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abstract: 'We have used the Taurus Tunable Filter to search for Lyman $\alpha$ emitters in the fields of three high redshift quasar fields: two at $z\sim2.2$ (MRC B1256-243 and MRC B2158-206) and one at $z\sim4.5$ (BR B0019-1522). Our observations had a field of view of around 35 square arcminutes, and reached AB magnitudes of magnitudes of $\sim$21 (MRC B1256-243), $\sim$22 (MRC B2158-206), and $\sim$22.6 (BR B0019-1522), dependent on wavelength. We have identified candidate emission line galaxies in all three of the fields, with the higher redshift field being by far the richest. By combining our observations with simulations of the instrumental response, we estimate the total density of emission line galaxies in each field. Seventeen candidate emission line galaxies were found in within 1.5 Mpc of BR0019-1522, a number density of $4.9 \pm 1.2 \times 10^{-3}$ Mpc$^{-3}$, suggesting a significant galaxy overdensity at $z\sim4.5$.'
author:
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    John Swinbank$^1$[^1], Joanne Baker$^{2}$, Jordi Barr$^3$, Isobel Hook$^3$, and Joss Bland-Hawthorn$^4$\
    $^1$Astronomical Institute “Anton Pannekoek”, University of Amsterdam, Postbus 94249, 1090 GE Amsterdam, The Netherlands\
    $^2$Nature, 4 Crinan Street, London N1 9XW, UK\
    $^3$Astrophysics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK\
    $^4$Sydney Institute for Astronomy, School of 