DOWSING, dust observations with SCUBA-2 in nearby galaxies: I. Dust in M 81

Uzuner, M. ORCID: https://orcid.org/0000-0002-4387-7684, Smith, M. W. L. ORCID: https://orcid.org/0000-0002-3532-6970, Eales, S. ORCID: https://orcid.org/0000-0002-7394-426X, Chung, A., Chung, E. J., Clements, D. L., de Looze, I., Eden, D. J., Fanciullo, L., Ho, L. C., Kemper, F., Pattle, K., Relaño, M., Saintonge, A., Tang, X., Van Der Giessen, S. A., Wang, J., Williams, T. G. and Wilson, C. D. 2026. DOWSING, dust observations with SCUBA-2 in nearby galaxies: I. Dust in M 81. Monthly Notices of the Royal Astronomical Society , stag2127. 10.1093/mnras/stag2127

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Abstract

We present a resolved far-infrared/sub-millimetre study of dust in the nearby spiral galaxy M 81 using Herschel PACS/SPIRE and JCMT SCUBA-2 observations from 70 to 850 μm. We model the dust emission using both single-temperature modified blackbody (SMBB) fits and point process mapping (PPMAP), comparing pixel-by-pixel SED-fitting with image cubes of dust surface density as a function of position and temperature. For fixed β = 1.9 and a dust opacity of κ350μm = 1.92 cm2 g−1, SMBB gives an integrated dust mass of (1.77 ± 0.09) × 107M⊙, while PPMAP gives (2.65 ± 0.13) × 107M⊙. The higher PPMAP mass is expected because real lines of sight contain dust over a range of temperatures, whereas SMBB assumes a single effective temperature and can underestimate the dust mass. Both methods show enhanced dust surface densities along the spiral arms and a radially declining dust temperature, with the warmest dust in the central region. Variable-β fits indicate only moderate spatial variation in β for well-constrained pixels, but the strong T–β degeneracy motivates a fixed emissivity index for the main analysis. Combining the dust maps with H i data, we find a positive radial gas-to-dust ratio gradient, with dlog10(GDR)/dR = 0.065 dex kpc−1. Comparison with M 81’s metallicity gradient implies a declining dust-to-metals ratio, potentially consistent with more efficient grain growth in the inner disc. The star formation rate is modest, ~0.27 M⊙ yr−1, and is strongly concentrated along the spiral arms. These results suggest that the dust, gas, and star-forming structures of M 81 are strongly shaped by its spiral arms, while the central region hosts the warmest dust in the disc.

Item Type:	Article
Date Type:	Published Online
Status:	In Press
Schools:	Schools > Physical, Chemical & Environmental Sciences Schools > Physics and Astronomy
Publisher:	Oxford University Press
ISSN:	0035-8711
Date of First Compliant Deposit:	13 November 2026
Last Modified:	13 Nov 2026 11:18
URI:	https://orca.cardiff.ac.uk/id/eprint/190895

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