CO(1-0) in z>2 Quasar Host Galaxies: No Evidence for Extended Molecular Gas Reservoirs

TL;DR

This study detects CO(1-0) emission in high-redshift quasar host galaxies, finding no evidence for extended low-excitation molecular gas reservoirs, and suggests different evolutionary stages for quasars and submillimeter galaxies.

Contribution

First systematic CO(1-0) observations of z>2 quasars showing they lack extended low-excitation gas reservoirs, contrasting with SMGs.

Findings

CO(1-0) line strengths are consistent with single, highly-excited gas components.

No evidence for luminous extended low-excitation molecular gas.

Quasars and SMGs likely represent different stages in galaxy evolution.

Abstract

We report the detection of CO(1-0) emission in the strongly lensed high-redshift quasars IRAS F10214+4724 (z=2.286), the Cloverleaf (z=2.558), RX J0911+0551 (z=2.796), SMM J04135+10277 (z=2.846), and MG 0751+2716 (z=3.200), using the Expanded Very Large Array and the Green Bank Telescope. We report lensing-corrected CO(1-0) line luminosities of L'(CO) = 0.34-18.4 x 10^10 K km/s pc^2 and total molecular gas masses of M(H2) = 0.27-14.7 x 10^10 Msun for the sources in our sample. Based on CO line ratios relative to previously reported observations in J>=3 rotational transitions and line excitation modeling, we find that the CO(1-0) line strengths in our targets are consistent with single, highly-excited gas components with constant brightness temperature up to mid-J levels. We thus do not find any evidence for luminous extended, low excitation, low surface brightness molecular gas components. These properties are comparable to those found in z>4 quasars with existing CO(1-0) observations. These findings stand in contrast to recent CO(1-0) observations of z~2-4 submillimeter galaxies (SMGs), which have lower CO excitation and show evidence for multiple excitation components, including some low-excitation gas. These findings are consistent with the picture that gas-rich quasars and SMGs represent different stages in the early evolution of massive galaxies.