Characterizing the chemical pathways for water formation -- A deep
  search for hydrogen peroxide
  In 2011, hydrogen peroxide (HOOH) was observed for the first time outside the
solar system (Bergman et al., A&A, 2011, 531, L8). This detection appeared a
posteriori quite natural, as HOOH is an intermediate product in the formation
of water on the surface of dust grains. Following up on this detection, we
present a search for HOOH in a diverse sample of sources in different
environments, including low-mass protostars and regions with very high column
densities, such as Infrared Dark Clouds (IRDCs). We do not detect the molecule
in any other source than Oph A, and derive 3$\sigma$ upper limits for the
abundance of HOOH relative to H$_2$ lower than in Oph A for most sources. This
result sheds a different light on our understanding of the detection of HOOH in
Oph A, and shifts the puzzle to why this source seems to be special. Therefore
we rediscuss the detection of HOOH in Oph A, as well as the implications of the
low abundance of HOOH, and its similarity with the case of O$_2$. Our chemical
models show that the production of HOOH is extremely sensitive to the
temperature, and favored only in the range 20$-$30 K. The relatively high
abundance of HOOH observed in Oph A suggests that the bulk of the material lies
at a temperature in the range 20$-$30 K.
