A spatially resolved radio spectral index study of the dwarf irregular galaxy NGC 1569. Issue 4 (11th January 2018)

• Record Type: Journal Article
• Authors: Westcott, Jonathan; Brinks, Elias; Hindson, Luke; Beswick, Robert; Heesen, Volker
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 475:Issue 4(2018)
• Page Start: 5116
• Page End: 5132
• Publication Date: 2018-01-11
• Subjects: methods: data analysis -- techniques: interferometric -- cosmic rays -- H ii regions -- ISM: magnetic fields -- radio continuum: galaxies; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/sty028
• Languages: English
• ISSNs: 0035-8711

Abstract

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 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 disc. We find a higher thermal fraction at 1 GHz than is found in spiral galaxies ($26^{+2}_{-3}\, {per\, cent}$ ) and find an average non-thermal spectral index α = −0.53 ± 0.02, 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 ± 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.