EDP Sciences
Free access
Volume 391, Number 1, August III 2002
Page(s) 35 - 46
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20020377

A&A 391, 35-46 (2002)
DOI: 10.1051/0004-6361:20020377

Compact groups in the UZC galaxy sample

P. Focardi and B. Kelm

Dipartimento di Astronomia, Università di Bologna, via Ranzani 1, 40127 Bologna, Italy

(Received 15 May 2001 / Accepted 1 March 2002)

Applying an automatic neighbour search algorithm to the 3D UZC galaxy catalogue (Falco et al. 1999) we have identified 291 compact groups (CGs) with radial velocity between 1000 and 10 000 km s $^{\rm -1}$. The sample is analysed to investigate whether Triplets display kinematical and morphological characteristics similar to higher order CGs (Multiplets). It is found that Triplets constitute low velocity dispersion structures, have a gas-rich galaxy population and are typically retrieved in sparse environments. Conversely Multiplets show higher velocity dispersion, include few gas-rich members and are generally embedded structures. Evidence hence emerges indicating that Triplets and Multiplets, though sharing a common scale, correspond to different galaxy systems. Triplets are typically field structures whilst Multiplets are mainly subclumps (either temporarily projected or collapsing) within larger structures. Simulations show that selection effects can only partially account for differences, but significant contamination of Triplets by field galaxy interlopers could eventually induce the observed dependences on multiplicity.

Key words: galaxies: clusters: general -- galaxies: interactions

Offprint request: P. Focardi, Pfocardi@bo.astro.it

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