Limits on chemical complexity in diffuse clouds: search for CH3OH and HC5N absorption

H. S. Liszt (1) , J. Pety (2, 3, 4) , R. Lucas (2)

1 NRAO - National Radio Astronomy Observatory
2 IRAM - Institut de RadioAstronomie Millimétrique
3 OP - Observatoire de Paris - Site de Paris
4 LERMA - Laboratoire d'Etude du Rayonnement et de la Matière en Astrophysique

Context: An unexpectedly complex polyatomic chemistry exists in diffuse clouds, allowing detection of species such as C2H, C3H2, H2CO, and NH3, which have relative abundances that are strikingly similar to those inferred toward the dark cloud TMC-1. Aims: We probe the limits of complexity of diffuse cloud polyatomic chemistry. Methods: We used the IRAM Plateau de Bure Interferometer to search for galactic absorption from low-lying J = 2-1 rotational transitions of A- and E-CH3OH near 96.740 GHz and used the VLA to search for the J = 8-7 transition of HC5N at 21.3 GHz. Results: Neither CH3OH nor HC5N were detected at column densities well below those of all polyatomics known in diffuse clouds and somewhat below the levels expected from comparison with TMC-1. The HCN/HC5N ratio is at least 3-10 times higher in diffuse gas than toward TMC-1. Based on observations obtained with the IRAM Plateau de Bure Interferometer and the NRAO VLA telescope.

Mots clés: astrochemistry; ISM: molecules; ISM: clouds

Domaines: Cosmologie et astrophysique extra-galactique [astro-ph.CO]; Cosmologie et astrophysique extra-galactique [astro-ph.CO]

H. S. Liszt, J. Pety, R. Lucas. Limits on chemical complexity in diffuse clouds: search for CH3OH and HC5N absorption. Astronomy and Astrophysics - A&A, 2008, 486, pp.493-496. ⟨10.1051/0004-6361:200809851⟩. ⟨hal-00315750⟩