Australia Telescope National Facility

Compact Stellar Systems in the Fornax Cluster: Super-massive Star Clusters or Extremely Compact Dwarf Galaxies?
M. J. Drinkwater, J. B. Jones, M. D. Gregg, S. Phillipps, PASA, 17 (3), 227.

Next Section: Properties of the compact
Title/Abstract Page: Compact Stellar Systems in
Previous Section: Introduction
Contents Page: Volume 17, Number 3

Discovery Observations: The Fornax Spectroscopic Survey

Our Fornax Spectroscopic Survey, carried out with the 2dF multi-object spectrograph on the Anglo-Australian Telescope (see Drinkwater et al. 2000), is now 87% complete in its first field to a limit of B_J=19.7. The 2dF field is a circle of diameter 2 degrees (i.e. $\pi$ square degrees of sky). We have measured optical spectra of some 4000 objects (some going fainter than our nominal limit) in a 2dF field centred on the central galaxy of the Fornax Cluster (NGC 1399). This survey is unique in that the targets (selected from digitised UK Schmidt Telescope photographic sky survey plates) include all objects, both unresolved (``stars'') and resolved (``galaxies'') in this large area of sky. The resolved objects measured are mostly background galaxies as expected with a minor contribution from Fornax Cluster members. The unresolved objects are mostly Galactic stars and distant AGN, also as expected, but some are compact starburst (and post-starburst) galaxies beyond the Fornax Cluster (Drinkwater et al 1999a).

Finally, in addition to the dwarf galaxies already listed in the Fornax Cluster Catalog (FCC: Ferguson 1989) which we have confirmed as cluster members, we have found a sample of five very compact objects at the cluster redshift which are unresolved on photographic sky survey plates and not included in the FCC. These new members of the Fornax Cluster are listed in Table 1 along with their photometry measured from the UKST plates.

**Table 1:** The new compact objects
N.	Name	RA (J2000) Dec	B_J	M_B	cz	Notes
			(mag)	(mag)	( ${\rm\thinspace km}{\rm\thinspace s}^{-1}\,$ )
1	FCSS J033703.3-353804	03 37 03.30 -35 38 04.6	19.85	-11.1	1507
2	FCSS J033806.3-352858	03 38 06.33 -35 28 58.8	18.85	-12.1	1328
3	FCSS J033854.1-353333	03 38 54.10 -35 33 33.6	17.68	-13.2	1595	¹
4	FCSS J033935.9-352824	03 39 35.95 -35 28 24.5	18.82	-12.1	1936	²
5	FCSS J033952.5-350424	03 39 52.58 -35 04 24.1	19.66	-11.2	1337

Notes: (1) CGF 1-4 (2) CGF 5-4, both in Hilker et al. (1999)

Our 2dF measurements of unresolved objects are 80% complete in the magnitude range of these objects (

$17.5<\hbox{$b_j$}<20.0$ ). There is therefore about one more similar compact object still to be found in in our central 2dF field. The number density of these objects is therefore $6\pm3$ per 2dF field ( $\pi$ square degrees). Two of the objects (the two brightest) were also identified as cluster members by Hilker et al. (1999). Hilker et al. measured spectra of about 50 galaxies brighter than V=20 in a square region of width 0.25 degrees at the centre of the Fornax Cluster. In the ``galaxies'' they include objects which were very compact, but still resolved. By contrast our own survey covers a much larger area and also includes all unresolved objects.

Next Section: Properties of the compact
Title/Abstract Page: Compact Stellar Systems in
Previous Section: Introduction
Contents Page: Volume 17, Number 3

ASKAP

Public