The Structure of NGC 1976 in the Radio Range

TL;DR

This study uses high-resolution radio images at multiple frequencies to analyze the temperature structure of NGC 1976, revealing significant spatial variations and supporting a multi-layer model with minimal temperature fluctuations.

Contribution

It provides a detailed radio-based analysis of NGC 1976's temperature distribution, contrasting radio and optical fluctuation measurements, and supports a multi-layer model.

Findings

Temperature varies from 6000K to 8500K across the nebula.

Radio data favor a multi-layer model over a single temperature assumption.

Temperature fluctuations are much lower in radio data than optical data.

Abstract

High angular resolution radio continuum images of NGC 1976 (M42, Orion A) at frequency=330 MHz (wavelength=91 cm), 1.5 GHz (20 cm) and 10.6 GHz (2.8 cm), have been aligned, placed on a common grid, smoothed to common resolutions of 80" (=0.16 pc at 420 pc) and 90" (=0.18 pc) and compared on a position-by-position basis. The results are not consistent with a single value of Te. Rather, there is a significant variation, from Te =6000K in the low intensity, extended region to Te=8500K in the higher intensity, more compact region. The best fit to the data is a multi-layer model obtained from radio recombination line (RRL) data. An estimate of temperature fluctuations from the model yields t2=0.003. This is a factor of 10 lower than fluctuation values from optical O++ line data.