An ALMA [C II] Survey of 27 Quasars at z > 5.94

Abstract

We present a survey of the [C II] 158 μm line and underlying far-infrared (FIR) dust continuum emission in a sample of 27 z ≳ 6 quasars using the Atacama Large Millimeter Array (ALMA) at ~ 1^" resolution. The [C II] line was significantly detected (at 〉 5-σ) in 23 sources (85%). We find typical line luminosities of L_([C II]) = 10^(9-10), L_⊙, and an average line width of ~385 km s^(-1). The [C II]-to-far-infrared luminosity ratios ([C ii]/FIR) in our sources span one order of magnitude, highlighting a variety of conditions in the star-forming medium. Four quasar host galaxies are clearly resolved in their [C II] emission on a few kpc scales. Basic estimates of the dynamical masses of the host galaxies give masses between 2 × 10^(10) and 2 × 10^(11) M_⊙, i.e., more than an order of magnitude below what is expected from local scaling relations, given the available limits on the masses of the central black holes (〉3 x 10^8 M_⊙, assuming Eddington-limited accretion). In stacked ALMA [C II] spectra of individual sources in our sample, we find no evidence of a deviation from a single Gaussian profile. The quasar luminosity does not strongly correlate with either the [C II] luminosity or equivalent width. This survey (with typical on-source integration times of 8 minutes) showcases the unparalleled sensitivity of ALMA at millimeter wavelengths, and offers a unique reference sample for the study of the first massive galaxies in the universe.

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