Abstract

In the age of ALMA images of dust continuum and carbon monoxide (CO) line emission are our new and powerful tools for deducing structural characteristics of early galaxies such as disc scalelengths, H2 gas velocity fields and enclosed H2 and dynamical masses. Such images are also used to deduce the Toomre Q parameter of gas-rich disks at high redshifts, an important parameter for deciding how star-formation is driven in these extreme objects. The rising Cosmic Microwave Background (CMB) places a fundamental constraint on the structural information that can be deduced from such images, progressively erasing all spatial and spectral contrasts between their brightness distributions and the CMB . This limitation is unique to millimetre/submillimetre wavelengths and unlike its known effect on the global dust continuum and molecular line emission of galaxies, it cannot be addressed simply. We have found two possible ways around it that will be discussed in some detail.