ALMA observations of 99 GHz free-free and H40$\alpha$ line emission from star formation in the centre of NGC 253

Abstract

We present Atacama Large Millimeter/submillimeter Array observations of 99.02 GHz free-free and H40$\alpha$ emission from the centre of the nearby starburst galaxy NGC 253. We calculate electron temperatures of 3700-4500 K for the photoionized gas, which agrees with previous measurements. We measure a photoionizing photon production rate of $(3.2\pm 0.2)\times 10^{53}$ s${}^{-1}$ and a star formation rate of $1.73\pm 0.12$ M${}_{\odot }$ yr${}^{-1}$ within the central 20$\times$10 arcsec, which fall within the broad range of measurements from previous millimetre and radio observations but which are better constrained. We also demonstrate that the dust opacities are ~3 dex higher than inferred from previous near-infrared data, which illustrates the benefits of using millimetre star formation tracers in very dusty sources.

5 pages, 3 figures, accepted for publication in MNRAS Letters

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• The ACS Nearby Galaxy Survey Treasury
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