Catarina Lobo

Extending the Butcher–Oemler effect up to z∼ 0.7

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.

Galaxy evolution in Abell 85: I. Cluster substructure and environmental effects on the blue galaxy population

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 )a nd 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.

A photometric catalogue of the Coma cluster core

We have obtained a mosaic of CCD images of the Coma cluster in the V-band covering a region of approximately 0.4 degrees

A PHOTOMETRIC CATALOGUE OF GALAXIES IN THE CLUSTER ABELL 85

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Bulgeless Galaxies at Intermediate Redshift: Sample Selection, Color Properties, and the Existence of Powerful Active Galactic Nuclei

around both central cluster galaxies NGC 4889 and NGC 4874. An additional frame of

Red bulgeless galaxies in SDSS DR7. Are there any AGN hosts

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The intermediate-redshift galaxy cluster CL 0048-2942. Stellar populations.

90 arcmin

A Multiple Dry Merger at z = 0.18: Witnessing The Assembly of a Massive Elliptical Galaxy

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AGN Feedback and Quenching of Star Formation: A Multiwavelength Approach with the EURO-VO

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

A catalogue of velocities in the cluster of galaxies Abell 85

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