Yi-Han Wu (National Tsing Hua University); Tomotsugu Goto (National Tsing Hua University)
Does the dark energy vary at different cosmic epochs ? To answer this question, we need to map the expansion feature over a large span of the cosmic time. Type Ia supernovae have been a reliable indicator to measure distances to redshift (z) of 2, but beyond this, no reliable distance measure has been established. A new distance measurement using sub-millimeter (submm) galaxies (z ~ 6) has been proposed. Utilizing a large sample of submm galaxies (1 < z < 6) in literature, we present the existence of a significant correlation between the CO luminosity and the CO line width (FWHM). Through the distance calibration, we can use the calibrated correlation to measure the luminosity distances of the submm galaxies based on their observed FWHMs, and establish the Hubble Diagram to z ~ 6. Thanks to the advance of the ALMA, a large numbers of more distant (z > 6) submm galaxies are observed in other molecular emissions, and the relevant correlation are still in investigation. This suitable and feasible method is presented for such an era, providing a new opportunity to constrain the earliest cosmic expansion.