CO and Dust in PSS 2322+1944 at a redshift of 4.12

Abstract

Using the IRAM interferometer we have detected J = 4 → 3 and 5 → 4 CO line emission toward the radio quiet quasar PSS 2322+1944. At a redshift of z_(CO) = 4.1199 this is the fourth and strongest detection of CO at z > 4. The velocity-integrated CO J = 4 → 3 and J = 5 → 4 line fluxes are 4.21 ± 0.40 and 3.74 ± 0.56 Jy km s^(-1), and the linewidth is ≈ 300 km s^(-1). The CO J = 10 → 9 was searched for but not detected with an upper intensity limit of 30 mJy. The 1.35 mm (250 µm rest wavelength) continuum flux density is 7.5 ± 1.3 mJy, in agreement with previous bolometer measurements at 1.2 mm with the 30-m IRAM telescope. The 3 mm (580 µm rest wavelength) continuum is not detected with a 3 σ upper limit of 0.7 mJy. We also report observations of the 450 µm continuum in PSS 2322+1944 using the SCUBA array at the JCMT. The quasar was detected with a 450 µm flux density of 79 ± 19 mJy. At the angular resolution of 4."8 x 2." at 1.3 mm and 6."2 x 4."9 at 3.2 mm, the interferometer observations do not show evidence of spatial extension in the continuum or CO line emission. Assuming no gravitational magnification, we estimate a molecular gas mass of ≈ 2.5 x 10^(11) M_☉. The molecular gas is warm (40-100K) and dense (10^(3.5) 10^(4.1) cm^(-3). The infrared-to-CO luminosity ratio is ≈185 L_☉ (K km-s^(-1) pc^2)^(-1), comparable to the values found for ultraluminous infrared galaxies. The detection of CO emission in this high redshift QSO provides further evidence that the radio emission and the millimeter to submillimeter continuum emission are predominantly powered by a starburst which is coeval with the AGN activity.

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