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arXiv · 1712.00025

A Spatially Resolved Radio Spectral Index Study of the Dwarf Irregular Galaxy NGC\,1569

Jonathan Westcott·Elias Brinks·Luke Hindson·Robert Beswick·Volker Heesen
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Abstract

We study the resolved radio-continuum spectral energy distribution of the dwarf irregular galaxy, NGC 1569, on a beam-by-beam basis to isolate and study its spatially resolved radio emission characteristics. Utilizing high quality NRAO Karl G. Jansky Very Large Array (VLA) observations that densely sample the 1--34\,GHz frequency range, we adopt a Bayesian fitting procedure, where we use H$α$ emission that has not been corrected for extinction as a prior, to produce maps of how the separated thermal emission, non-thermal emission and non-thermal spectral index vary across NGC\,1569's main disk. We find a higher thermal fraction at 1\,GHz than is found in spiral galaxies ($26^{+2}_{-3}\%$) and find an average non-thermal spectral index $α= -0.53\pm0.02$, suggesting that a young population of cosmic ray electrons is responsible for the observed non--thermal emission. By comparing our recovered map of the thermal radio emission with literature H$α$ maps, we estimate the total reddening along the line of sight to NGC\,1569 to be $E(B-V) = 0.49 \pm 0.05$, which is in good agreement with other literature measurements. Spatial variations in the reddening indicate that a significant portion of the total reddening is due to internal extinction within NGC\,1569.

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Jonathan Westcott, Elias Brinks, Luke Hindson, Robert Beswick, Volker Heesen. 2017-11-30. A Spatially Resolved Radio Spectral Index Study of the Dwarf Irregular Galaxy NGC\,1569. https://doi.org/10.1093/mnras%2Fsty028

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