ALMA observations of the archetypal "hot core" that isn't: Orion KL

TL;DR

This study uses high-resolution ALMA observations across multiple frequencies to analyze the Orion-KL hot core, revealing new compact sources and supporting the idea of external heating rather than internal sources.

Contribution

First submillimeter detection of three compact sources near Orion-KL hot core, providing insights into dust properties and heating mechanisms.

Findings

Detected three new compact continuum sources near Orion-KL

Sources show moderate optical thickness and possible grain growth

Hot core likely heated externally, not by nearby objects

Abstract

We present sensitive high angular resolution ($\sim$ 0.1$''$ -- 0.3$''$) continuum ALMA (The Atacama Large Millimeter/Submillimeter Array) observations of the archetypal hot core located in Orion-KL. The observations were made in five different spectral bands (bands 3, 6, 7, 8, and 9) covering a very broad range of frequencies (149 -- 658 GHz). Apart of the well-know millimeter emitting objects located in this region (Orion Source I and BN), we report the first submillimeter detection of three compact continuum sources (ALMA 1-3) in the vicinities of the Orion-KL hot molecular core. These three continuum objects have spectral indices between 1.47 to 1.56, and brightness temperatures between 100 to 200 K at 658 GHz suggesting that we are seeing moderate optically thick dust emission with possible grain growth. However, as these objects are not associated with warm molecular gas, and some of them are farther out from the molecular core, we thus conclude that they cannot heat the molecular core. This result favours the hypothesis that the hot molecular core in Orion-KL core is heated externally.