On the millimetre continuum flux-radius correlation of proto-planetary discs. (arXiv:1905.00021v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Rosotti_G/0/1/0/all/0/1">Giovanni P. Rosotti</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Booth_R/0/1/0/all/0/1">Richard A. Booth</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Tazzari_M/0/1/0/all/0/1">Marco Tazzari</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Clarke_C/0/1/0/all/0/1">Cathie Clarke</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lodato_G/0/1/0/all/0/1">Giuseppe Lodato</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Testi_L/0/1/0/all/0/1">Leonardo Testi</a>
A correlation between proto-planetary disc radii and sub-mm fluxes has been
recently reported. In this Letter we show that the correlation is a sensitive
probe of grain growth processes. Using models of grain growth and drift, we
have shown in a companion paper that the observed disc radii trace where the
dust grains are large enough to have a significant sub-mm opacity. We show that
the observed correlation emerges naturally if the maximum grain size is set by
radial drift, implying relatively low values of the viscous $alpha$ parameter
$ lesssim 0.001$. In this case the relation has an almost universal
normalisation, while if the grain size is set by fragmentation the flux at a
given radius depends on the dust-to-gas ratio. We highlight two observational
consequences of the fact that radial drift limits the grain size. The first is
that the dust masses measured from the sub-mm could be overestimated by a
factor of a few. The second is that the correlation should be present also at
longer wavelengths (e.g. 3mm), with a normalisation factor that scales as the
square of the observing frequency as in the optically thick case.
A correlation between proto-planetary disc radii and sub-mm fluxes has been
recently reported. In this Letter we show that the correlation is a sensitive
probe of grain growth processes. Using models of grain growth and drift, we
have shown in a companion paper that the observed disc radii trace where the
dust grains are large enough to have a significant sub-mm opacity. We show that
the observed correlation emerges naturally if the maximum grain size is set by
radial drift, implying relatively low values of the viscous $alpha$ parameter
$ lesssim 0.001$. In this case the relation has an almost universal
normalisation, while if the grain size is set by fragmentation the flux at a
given radius depends on the dust-to-gas ratio. We highlight two observational
consequences of the fact that radial drift limits the grain size. The first is
that the dust masses measured from the sub-mm could be overestimated by a
factor of a few. The second is that the correlation should be present also at
longer wavelengths (e.g. 3mm), with a normalisation factor that scales as the
square of the observing frequency as in the optically thick case.
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