The tight correlation of CCH, and c-C3H2 in diffuse and translucent clouds

Maryvonne Gerin (1, 2) , M. Kazmierczak (3) , M. Jastrzebska (4) , Edith Falgarone (1, 2) , Pierre Hily-Blant (5) , Benjamin Godard (1, 2) , Massimo de Luca (1, 2)

1 LERMA - Laboratoire d'Etude du Rayonnement et de la Matière en Astrophysique
2 Dynamique des milieux interstellaires et plasmas stellaires
3 Centrum Astronomii UMK
4 Astronomical Observatory, Jagiellonia University
5 LAOG - Laboratoire d'Astrophysique de Grenoble

Using the IRAM 30 m telescope we observed molecular absorption lines from CCH and c-C₃H₂ produced by diffuse and translucent clouds along the lines of sight towards massive star forming regions. The same sources are surveyed with Herschel/HIFI as part of the PRISMAS guaranteed time program, for molecular absorption lines due to hydrides and carbon clusters. The background sources are massive star-forming regions (G34.3 + 0.1, G10.62-0.39, W51, W49N) and SgrA^*. The line profiles of the CCH, and c-C₃H₂, are strikingly similar for all lines of sight, showing that the ratio of the opacities of the probed transitions, (J_{K_a, K_c} = 2_1,2-1_0,1) for c-C₃H₂, and (J = 1-0, F = 5/2-3/2) for CCH, is nearly constant along all lines of sight, at tau_CCH ~ 1.8 × tau_c-C_3H_2. As a consequence, the ratio of the column densities of CCH and c-C₃H₂ is nearly constant and similar to the value derived earlier for diffuse clouds detected along lines of sight towards extragalactic continuum sources, N(CCH) = (28 ± 1.4) N(c-C₃H₂) (Lucas & Liszt 2000, A&A, 358, 1069). PDR models are able to reproduce the observed CCH, column densities for the range of physical conditions appropriate for the absorbing matter (n = 100-3000 cm^-3; A_V = 1-5 mag) but can neither fit the observed c-C₃H₂,column densities nor the tight correlation between CCH, and c-C₃H₂.

Domaines: Astrophysique [astro-ph]; Planète et Univers [physics]

Maryvonne Gerin, M. Kazmierczak, M. Jastrzebska, Edith Falgarone, Pierre Hily-Blant, et al.. The tight correlation of CCH, and c-C3H2 in diffuse and translucent clouds. Astronomy and Astrophysics - A&A, 2011, 525, pp.116. ⟨10.1051/0004-6361/201015050⟩. ⟨hal-03732375⟩