A radiative transfer model for the spiral galaxy M33

Thirlwall, Jordan Joe orcid iconORCID: 0000-0003-0390-8199, Popescu, Cristina orcid iconORCID: 0000-0002-7866-702X, Tuffs, Richard J., Natale, Giovanni, Norris, Mark orcid iconORCID: 0000-0002-7001-805X, Rushton, Mark, Grootes, Meiert and Carroll, Benjamin Timothy orcid iconORCID: 0000-0001-5267-2624 (2020) A radiative transfer model for the spiral galaxy M33. Monthly Notices of the Royal Astronomical Society, 495 (1). pp. 835-863. ISSN 0035-8711

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Official URL: https://doi.org/10.1093/mnras/staa905


We present the first radiative transfer (RT) model of a non-edge-on disk galaxy in which the large-scale geometry of stars and dust is self-consistently derived through fitting of multiwavelength imaging observations from the UV to the submm. To this end we used the axi-symmetric RT model of Popescu et al. and a new methodology for deriving geometrical parameters, and applied this to decode the{spectral energy distribution (SED) of M33. We successfully account for both the spatial and spectral energy distribution, with residuals typically within 7% in the profiles of surface brightness and within 8% in the spatially-integrated SED. We predict well the energy balance between absorption and re-emission by dust, with no need to invoke modified grain properties, and we find no submm emission that is in excess of our model predictions. We calculate that 80±8% of the dust heating is powered by the young stellar populations. We identify several morphological components in M33, a nuclear, an inner, a main and an outer disc, showing a monotonic trend in decreasing star-formation surface-density (ΣSFR) from the nuclear to the outer disc. In relation to surface density of stellar mass, the ΣSFR of these components define a steeper relation than the "main sequence" of star-forming galaxies, which we call a "structurally resolved main sequence". Either environmental or stellar feedback mechanisms could explain the slope of the newly defined sequence. We find the star-formation rate to be SFR=0.28+0.02−0.01M⊙yr−1.

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