ALMA Observations of Massive Clouds in the Central Molecular Zone: External-Pressure-Confined Dense Cores and Salpeter-like Core Mass Functions

TL;DR

This study uses ALMA observations to analyze dense cores in the Central Molecular Zone, revealing external pressure's role in core stability and a Salpeter-like core mass function, shedding light on star formation processes in extreme environments.

Contribution

First detailed ALMA study of dense cores in the CMZ showing external pressure's importance and a Salpeter-like core mass function with implications for star formation.

Findings

External pressure is crucial for core virial equilibrium in the CMZ.

Core mass functions follow a Salpeter-like slope at high masses.

Results suggest gas accretion and fragmentation influence the core-to-star mass transformation.

Abstract

We present Atacama Large Millimeter/submillimeter Array (ALMA) Band 6 (1.3 mm) observations of dense cores in three massive molecular clouds within the Central Molecular Zone (CMZ) of the Milky Way, including the Dust Ridge cloud e, Sgr C, and the 20 km s-1 cloud, at a spatial resolution of 2000 au. Among the 834 cores identified from the 1.3 mm continuum, we constrain temperatures and linewidths of 253 cores using local thermodynamic equilibrium (LTE) methods to fit the H2CO and/or CH3CN spectra. We determine their masses using the 1.3 mm dust continuum and derived temperatures, and then evaluate their virial parameters using the H2CO and/or CH3CN linewidths and construct the core mass functions (CMFs). We find that the contribution of external pressure is crucial for the virial equilibrium of the dense cores in the three clouds, which contrasts with the environment in the Galactic disk where dense cores are already bound even without the contribution of external pressure. We also find that the CMFs show a Salpeter-like slope in the high-mass (>~3-6 Msun) end, a change from previous works with our new temperature estimates. Combined with the possible top-heavy initial mass functions (IMFs) in the CMZ, our result suggests that gas accretion and further fragmentation may play important roles in transforming the CMF to the IMF.