2MASS galaxies in the Fornax cluster spectroscopic survey^*

¹ Astrophysics Group, Department of Physics, University of Bristol, Bristol BS8 1TL, UK e-mail: R.Morris@bristol.ac.uk
² Astronomy Unit, School of Mathematical Sciences, Queen Mary University of London, Mile End Road, London E1 4NS, UK
³ Department of Physics, University of Queensland, QLD 4072, Australia
⁴ Department of Physics, University of California Davis, CA 95616, USA
⁵ Institute for Geophysics and Planetary Physics, Lawrence Livermore National Laboratory, Livermore, CA 94550, USA
⁶ School of Physics, University of New South Wales, Sydney 2052, Australia
⁷ Department of Physics, Macquarie University, Sydney, NSW, Australia
⁸ Anglo-Australian Observatory, Epping, NSW 1710, Australia
⁹ School of Physics and Astronomy, Cardiff University, Cardiff, CF24 3AA, UK

Received: 30 June 2005
Accepted: 27 August 2007

Abstract

Context.The Fornax cluster spectroscopic survey (FCSS) is an all-object survey of a region around the Fornax cluster of galaxies undertaken using the 2dF multi-object spectrograph on the Anglo-Australian telescope. Its aim was to obtain spectra for a complete sample of all objects with irrespective of their morphology (i.e. including “stars”, “galaxies” and “merged” images).

Aims.We explore the extent to which (nearby) cluster galaxies are present in 2MASS. We consider the reasons for the omission of 2MASS galaxies from the FCSS and vice versa.

Methods.We consider the intersection (2.9 square degrees on the sky) of our data set with the infra-red 2 micron all-sky survey (2MASS), using both the 2MASS extended source catalogue (XSC) and the point source catalogue (PSC). We match all the XSC objects to FCSS counterparts by position and also extract a sample of galaxies, selected by their FCSS redshifts, from the PSC.

Results.We confirm that all 114 XSC objects in the overlap sample are galaxies, on the basis of their FCSS velocities. A total of 23 Fornax cluster galaxies appear in the matched data, while, as expected, the remainder of the sample lie at redshifts out to (the spectra show that 61% are early type galaxies, 18% are intermediate types and 21% are strongly star forming).The PSC sample turns out to contain twice as many galaxies as does the XSC. However, only one of these 225 galaxies is a (dwarf) cluster member. On the other hand, galaxies which are unresolved in the 2MASS data (though almost all are resolved in the optical) amount to 71% of the non-cluster galaxies with 2MASS detections and have redshifts out to .