CO( J = 1→0) IN z > 2 QUASAR HOST GALAXIES: NO EVIDENCE FOR EXTENDED MOLECULAR GAS RESERVOIRS

Abstract

We report the detection of CO( J = 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( J = 1→0) line luminosities of L ' CO = (0.34–18.4) × 10 10 K km s −1 pc 2 and total molecular gas masses of M (H 2 ) = (0.27–14.7) × 10 10 M ☉ 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( J = 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( J = 1→0) observations. These findings stand in contrast to recent CO( J = 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.