Footpoints of the giant molecular loops in the Galactic center region^★

¹ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
e-mail: riquelme@mpifr-bonn.mpg.de
² Centro de Astrobiología (CSIC/INTA), Ctra. de Torrejón a Ajalvir km 4, 28850 Torrejón de Ardoz, Madrid, Spain
³ European Southern Observatory, Alonso de Córdova 3107, Vitacura, Santiago, Chile
⁴ Joint ALMA Observatory, Alonso de Córdova 3107, Vitacura, Santiago, Chile
⁵ School of Physics, University of New South Wales, Sydney, NSW 2052, Australia
⁶ Armagh Observatory and Planetarium, College Hill, Armagh BT61 9DG, Ireland
⁷ Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile

Received: 7 June 2016
Accepted: 24 October 2017

Abstract

Aims. We aim to reveal the morphology, chemical composition, kinematics, and to establish the main processes prevalent in the gas at the footpoints of the giant molecular loops (GMLs) in the Galactic center region.

Methods. Using the 22-m Mopra telescope, we mapped the M−3.8+0.9 molecular cloud, placed at the footpoints of a GML, in 3-mm range molecular lines. To derive the molecular hydrogen column density, we also observed the ¹³CO(2 − 1) line at 1 mm using the 12-m APEX telescope. From the 3 mm observations 12 molecular species were detected, namely HCO⁺, HCN, H¹³CN, HNC, SiO, CS, CH₃OH, N₂H⁺, SO, HNCO, OCS, and HC₃N.

Results. Maps revealing the morphology and kinematics of the M−3.8+0.9 molecular cloud in different molecules are presented. We identify six main molecular complexes. We derive fractional abundances in 11 selected positions of the different molecules assuming local thermodynamical equilibrium.

Conclusions. Most of the fractional abundances derived for the M−3.8+0.9 molecular cloud are very similar over the whole cloud. However, the fractional abundances of some molecules show significant difference with respect to those measured in the central molecular zone (CMZ). The abundances of the shock tracer SiO are very similar between the GMLs and the CMZ. The methanol emission is the most abundant species in the GMLs. This indicates that the gas is likely affected by moderate ~30 km s⁻¹ or even high velocity (50 km s⁻¹) shocks, consistent with the line profile observed toward one of the studied position. The origin of the shocks is likely related to the flow of the gas throughout the GMLs towards the footpoints.