Galaxy triplets in Sloan Digital Sky Survey Data Release 7-I. Catalogue

We present a new catalogue of galaxy triplets derived from the Sloan Digital Sky Survey (SDSS) Data Release 7. The identification of systems was performed considering galaxies brighter than Mr=-20.5 and imposing constraints over the projected distances, radial velocity differences of neighbouring galaxies and isolation. To improve the identification of triplets, we employed a data pixelization scheme, which allows us to handle large amounts of data as in the SDSS photometric survey. Using spectroscopic and photometric data in the redshift range 0.01 =z= 0.40, we obtain 5901 triplet candidates. We have used a mock catalogue to analyse the completeness and contamination of our methods. The results show a high level of completeness ( 80 per cent) and low contamination ( 5 per cent). By using photometric and spectroscopic data, we have also addressed the effects of fibre collisions in the spectroscopic sample. We have defined an isolation criterion considering the distance of the triplet brightest galaxy to the closest neighbour cluster, to describe a global environment, as well as the galaxies within a fixed aperture, around the triplet brightest galaxy, to measure the local environment. The final catalogue comprises 1092 isolated triplets of galaxies in the redshift range 0.01 =z= 0.40. Our results show that photometric redshifts provide very useful information, allowing us to complete the sample of nearby systems whose detection is affected by fibre collisions, as well as extending the detection of triplets to large distances, where spectroscopic redshifts are not available.

Consejo Nacional de Investigaciones Cientificas y Tecnicas de la Republica Argentina (CONICET)

Consejo Nacional de Investigaciones Cientificas y Tecnicas de la Republica Argentina (CONICET)

Secretaria de Ciencia y Tecnologia de la Universidad de Cordoba and Secretaria de Ciencia y Tecnica de la Universidad Nacional de San Jua

Secretaria de Ciencia y Tecnologia de la Universidad de Cordoba and Secretaria de Ciencia y Tecnica de la Universidad Nacional de San Jua

FAPESP

FAPESP

CNPq

CNPq

Alfred P. Sloan Foundation

Alfred P. Sloan Foundation

National Science Foundation

National Science Foundation

US Department of Energy

US Department of Energy

National Aeronautics and Space Administration

National Aeronautics and Space Administration

Japanese Monbukagakusho

Japanese Monbukagakusho

Max Planck Society

Max Planck Society

Higher Education Funding Council for England

Higher Education Funding Council for England