The physical and chemical structure of Sagittarius B2

VIII. Full molecular line survey of hot cores

¹ I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
² Institut de Ciències de l’Espai (ICE, CSIC), Campus UAB, Carrer de Can Magrans s/n, 08193 Bellaterra, Barcelona, Spain
³ Institut d’Estudis Espacials de Catalunya (IEEC), 08860 Castelldefels, Barcelona, Spain
⁴ Green Bank Observatory, 155 Observatory Rd, Green Bank, WV 24944, USA

^★ Corresponding author; moeller@ph1.uni-koeln.de

Received: 26 June 2024
Accepted: 20 November 2024

Abstract

Context. The giant molecular cloud complex Sagittarius B2 (Sgr B2) in the central molecular zone of our Galaxy hosts several high-mass star formation sites, with Sgr B2(M) and Sgr B2(N) being the main centers of activity. This analysis aims to comprehensively model each core spectrum, considering molecular lines, dust attenuation, and free-free emission interactions. We describe the molecular content analysis of each hot core and identify the chemical composition of detected sources.

Aims. Using ALMA’s high sensitivity, we aim to characterize the hot core population in Sgr B2(M) and N, gaining a better understanding of the different evolutionary phases of star formation processes in this complex.

Methods. We conducted an unbiased ALMA spectral line survey of 47 sources in band 6 (211-275 GHz). Chemical composition and column densities were derived using XCLASS, assuming local thermodynamic equilibrium. Quantitative descriptions for each molecule were determined, considering all emission and absorption features across the spectral range. Temperature and velocity distributions were analyzed, and derived abundances were compared with other spectral line surveys.

Results. We identified 65 isotopologs from 41 different molecules, ranging from light molecules to complex organic compounds, originating from various environments. Most sources in the Sgr B2 complex were assigned different evolutionary phases of high-mass star formation.

Conclusions. Sgr B2(N) hot cores show more complex molecules such as CH₃OH, CH₃OCHO, and CH₃OCH₃, while M cores contain lighter molecules such as SO₂, SO, and NO. Some sulfur-bearing molecules are more abundant in N than in M. The derived molecular abundances can be used for comparison and to constrain astrochemical models. Inner sources in both regions were generally more developed than outer sources, with some exceptions.