The MUSE-Wide Survey: A first catalogue of 831 emission line galaxies
  We present a first instalment of the MUSE-Wide survey, covering an area of
22.2 arcmin$^2$ (corresponding to $\sim$20% of the final survey) in the
CANDELS/Deep area of the Chandra Deep Field South. We use the MUSE integral
field spectrograph at the ESO VLT to conduct a full-area spectroscopic mapping
at a depth of 1h exposure time per 1 arcmin$^2$ pointing. We searched for
compact emission line objects using our newly developed LSDCat software based
on a 3-D matched filtering approach, followed by interactive classification and
redshift measurement of the sources. Our catalogue contains 831 distinct
emission line galaxies with redshifts ranging from 0.04 to 6. Roughly one third
(237) of the emission line sources are Lyman $\alpha$ emitting galaxies with $3
< z < 6$, only four of which had previously measured spectroscopic redshifts.
At lower redshifts 351 galaxies are detected primarily by their [OII] emission
line ($0.3 \lesssim z \lesssim 1.5$), 189 by their [OIII] line ($0.21 \lesssim
z \lesssim 0.85$), and 46 by their H$\alpha$ line ($0.04 \lesssim z \lesssim
0.42$). Comparing our spectroscopic redshifts to photometric redshift estimates
from the literature, we find excellent agreement for $z<1.5$ with a median
$\Delta z$ of only $\sim 4 \times 10^{-4}$ and an outlier rate of 6%, however a
significant systematic offset of $\Delta z = 0.26$ and an outlier rate of 23%
for Ly$\alpha$ emitters at $z>3$. Together with the catalogue we also release
1D PSF-weighted extracted spectra and small 3D datacubes centred on each of the
831 sources.
