Chemical features in the circumnuclear disk of the Galactic center
Artikel i vetenskaplig tidskrift, 2015

Aims. The circumnuclear disk (CND) of the Galactic center is exposed to many energetic phenomena coming from the supermassive black hole Sgr A* and from stellar activities. These energetic activities can affect the chemical composition in the CND through interaction with UV photons, cosmic rays, X-rays, and shock waves. We aim to constrain the physical conditions present in the CND through chemical modeling of observed molecular species detected toward it. Methods. We analyzed a selected set of molecular line data taken toward a position in the southwest lobe of the CND with the IRAM 30m and APEX 12-m telescopes and derived the column density of each molecule via a large velocity gradient (LVG) analysis. The determined chemical composition is compared with a time-dependent, gas-grain chemical model based on the UCL_CHEM code, which includes the effects of shock waves with varying physical parameters. Results. We detect molecules, such as CO, HCN, HCO+, HNC, CS, SO, SiO, NO, CN, H2CO, HC3N, N2H+, and H3O+, and obtain their column densities. Total hydrogen densities obtained from LVG analysis range between 2x10(4) and 1x10(6) cm(-3) and most species indicate values around several x10(5) cm(-3). These values are lower than those corresponding to the Roche limit, which shows that the CND is tidally unstable. The chemical models show good agreement with the observations in cases where the density is similar to 10(4) cm(-3), the cosmic-ray ionization rate is high, > 10(-15) s(-1), or shocks with velocities > 40 km s(-)1 have occurred. Conclusions. Comparison of models and observations favors a scenario where the cosmic-ray ionization rate in the CND is high, but precise effects of other factors, such as shocks, density structures, UV photons, and X-rays from the Sgr A*, must be examined with higher spatial resolution data.

ISM: molecules

Galaxy: center

Författare

N. Harada

Academia Sinica

Max Planck-institutet

D. Riquelme

Max Planck-institutet

S. Viti

University College London (UCL)

I. Jimenez-Serra

European Southern Observatory (ESO)

University College London (UCL)

M. A. Requena-Torres

Max Planck-institutet

K. M. Menten

Max Planck-institutet

S. Martin

Institut de RadioAstronomie Millimetrique (IRAM)

European Southern Observatory Santiago

Rebeca Aladro

Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik

J. Martin-Pintado

CSIC-INTA - Centro de Astrobiologia (CAB)

S. Hochgurtel

Max Planck-institutet

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 584 A102

Ämneskategorier

Astronomi, astrofysik och kosmologi

Infrastruktur

Onsala rymdobservatorium

DOI

10.1051/0004-6361/201526994