of the three fields. The dimensions of the plots indicate the size of the observed fields. The quasars are located at the origin. The letters refer to the ELG designations used throughout the text.[]{data-label="fig:elgcandidates"}](fig3)

[SExtractor]{} was used with the parameters determined in Section \[sec:detpar\] and a detection threshold of 5$\sigma$ to build a catalogue of sources for each image. Within each field, the catalogues from each image were cross-matched: objects were associated by position, with a three pixel threshold.

These observations are not deep enough to observe continuum flux from a typical Lyman $\alpha$ emitting galaxy [@LeDelliou06]. Given the likely range of line widths [@Dawson04; @Tapken04], we do not expect to observe Lyman $\alpha$ emitters in more than two adjacent passbands. Objects which were identified in either one or two bands were therefore flagged for further investigation.

In order to minimise the risk of contamination by noisy artefacts, all flagged objects were examined eye, and those which appeared unphysical or corresponded to sites of corruption by (for example) heavy cosmic ray or charge trapping activity in the original images were rejected.

MRC B1256-243
-------------

Four candidate emission line galaxies were identified in the field of MRC B1256-243. Details are given 