CO(1-0) emission from quasar host galaxies beyond redshift 4

Molecular gas has now been detected in 15 z > 2 QSOs through observations of high-J CO transitions using millimeter interferometers. Observations of the GO ground-state transition CO(1-0), however, have the potential to trace the molecular gas at lower excitations, which may give a better estimate of the total molecular gas content of high-z QSOs. Here we present the first z > 4 CO(1-0) observations obtained with the NRAO Green Bank Telescope (GBT) and the MPIfR Effelsberg telescope. Utilizing the K band receivers of these two 100m radio telescopes, we detect the CO(1-0) transition in the high-redshift QSOs BR1202-0725 (z = 4.7)7 PSSJ2322+1944 (z = 4.1) and APM08279+5255 (z = 3.9). From LVG models based on our observations out to z = 4.7, we derive that the GO emission from all observed transitions can be described by a single gas component, and that all molecular gas appears to be concentrated in a compact nuclear region. The spectral capabilities of the GBT (1 x 200 MHz in high-resolution mode, 2 x 800 MHz in high-bandwidth mode) allow us to cover velocity ranges of up to 22, 000 km s-1, or Delta z/z = 0.09 at z = 4, which will be imperative for future high-z studies in galaxies with known strong dust continuum but poorly constrained redshift. This is a first step towards observations with future z-machines.