Connection between PAHs and small hydrocarbons in the Horsehead Nebula   Photo-Dissociation Region
  We present recent observations of small hydrocarbons (C3H2, C2H, C4H) with high abundances in the Photo-Dissociation Region of the Horsehead nebula. Our results show for the first time observational indications that the small hydrocarbon distribution follows the Aromatic Infrared Bands (AIBs) emission traced by ISO-LW2 (5-8.5 microns), whereas it does not coincide with the CO and isotopes large-scale distribution. The derived abundances are significantly higher than in local clouds. This enhancement might be explained by an in situ formation assisted by the release of carbonaceous molecules from UV-irradiated aromatic particles. 
David Teyssier (1,2), David Fosse (2), Maryvonne Gerin (2), Jerome   Pety (2,3), Alain Abergel (4) and Emilie Habart (5) ((1...