Hot Molecular Core Candidates in the Galactic Center 50 km/s Molecular Cloud

TL;DR

This study uses high-resolution ALMA observations to identify hot molecular core candidates in the Galactic Center's 50 km/s Molecular Cloud, revealing their properties, distribution, and potential early star formation stages.

Contribution

First detailed ALMA-based identification and analysis of hot molecular core candidates in the Galactic Center's 50 km/s Molecular Cloud.

Findings

Nine dust cores identified, including four with known HII regions.

28 HMCCs detected with varied association with other star formation indicators.

Mass-radius relation follows a single power law, with masses larger than similar structures in the Galactic disk.

Abstract

We present the results based on the 2.5 arcsec-resolution observations using Atacama Large Millimeter/submillimeter Array (ALMA) of the Galactic Center Molecular Cloud G-0.02-0.07, or the 50 km/s Molecular Cloud (50MC), in the SO (N_J=2_2-1_1) line and 86-GHz continuum emission, the combination of which is considered to trace "hot molecular core candidates" (HMCCs) appearing in the early stage of massive star formation. In the 86-GHz continuum image, we identified nine dust cores in the central part of the 50MC, in which four famous compact HII regions are located. No new ultra-compact HII regions were found. We also identified 28 HMCCs in the 50MC with the SO line. The overall SO distribution had no clear positional correlation with the identified HII regions. The HMCCs in the 50MC showed a variety of association and non-association with dust and Class-I CH3OH maser emissions. The variety suggests that they are not in a single evolutionary stage or environment. Nevertheless, the masses of the identified HMCCs were found to be well approximated by a single power law of their radii, M_LTE/(M_sun)=5.44 x 10^5 (r/(pc))^2.17 at T_ex = 50-100 K. The derived HMCC masses were larger than those of the molecular cores with the same radii in the 50MC and also than those of the molecular clumps in the Galactic disk. Additional observations are needed to confirm the nature of these HMCCs in the 50MC.