| Description |
Seventy years after its discovery in the diffuse interstellar medium,
the origin of the CH+ cation is still elusive. Herschel/HIFI offers a
unique opportunity to disclose the underlying gas dynamics at the
origin of CH+ in the diffuse medium by allowing high sensitivity and
high spectral resolution observations of the CH+ (J=1-0) transition,
unreachable from the ground: it will be the leading and only
instrument and the observations will bring a completely new look at
this resilient puzzle.
The abundant CH+ ion is not only a sensitive tracer of the most
tenuous phases of the interstellar medium but it is likely a specific
tracer of turbulent dissipation, because its formation route is highly
endoenergic. We propose absorption spectroscopy observations of mainly
the CH+ J=1-0 line, against 10 background dust continuum sources,
bright enough to allow us to sample a broad variety of galactic
environments. The lines-of-sight will probe the outskirts of
star-forming regions, including one InfraRed Dark Cloud, where
turbulent dissipation is most intense, and diffuse gas at high
galactic latitude where turbulence is milder. The primarily goal of
this project is the comparison of the CH+ abundances with model
predictions of turbulent dissipation regions, in which dissipation
proceeds either in low-velocity shocks or intense velocity-shears.
Another goal is testing the possibility that CH+ forms at the
turbulent interface between the two thermally stable phases of the
interstellar medium.
As HF, CH+ is a potential sensitive tracer of diffuse matter in the
early universe. Understanding its origin and the dissipative processes
that it traces will shed a new light on galaxy formation and
evolution. |
