A WISE-based search for debris discs amongst M-dwarfs in nearby, young,
  moving groups
  We present a search for debris discs amongst M-dwarf members of nearby, young
(5-150 Myr) moving groups (MGs) using infrared (IR) photometry, primarily from
the Wide Infrared Survey Explorer (WISE). A catalogue of 100 MG M-dwarfs that
have suitable WISE data is compiled and 19 of these are found to have
significant IR excess emission at 22$\mu$m. Our search is likely to be complete
for discs where the ratio of flux from the disc to flux from the star $f_{\rm
d}/f_{*} > 10^{-3}$. The spectral energy distributions are supplemented with
2MASS photometry and data at longer wavelengths and fitted with simple disc
models to characterise the IR excesses. There is a bimodal distribution --
twelve targets have $W1-W4 > 3$, corresponding to $f_{\rm d}/f_{*} > 0.02$ and
are likely to be gas-rich, primordial discs. The remaining seven targets have
$W1-W4 < 1$ ($f_{\rm d}/f_{*} \lesssim 10^{-3}$) and include three objects with
previously known or suspected debris discs and four new debris disc candidates
that are all members of the Beta Pic MG. All of the IR excesses are identified
in stars that are likely members of MGs with age $< 30$ Myr. The detected
debris disc frequency falls from 13 to 5 per cent to $< 7$ per cent (at 95 per
cent confidence) for objects younger or older than 30 Myr respectively. This
provides evidence for the evolution of debris discs on this timescale and does
not support models where the maximum of debris disc emission occurs much later
in lower-mass stars.
