The SkyMapper DR1.1 Search for Extremely Metal-Poor Stars
  We present and discuss the results of a search for extremely metal-poor stars
based on photometry from data release DR1.1 of the SkyMapper imaging survey of
the southern sky. In particular, we outline our photometric selection
procedures and describe the low-resolution ($R$ $\approx$ 3000) spectroscopic
follow-up observations that are used to provide estimates of effective
temperature, surface gravity and metallicity ([Fe/H]) for the candidates. The
selection process is very efficient: of the 2618 candidates with low-resolution
spectra that have photometric metallicity estimates less than or equal to -2.0,
41% have [Fe/H] $\leq$ -2.75 and only $\sim$7% have [Fe/H] $>$ -2.0 dex. The
most metal-poor candidate in the sample has [Fe/H] $<$ -4.75 and is notably
carbon-rich. Except at the lowest metallicities ([Fe/H] $<$ -4), the stars
observed spectroscopically are dominated by a `carbon-normal' population with
[C/Fe]$_{1D,LTE}$ $\leq$ +1 dex. Consideration of the A(C)$_{1D, LTE}$ versus
[Fe/H]$_{1D, LTE}$ diagram suggests that the current selection process is
strongly biased against stars with A(C)$_{1D, LTE}$ $>$ 7.3 (predominantly
CEMP-$s$) while any bias against stars with A(C)$_{1D, LTE}$ $<$ 7.3 and
[C/Fe]$_{LTE}$ $>$ +1 (predominantly CEMP-no) is not readily quantifiable given
the uncertainty in the SkyMapper $v$-band DR1.1 photometry. We find that the
metallicity distribution function of the observed sample has a power-law slope
of $\Delta$(Log N)/$\Delta$[Fe/H] = 1.5 $\pm$ 0.1 dex per dex for -4.0 $\leq$
[Fe/H] $\leq$ -2.75, but appears to drop abruptly at [Fe/H] $\approx$ -4.2, in
line with previous studies.
