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The Low surface brightness and dwarf galaxy regime

The study of the field dwarf galaxy population offers a unique testing ground for galaxy formation and the underlying physics. Cold dark matter (CDM) simulations predict that there are many more low-mass than high-mass halos remaining today. Observationally there appears to be a deficit with respect to this prediction; the observed galaxy stellar mass function is not as steep as the halo mass function. This could be in part because the mass of the dark matter particle is in the keV range (i.e., WDM), which suppresses power on dwarf galaxy scales. However, dwarf galaxy formation is also sensitive to the impact of the photoionizing background, supernovae feedback, and environmental effects. Disentangling the baryonic effects from any change in the power spectrum requires large statistically representative samples.

Local surveys such as the SDSS and follow-on campaigns such as GAMA are fundamentally limited by surface brightness sensitivity of the imaging data, and the reality of the luminosity-surface brightness relation. Various studies clearly demonstrate that the SDSS becomes incomplete for systems with µe ≥ 23.0 mags/sq arcsec which become frequent below absolute magnitudes of Mr = −18 mag. For this reason the low surface brightness and dwarf galaxy domains continue to remain uncharted territory for modern surveys. Only deep surveys of clusters (highly unrepresentative of the average Universe) have entered this dwarf galaxy low-SB regime. The first deep wide-area imaging survey capable of probing into this domain will be VST KiDS covering 750 sq. deg in the Southern and Northern Galactic Caps. WAVES will use the VST KiDS data as its input survey to provide targets to rAB < 22mag with µe < 26 mag/sq arcsec allowing for the construction of a complete sample of galaxies to Mr = −14mag, i.e., 4mags deeper than SDSS. The WAVES survey, rAB < 22, with high-completeness for low-SB galaxies would enable the galaxy stellar mass function to be measured accurately down to 106M.

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Fig. 1: Our current understanding of the space-density of galaxies are shown as data points (as indicated) while the mass range probed by WAVES and its photometric extensions are indicated by the blue shaded regions. The locations of known galaxies from the Local Group are indicated.