We present observations using the NOrthern Extended Millimetre Array (NOEMA) of CO and H2O emission lines, and the underlying dust continuum in two quasars at z∼6, i.e., P215-16 at z = 5.78 and J1429+5447 at z = 6.18. Notably, among all published CO SLEDs of quasars at z∼6, the two systems reveal the highest and the lowest CO level of excitation, respectively. Our radiative transfer modeling of the CO SLED of P215-16 suggests that the molecular gas heated by AGN could be a plausible origin for the high CO excitation. For J1429+5447, we obtain the first well-sampled CO SLED (from transitions from 2-1 to 10-9) of a radio-loud quasar at z≳6. Analysis of the CO SLED suggests that a single photo-dissociation region (PDR) component could explain the CO excitation in the radio-loud quasar J1429+5447. This work highlights the utility of the CO SLED in uncovering the ISM properties in these young quasar-starburst systems at the highest redshift. The diversity of the CO SLEDs reveals the complexities in gas conditions and excitation mechanisms at their early evolutionary stage.
@article{arxiv.2401.04590,
title = {Diverse molecular gas excitations in quasar host galaxies at z \sim 6},
author = {Jianan Li and Ran Wang and Antonio Pensabene and Fabian Walter and Bram P. Venemans and Roberto Decarli and Eduardo Bañados and Pierre Cox and Roberto Neri and Alain Omont and Zheng Cai and Yana Khusanova and Fuxiang Xu and Dominik Riechers and Jeff wagg and Yali Shao and Yuanqi Liu and Karl M. Menten and Qiong Li and Xiaohui Fan},
journal= {arXiv preprint arXiv:2401.04590},
year = {2024}
}