Star Formation and ISM Properties in the Host Galaxies of Three Far-infrared Luminous Quasars at z ∼ 6

Abstract

We present Karl G. Jansky Very Large Array observations of the CO (2-1) line emission toward three far-infrared luminous quasars at z ∼ 6: SDSS J231038.88+185519.7 and SDSS J012958.51-003539.7 with ∼0.″6 resolution and SDSS J205406.42-000514.8 with ∼2.″1 resolution. All three sources are detected in the CO (2-1) line emission—one source is marginally resolved, and the other two appear as point sources. Measurements of the CO (2-1) line emission allow us to calculate the molecular gas mass even without a CO excitation model. The inferred molecular gas masses are (0.8-4.3) × 10¹⁰ M _⊙. The widths and redshifts derived from the CO (2-1) line are consistent with previous CO (6-5) and [C II] measurements. We also report continuum measurements using Herschel for SDSS J231038.88+185519.7 and SDSS J012958.51-003539.7, and for SDSS J231038.88+185519.7 data obtained at ∼140 and ∼300 GHz using the Atacama Large Millimeter/submillimeter Array. In the case of SDSS J231038.88+185519.7, we present a detailed analysis of the spectral energy distribution and derive the dust temperature (∼40 K), the dust mass (∼10⁹ M _⊙), the far-infrared luminosity (8-1000 μm ∼10¹³ L _⊙), and the star formation rate (2400-2700 M _⊙ yr^-1). Finally, an analysis of the photodissociation regions associated with the three high-redshift quasars indicates that the interstellar medium in these sources has similar properties to local starburst galaxies.