Diffuse interstellar bands in M33
  We present the first sample of diffuse interstellar bands (DIBs) in the
nearby galaxy M33. Studying DIBs in other galaxies allows the behaviour of the
carriers to be examined under interstellar conditions which can be quite
different from those of the Milky Way, and to determine which DIB properties
can be used as reliable probes of extragalactic interstellar media.
Multi-object spectroscopy of 43 stars in M33 has been performed using
Keck/DEIMOS. The stellar spectral types were determined and combined with
literature photometry to determine the M33 reddenings E(B-V)_M33. Equivalent
widths or upper limits have been measured for the {\lambda}5780 DIB towards
each star. DIBs were detected towards 20 stars, demonstrating that their
carriers are abundant in M33. The relationship with reddening is found to be at
the upper end of the range observed in the Milky Way. The line of sight towards
one star has an unusually strong ratio of DIB equivalent width to E(B-V)_M33,
and a total of seven DIBs were detected towards this star.
