Core Emergence in a Massive Infrared Dark Cloud: A Comparison between Mid-IR Extinction and 1.3 mm Emission
Journal article, 2018

Stars are born from dense cores in molecular clouds. Observationally, it is crucial to capture the formation of cores in order to understand the necessary conditions and rate of the star formation process. The Atacama Large Millimeter/submillimeter Array (ALMA) is extremely powerful for identifying dense gas structures, including cores, at millimeter wavelengths via their dust continuum emission. Here, we use ALMA to carry out a survey of dense gas and cores in the central region of the massive (∼10 5 M o ) infrared dark cloud (IRDC) G28.37+0.07. The observation consists of a mosaic of 86 pointings of the 12 m array and produces an unprecedented view of the densest structures of this IRDC. In this first Letter about this data set, we focus on a comparison between the 1.3 mm continuum emission and a mid-infrared (MIR) extinction map of the IRDC. This allows estimation of the "dense gas" detection probability function (DPF), i.e., as a function of the local mass surface density, Σ, for various choices of thresholds of millimeter continuum emission to define "dense gas." We then estimate the dense gas mass fraction, f dg , in the central region of the IRDC and, via extrapolation with the DPF and the known Σ probability distribution function, to the larger-scale surrounding regions, finding values of about 5% to 15% for the fiducial choice of threshold. We argue that this observed dense gas is a good tracer of the protostellar core population and, in this context, estimate a star formation efficiency per free-fall time in the central IRDC region of ff ∼ 10%, with approximately a factor of two systematic uncertainties.

dust

stars: formation

extinction

stars: protostars

ISM: structure

radio continuum: ISM

ISM: clouds

Author

Shuo Kong

Yale University

Jonathan Tan

Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics, Galactic Astrophysics

University of Virginia

Héctor G. Arce

Yale University

P. Caselli

Max Planck Society

Francesco Fontani

Arcetri Astrophysical Observatory

Michael J. Butler

Max Planck Society

Astrophysical Journal Letters

2041-8205 (ISSN) 2041-8213 (eISSN)

Vol. 855 2 L25

Subject Categories

Astronomy, Astrophysics and Cosmology

Atom and Molecular Physics and Optics

Probability Theory and Statistics

DOI

10.3847/2041-8213/aab151

More information

Latest update

5/7/2019 9