The relationship between dust and [CI] at z=1 and beyond
  Measuring molecular gas mass is vital for understanding the evolution of
galaxies at high redshifts (z$\geq$1). Most measurements rely on CO as a
tracer, but dependences on metallicity, dynamics and surface density lead to
systematic uncertainties in high-z galaxies, where these physical properties
are difficult to observe, and where the physical environments can differ
systematically from those at z=0. Dust continuum emission provides a potential
alternative assuming a known dust/gas ratio, but this must be calibrated on a
direct gas tracer at z$\geq$1. In this paper we consider the [CI] 492-GHz
emission line, which has been shown to trace molecular gas closely throughout
Galactic clouds and has the advantages of being optically thin in typical
conditions (unlike CO), and being observable at accessible frequencies at high
redshifts (in contrast to the low-excitation lines of CO). We use the Atacama
Large Millimetre/submillimetre Array (ALMA) to measure [CI], CO(4-3) and dust
emission in a representative sample of star-forming galaxies at z=1, and
combine these data with multi-wavelength spectral energy distributions to study
relationships between dust and gas components of galaxies. We uncover a strong
[CI]-dust correlation, suggesting that both trace similar phases of the gas. By
incorporating other samples from the literature, we show that this correlation
persists over a wide range of luminosities and redshifts up to z$\sim$4.
Finally we explore the implications of our results as an independent test of
literature calibrations for dust as a tracer of gas mass, and for predicting
the CI abundance.
