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We implement a new observational method for mapping the aliphatic hydrocarbon content in the solid phase in our Galaxy, based on spectrophotometric imaging of the 3.4  |$\mu$| m absorption feature from interstellar dust. We previously demonstrated this method in a field including the Galactic Centre cluster. We applied the method to a new field in the Galactic Centre where the 3.4  |$\mu$| m absorption feature has not been previously measured and we extended the measurements to a field in the Galactic plane to sample the diffuse local interstellar medium, where the 3.4  |$\mu$| m absorption feature has been previously measured. We have analysed 3.4  |$\mu$| m optical depth and aliphatic hydrocarbon column density maps for these fields. Optical depths are found to be reasonably uniform in each field, without large source-to-source variations. There is, however, a weak trend towards increasing optical depth in a direction towards b  = 0° in the Galactic Centre. The mean value of column densities and abundances for aliphatic hydrocarbon were found to be about several |$\rm \times 10^{18} \, cm^{-2}$| and several tens × 10−6, respectively for the new sightlines in the Galactic plane. We conclude that at least 10–20 per cent of the carbon in the Galactic plane lies in aliphatic form. [ABSTRACT FROM AUTHOR]

HESS J1804−216 is one of the brightest yet most mysterious TeV γ-ray sources discovered to date. Previous arc-minute scale studies of the interstellar medium (ISM) surrounding this TeV γ-ray source revealed  HESS J1804−216 is likely powered by a mature supernova remnant (SNR) or pulsar, hence its origin remains uncertain. In this paper, we focus on the diffusive escape of cosmic ray protons from potential SNR accelerators. These cosmic rays interact with the ISM to produce TeV γ-rays. We utilize the isotropic diffusion equation solution for particles escaping from a shell, to model the energy-dependent escape and propagation of protons into the ISM. This work is the first attempt at modelling the spatial morphology of γ-rays towards  HESS J1804−216, using arc-minute ISM observations from both Mopra and the Southern Galactic Plane Survey. The spectral and spatial distributions of γ-rays for the two nearby potential SNR counterparts, SNR G8.7−0.1 and the progenitor SNR of PSR J1803−2137, are presented here. We vary the diffusion parameters and particle spectrum and use a grid search approach to find the best combination of model parameters. We conclude that moderately slow diffusion is required for both candidates. The most promising candidate to be powering the TeV  γ-rays from HESS J1804−216 in a hadronic scenario is the progenitor SNR of PSR J1803−2137. [ABSTRACT FROM AUTHOR]