our sample (except for MACS0717 for which we had an extensive catalogue), looked at the Hubble Space Telescope ACS images of these objects (mainly the F606W and F814W bands), and classified them as a function of their likeliness to be jellyfish galaxies. We give catalogues of jellyfish galaxy candidates with positions, redshifts, magnitudes, and projected distance to their respective cluster centre. For MACS0717, an eight-magnitude optical and infrared catalogue covering the entire region allowed us to compute the best stellar population fits with LePhare through the GAZPAR interface. For the 31 jellyfish candidates in the other clusters belonging to the CLASH survey, we extracted up to 17 magnitudes available in the CLASH catalogues to fit their spectral energy distribution in the same way. Results. We found 81 jellyfish galaxy candidates in the extended region around MACS0717 as well as 97 in 22 other clusters. Jellyfish galaxy candidates in MACS0717 tend to avoid the densest regions of the cluster, while this does not appear to be the case in the other clusters. The best fit templates found by LePhare show that star formation is occurring. Stellar masses are in the range 109 − 1011 M⊙, and the star formation rates (SFRs) are in the 10−1 − 60 M⊙ yr−1 range for MACS0717 and in the 10−1 − 10 M⊙ yr−1 range for the other sample. Specific star formation rates (sSFRs) are notably higher in MACS0717, with more than half of the sample having values larger than 10−9 yr−1, while in the other clusters, most galaxies have sSFR < 10−10 yr−1. Stellar populations appear younger in MACS0717 (more than half have an age smaller than 1.5 × 109 yrs), and, following mid-infrared criteria, two galaxies may contain an active galactic nucleus. In a SFR versus stellar mass diagram, jellyfish galaxy candidates appear to have somewhat larger SFRs than “non-jellyfish star-forming” galaxies. For MACS0717, the mean sSFR of the 79 jellyfish galaxy candidates is 3.2 times larger than that of star-forming non-jellyfish galaxies (selected with log(sSFR)  ≥   − 11). Conclusions. Our jellyfish galaxy candidates are star-forming objects, with young ages and blue colours. Based on several arguments, the jellyfish candidates identified in MACS0717 seem to have fallen rather recently into the cluster. A very rough estimate of the proportions of jellyfish galaxies in the studied clusters is about 10%; this number does not seem to vary strongly with the cluster relaxation state, though this result must be confirmed with more data. Our sample of 97 galaxies in 22 clusters represents the basis of future works.

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