CO (2-1) Line Emission in Redshift 6 Quasar Host Galaxies

TL;DR

This study reports new CO (2-1) line emission observations in five z~6 quasars, revealing insights into gas excitation, galaxy mergers, and star formation in the early universe's most distant quasar host galaxies.

Contribution

First detection of CO (2-1) emission in high-redshift quasars, providing constraints on gas excitation and evidence of galaxy mergers at z~6.

Findings

CO (2-1) detected in two quasars, one marginal detection

Resolved CO emission indicates a possible galaxy merger

Supports coeval star formation and black hole growth in early universe

Abstract

We report new observations of CO (2-1) line emission toward five z~6 quasars using the Ka-band receiver system on the Expanded Very Large Array (EVLA). Strong detections were obtained in two of them, SDSS J092721.82+200123.7 and CFHQS J142952.17+544717.6, and a marginal detection was obtained in another source, SDSS J084035.09+562419.9. Upper limits of the CO (2-1) line emission have been obtained for the other two objects. The CO (2-1) line detection in J0927+2001, together with previous measurements of the CO (6-5) and (5-4) lines, reveals important constraints on the CO excitation in the central ~10 kpc region of the quasar host galaxy. The CO (2-1) line emission from J1429+5447 is resolved into two distinct peaks separated by 1.2" (~6.9 kpc), indicating a possible gas-rich, major merging system, and the optical quasar position is consistent with the west peak. This result is in good agreement with the picture in which intense host galaxy star formation is coeval with rapid supermassive black hole accretion in the most distant universe. The two EVLA detections are ideal targets for further high-resolution imaging (e.g., with ALMA or EVLA observations) to study the gas distribution, dynamics, and SMBH-bulge mass relation in these earliest quasar-host galaxy systems.