The Fornax Spectroscopic Survey: The number of unresolved compact galaxies

Abstract

We describe a sample of 13 bright (18.5 < BJ < 20.1), compact galaxies at low redshift (0.05 < z < 0.21) behind the Fornax Cluster. These galaxies are unresolved on UK Schmidt sky survey plates, and so they would be missing from most galaxy catalogs compiled from this material. The objects were found during initial observations of The Fornax Spectroscopic Survey. This project is using the Two-degree Field spectrograph on the AngloAustralian Telescope to obtain spectra for a complete sample of all 14,000 objects, stellar and nonstellar, with 16.5 < BJ < 19.7, in a 12 deg2 area centered on the Fornax Cluster of galaxies. The surface density of compact galaxies with magnitudes 16.5 < BJ < 19.7 is 7 ± 3 deg-2, representing 2.8% ± 1.6% of all local (z < 0.2) galaxies to this limit. There are 12 ± 3 deg-2 with 16.5 < BJ < 20.2. They are luminous (-21.5 < MB < -18.0, for H0 = 50 km s-1 Mpc-1), and most have strong emission lines (Hα equivalent widths of 40-200 Å) and small sizes typical of luminous H II galaxies and compact narrow emission line galaxies. Four out of 13 have red colors and early-type spectra, and so they are unlikely to have been detected in any previous surveys.