Thermal Properties of the Hot Core Population in Sagittarius B2 Deep South

Abstract

We report the discovery of nine new hot molecular cores in the Deep South (DS) region of Sagittarius B2 using Atacama Large Millimeter/submillimeter Array Band 6 observations. We measure the rotational temperature of CH _3 OH and derive the physical conditions present within these cores and the hot core Sgr B2(S). The cores show heterogeneous temperature structure, with peak temperatures between 252 and 662 K. We find that the cores span a range of masses (203–4842 M _⊙ ) and radii (3587–9436 au). CH _3 OH abundances consistently increase with temperature across the sample. Our measurements show the DS hot cores are structurally similar to Galactic disk hot cores, with radii and temperature gradients that are comparable to sources in the disk. They also show shallower density gradients than disk hot cores, which may arise from the Central Molecular Zone’s higher density threshold for star formation. The hot cores have properties which are consistent with those of Sgr B2(N), with three associated with Class II CH _3 OH masers and one associated with an ultra-compact H ii region. Our sample nearly doubles the high-mass star-forming gas mass near Sgr B2(S) and suggests the region may be a younger, comparably massive counterpart to Sgr B2(N) and (M). The relationship between peak CH _3 OH abundance and rotational temperature traced by our sample and a selection of comparable hot cores is qualitatively consistent with predictions from chemical modeling. However, we observe constant peak abundances at higher temperatures ( T ≳ 250 K), which may indicate mechanisms for methanol survival that are not yet accounted for in models.

Keywords

• Protoclusters
• Chemical abundances
• Astrochemistry
• Galactic center
• Star forming regions
• Star formation