Organic molecules in the Galactic center : Hot core chemistry without hot cores

• Published in: Astronomy and astrophysics (Berlin) 2006-09, Vol.455 (3), p.971-985
• Main Authors: REQUENA-TORRES, M. A, MARTIN-PINTADO, J, RODRIGUEZ-FRANCO, A, MARTIN, S, RODRMGUEZ-FERNANDEZ, N. J, DE VICENTE, P
• Format: Article
• Language: English
• Subjects: Astronomy; Astrophysics; Cosmology and Extra-Galactic Astrophysics; Earth, ocean, space; Exact sciences and technology; Physics; Sciences of the Universe
• ISSN: 0004-6361; 1432-0746; 1432-0756
• DOI: 10.1051/0004-6361:20065190

Aims. We study the origin of large abundances of complex organic molecules in the Galactic center (GC). Methods. We carried out a systematic study of the complex organic molecules CH sub(3) OH, C sub(2) H sub(5) OH, (CH sub(3)) sub(2) O, HCOOCH sub(3), HCOOH, CH sub(3) COOH, H sub(2) CO, and CS toward 40 GC molecular clouds. Using the LTE approximation, we derived the physical properties of GC molecular clouds and the abundances of the complex molecules. The abundances of complex organic molecules in the GC are compared with those measured in hot cores and hot corinos, in which these complex molecules are also abundant. Results. The CH sub(3) OH abundance between clouds varies by nearly two orders of magnitude from beta Pictoris. In particular, the scattered light surface brightness profile falls off as beta Pictoris and 35 AU for AU Mic. In both cases, the disk color rises as the distance increases beyond these reference radii. Aims. In this paper, we present the first comprehensive analysis of the AU Mic disk properties since the system was resolved by Kalas et al. (2004, Science, 303, 1990). We explore whether the dynamical model, which successfully reproduces the beta Pictoris brightness profile (e.g., Augereau et al. 2001, A&A, 370, 447), could apply to AU Mic. Methods. We calculate the surface density profile of the AU Mic disk by performing the inversion of the near-IR and visible scattered light brightness profiles measured by Liu (2004, Science, 305, 1442) and Krist et al. (2005, AJ, 129, 1008), respectively. We discuss the grain properties by analysing the blue color of the disk in the visible (Krist et al. 2005) and by fitting the disk spectral energy distribution. Finally, we evaluate the radiation and wind forces on the grains. The impact of the recurrent X-ray and UV-flares on the dust dynamics is also discussed. Results. We show that irrespective of the mean scattering asymmetry factor of the grains, most of the emission arises from an asymmetric, collisionally-dominated region that peaks close to the surface brightness break around 35 AU. The elementary scatterers at visible wavelengths are found to be sub-micronic, but the inferred size distribution underestimates the number of large grains, resulting in sub-millimeter emissions that are too low compared to the observations. From our inversion procedure, we find that the V-to H-band scattering cross sections ratio increases outside 40 AU, in line with the observed color gradient of the dis