Hot Cores in the submm - obscured by dust?

TL;DR

This study uses APEX observations of high-J HCN lines to investigate dust obscuration in hot cores, finding that vibrationally excited lines can reveal inner regions despite high optical depths, supporting future high-frequency ALMA studies.

Contribution

It demonstrates that vibrationally excited HCN lines can probe hot core interiors despite dust obscuration, enabling future high-frequency ALMA observations.

Findings

Detection of vibrationally excited satellite lines from hot core centers.

High optical depth causes asymmetric, self-absorbed line profiles.

Inner regions are accessible via high-frequency observations despite dust obscuration.

Abstract

We present APEX observations of HCN (9-8) and (4-3) lines toward a sample of hot cores. The spectral shapes of the main transitions are asymmetric and self-absorbed, as expected for high optical depth in a possibly infalling envelope. For spherical symmetry, the large column densities of these sources would mean that the central region is obscured by dust above a certain frequency. However, we detected the vibrationally excited satellite lines (v_2=1; J=9-8) at 797 GHz, which originate from the inner regions. This indicates that high-frequency ALMA observations of hot core centers will be feasible.