RESOLVED MOLECULAR GAS IN A QUASAR HOST GALAXY AT REDSHIFT z = 6.42

摘要

We present high-resolution Very Large Array (VLA) observations of the molecular gas in the host galaxy of the highest redshift quasar currently known, SDSS J1148+5251 ( z = 6.42). Our VLA data of the CO (3-2) emission have a maximum resolution of 0.17″ x 0.13″ ( ≤ 1 kpc) and enable us to resolve the molecular gas emission both spatially and in terms of velocity. The molecular gas in J1148+5251 is extended to a radius of 2.5 kpc, and the central region shows two peaks separated by 0.3″ (1.7 kpc). These peaks account for about half of the total emission, while the remainder is more extended. Each of these unresolved peaks contains a molecular gas mass of ～5 x 10~9 solar mass (similar to the total mass found in nearby ultraluminous infrared galaxies) and has an intrinsic brightness temperature of ～35 K (averaged over the 1 kpc-sized beam), comparable to what is found in nearby starburst centers. Assuming that the molecular gas is gravitationally bound, we estimate a dynamical mass of ～4.5 x 10~(10) solar mass within a radius of 2.5 kpc (～5.5 x 10~(10) solar mass if corrected for a derived inclination of i～ 65°). This dynamical mass estimate leaves little room for matter other than the detected molecular gas; in particular, the data are inconsistent with a ～10~(12) solar mass stellar bulge that would be predicted based on the M_(BH)-σ_(bulge) relation. This finding may indicate that black holes form prior to the assembly of the stellar bulges and that the dark matter halos are less massive than those predicted on the basis of the black hole/bulge mass relationship.