2MASS Galaxies in the Fornax Cluster Spectroscopic Survey

TL;DR

This study investigates the overlap between 2MASS infrared galaxy data and the Fornax Cluster Spectroscopic Survey, revealing the extent of cluster galaxy detection and the characteristics of galaxies missed by 2MASS.

Contribution

It provides a detailed comparison of 2MASS and FCSS galaxy samples, highlighting the limitations of 2MASS in detecting certain cluster and non-cluster galaxies.

Findings

All 114 XSC objects in the overlap are confirmed galaxies.

23 Fornax Cluster galaxies are identified in the matched data.

Most unresolved 2MASS galaxies are non-cluster galaxies at higher redshifts.

Abstract

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 16.5 < b_j < 19.7 irrespective of their morphology (i.e. including `stars', `galaxies' and `merged' images). 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. 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. 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 z = 0.2 (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 z=0.32.