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Low energy cosmic rays are the major ionization agents of molecular clouds.However, it has been shown that, if the cosmic ray spectrum measured by Voyager1 is representative of the whole Galaxy, the predicted ionization rate indiffuse clouds fails to reproduce data by 1-2 orders of magnitude, implyingthat an additional source of ionization must exist. One of the solutionsproposed to explain this discrepancy is based on the existence of an unknownlow energy (in the range 1 keV-1 MeV, not probed by Voyager) cosmic raycomponent, called carrot when first hypothesized by Reeves and collaborators inthe seventies. Here we investigate the energetic required by such scenario. Weshow that the power needed to maintain such low energy component is comparableof even larger than that needed to explain the entire observed cosmic rayspectrum. Moreover, if the interstellar turbulent magnetic field has to sustaina carrot, through second-order Fermi acceleration, the required turbulencelevel would be definitely too large compared to the one expected at the scaleresonant with such low energy particles. Our study basically rules out all theplausible sources of a cosmic ray carrot, thus making such hidden componentunlikely to be an appealing and viable source of ionization in molecularclouds.

Can a cosmic ray carrot explain the ionization level in diffuse molecular clouds?