A Multi-Scale Study of Star Formation in Messier 33

• Published in: arXiv.org 2018-11
• Main Authors: Elson, E C, Kam, S Z, Chemin, L, Carignan, C, Jarrett, T H
• Format: Article
• Language: English
• Subjects: Astronomical models; Data smoothing; Emission; Galaxies; Local group (astronomy); Multiscale analysis; Neutral gases; Star & galaxy formation; Star formation rate
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1811.04590

For the Local Group Scd galaxy M 33 this paper presents a multi-scale study of the relationship between the monochromatic star formation rate (SFR) estimator based on 12 \(\mu\)m emission and the total SFR estimator based on a combination of far-ultraviolet and 24 \(\mu\)m emission. We show the 12 \(\mu\)m emission to be a linear estimator of total SFR on spatial scales from 782 pc down to 49 pc, over almost four magnitudes in SFR. These results therefore extend to sub-kpc length scales the analogous results from other studies for global length scales. We use high-resolution HI and \(^{12}\mathrm{CO}(J=2-1)\) image sets from the literature to compare the star formation to the neutral gas. For the full range of length scales we find well-defined power-law relationships between 12 \(\mu\)m-derived SFR surface densities and neutral gas surface densities. For the H\(_\mathrm{2}\) gas component almost all correlations are consistent with being linear. No evidence is found for a breakdown in the star formation law at small length scales in M 33 reported by other authors. We show that the average star formation efficiency in M 33 is roughly \(10^{-9}\) yr\(^{-1}\) and that it remains constant down to giant molecular cloud length scales. Toomre and shear-based models of the star formation threshold are shown to inaccurately account for the star formation activity in the inner disc of M 33. Finally, we clearly show that the HI saturation limit of \(\approx 9\) M\(_{\odot}\) pc\(^{-2}\) reported in the literature for other galaxies is not an intrinsic property of M 33 - it is systematically introduced as an artefact of spatially smoothing the data.