The Stromlo Milky Way Satellites Survey

The SMS program is a critical endeavor to investigate whether the predictions of standard cold dark matter cosmology are consistent with the observed matter distribution in the Milky Way halo. It is the deepest, most extended search for optically elusive dwarf satellite galaxies and tidal streams to date, covering the entire Southern hemisphere. The 150 TB of CCD images in six photometric bands, 0.5-1.0 mag fainter than SDSS will be produced by the ANU SkyMapper telescope over the next five years. The primary objective of our program is to study the baryonic and dark matter components of the newly detected stellar overdensities providing an unprecedented physical picture of the phenomenon "dwarf satellite" and stringent observational constraints for CDM theory.

The current galaxy formation paradigm implies that galaxies such as the Milky Way, are baryon condensations at the center of extensive dark matter halos, and exhibit a wealth of substructure that reflects their hierarchical formation: hundreds of sub-halos and streams of tidally disrupted dwarf systems. However only a few dwarf satellites have been found around the Milky Way to date - 22 dwarfs compared to 500-10,000 predicted by theory (Klypin et al. 1999, Moore et al.1999, Diemand et al. 2007). Almost all detected dwarfs are arranged in a plane (Kroupa et al. 2005), inconsistent with the spatial distribution predicted by Cold Dark Matter theory.

Incompleteness in the census of dwarf satellites around the Milky Way seriously hinders the physical interpretation, calibration, and possibly the modification of current cosmological models. Progress can only be made if observers can determine the exact number of dwarf galaxies that do exist around the Milky Way, including accurate estimates of the detection limits such as star density, compactness and satellite size, distance from the Milky Way etc. But this requires a deep and systematic photometric survey of the entire celestial sphere to search for the missing satellites, a technical challenge that became feasible only just recently.

To improve the completeness of the known Milky Way dwarf galaxy population, Willman et al. (2002) conduced a search for Milky Way satellites in the Northern Hemisphere (8800 square degrees) based on the Sloan Digital Sky Survey (SDSS). Careful analyses of resolved stars in both the SDSS and the Two Micron All Sky Survey have resulted in the discovery of a new Milky Way companion (Willman et al. 2005) as well as large-scale stellar structures and dwarf galaxy remnants around the Milky Way (Newberg et al. 2002; Yanny et al. 2003; Ibata et al. 2003; Rocha-Pinto et al. 2003, 2004; Majewski et al. 2003; Martin et al. 2004). However, it had been more than 10 years(!) since the discovery of the 9th Milky Way dwarf spheroidal galaxy (Ibata et al. 1994; but see evidence in Martin et al. 2004 and Martinez-Delgado et al. 2005 for a probable new Milky Way dwarf at low latitude), while Willman et al. (2005) reported the discovery of the Ursa Major dwarf spheroidal (UMa), the 10th dwarf spheroidal companion to the Milky Way last year.

Inspired by the success of the Sloan Digital Sky Survey project to find optically elusive Milky Way satellites in the Northern hemisphere, A/Prof Helmut Jerjen from the Research School of Astronomy & Astrophysics assembled a specialist team of 14 international scientists (observers and theoreticians) from nine research institutions that will carry out the deepest, most extended search for Milky Way satellites ever done over the next five years (2009-2013) covering the entire 20,000 degree of the Southern hemisphere. They will analyse 150 Terabytes of digital images from our state-of-the-art ANU SkyMapper telescope with sophisticated data mining tools. Extensive observations of newly detected satellites with the most powerful optical, infrared, and radio telescopes in the world will follow to obtain an unprecedented physical picture of the phenomenon "dwarf galaxy" and to find stringent observational constraints for cosmology to uncover flaws in CDM theory.

Over the next five years, the SMS team is looking for enthusiastic Honours and PhD students with strong background in Maths and Physics who would enjoy working with a group of world-class experts on one of the most fundamental questions in near-field cosmology.