New low surface brightness dwarf galaxies in the Centaurus group

¹ Departement Physik, Universität Basel, Klingelbergstr. 82, 4056 Basel, Switzerland
e-mail: oliver89.mueller@unibas.ch; bruno.binggeli@unibas.ch
² Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611, Australia

Received: 13 May 2016
Accepted: 24 August 2016

Abstract

Context. The distribution of satellite galaxies around the Milky Way and Andromeda and their correlation in phase space pose a major challenge to the standard ΛCDM model of structure formation. Other nearby groups of galaxies are now being scrutinized to test for the ubiquity of the phenomenon.

Aims. We conducted an extensive CCD imaging survey for faint, unresolved dwarf galaxies of very low surface brightness in the whole Centaurus group region, encompassing the Cen A and M 83 subgroups lying at a distance of roughly 4 and 5 Mpc, respectively. The aim is to significantly increase the sample of known Centaurus group members down to a fainter level of completeness, serving as a basis for future studies of the 3D structure of the group.

Methods. Following our previous survey of 60 square degrees covering the M 83 subgroup, we extended and completed our survey of the Centaurus group region by imaging another 500 square degrees area in the g and r bands with the wide-field Dark Energy Survey camera at the 4 m Blanco telescope at CTIO. The surface brightness limit reached for unresolved dwarf galaxies is μ_r ≈ 29 mag arcsec^-2. The faintest suspected Centaurus members found have m_r ≈ 19.5 mag or M_r ≈ −8.8 mag at the mean distance of the group. The images were enhanced using different filtering techniques.

Results. We found 41 new dwarf galaxy candidates, which together with the previously discovered 16 dwarf candidates in the M 83 subgroup amounts to almost a doubling of the number of known galaxies in the Centaurus complex, if the candidates are confirmed. We carried out surface photometry in g and r, and report the photometric parameters derived therefrom, for all new candidates as well as previously known members in the surveyed area. The photometric properties of the candidates, when compared to those of Local Group dwarfs and previously known Centaurus dwarfs, suggest membership in the Centaurus group. The sky distribution of the new objects is generally following a common envelope around the Cen A and M 83 subgroups. How the new dwarfs are connected to the intriguing double-planar feature recently reported must await distance information for the candidates.