The test of correlation of CO Luminosity and line width.
Yi-han Wu1*, Tomotsugu Goto1
1Institute of Astronomy, National Tsing Hua University, HsinChu, Taiwan
* presenting author:Han Han,
The nature of dark energy remains unknown. Especially, we do not know if it varies with time. To constrain the dark-energy equation of the state parameter, w(z), especially its time dependence, it is necessary to observe the Universe at higher redshift by breaking the degeneracies between cosmological models (Linder & Huterer 2003,King et al.2014). Previously, Goto proposed a new measurement for distance as using sub-millimeter (submm) galaxies. Using a large sample of submm galaxies compiled from the literature, they showed there exists a significant correlation between the CO luminosity (L'CO) and the line width (FWHM) of submm galaxies. They used this correlation to measure intrinsic luminosity of submm galaxies, based on the observed FWHM. By comparing with observed brightness, they measured luminosity distances to these galaxies, and constructed the Hubble diagram to z~6. However, this method can not be used if the relation above is as function of redshift. Hence, we compile a large sample of CO galaxies to test lower redshift dependence.

Keywords: SMGs , QSOs, CO luminosity, Cosmology, Line width