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

Abstract

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.

An isolated compact galaxy triplet

“…O'Mill et al (2012) constructed a catalogue of triplets with their primary galaxies (M r < −20.5) selected from a volume-limited sample in the Sloan Digital Sky Survey Data Release 7 (SDSS-DR7) Abazajian et al (2009) (hereafter O-sample). This catalogue comprises 1092 triplets with redshift range 0.01 ≤ z ≤ 0.14.…”

Galaxy triplets in Sloan Digital Sky Survey Data Release 7 – III. Analysis of configuration and dynamics

“…In O'Mill et al (2012) (hereafter paper I) we present a method to identify triplets of galaxies in the Seventh Data Release of the Sloan Digital Sky Survey. In Duplancic et al (2013) (hereafter paper II) we analyse the properties of galaxies in a sample of isolated triplets of bright galaxies and found that these systems could be considered as an analogous of compact groups with a lower number of members.…”

Dissecting galaxy triplets in the Sloan Digital Sky Survey Data Release 10 – I. Stellar populations and emission line analysis

“…In this work, we have used the algorithm described in O'Mill et al (2012) to identify isolated galaxy triplets in a volumelimited sample (Mr < −20.5 + 5 log h70) from the Sloan Digital Sky Survey Data Release 10. An initial sample of 97 galaxy systems between 0.04 z 0.1 is compiled.…”

“…We have obtained a sample of galaxy triplet candidates in the volume-limited sample described in the previous section with the algorithm developed by O'Mill et al (2012).…”

“…Recently, O'Mill et al (2012) have compiled a catalogue of triplets of galaxies from the Sloan Digital Sky Survey Data Release 7 (SDSS-DR7, Abazajian et al 2007), providing a spectroscopic and photometric sample of triplet system candidates. Further analysis carried out by Duplancic et al (2013), based on photometric colours and star formation activity, indicates that galaxy triplets present similar properties to compact groups and that these systems, comprising luminous galaxies, are actually an extension of compact galaxy groups with a smaller number of members.…”