ALMA and JWST Imaging of $z\ >\ 6$ Quasars: No Spatial Position Offset Observed Between Quasars and Their Host Galaxies

TL;DR

This study uses high-resolution ALMA imaging of [CII] 158 μm and dust continuum together with JWST NIRCam astrometry tied to GAIA to search for spatial offsets between the centers of six z > 6 quasars and their host galaxies. The authors perform precise astrometric comparisons and conduct kinematic modeling with a thin-disk approach to characterize host dynamics. They find that all quasars reside near the centers of their host galaxies on ~400 pc scales, and no robust SMBH–host offsets are detected; rest-frame optical offsets reported in some JWST studies are likely due to dust obscuration rather than real displacements. The results support theoretical expectations that recoil events at high redshift are rare or short-lived and demonstrate the power of combining JWST and ALMA data to constrain SMBH–galaxy coevolution at early cosmic times.

Abstract

We present a study determining the spatial offset between the position of the supermassive black hole (as traced through their broad line regions) and the host galaxy in six $z > 6$ quasars. We determined the host galaxy's position from $\lesssim$$0.1^{\prime\prime}$ ($\lesssim$ 600 pc) resolution Atacama Large Millimeter/sub-millimeter Array (ALMA) [CII] 158 $μm$ and corresponding dust continuum imaging. We determined the quasar's position from $\lesssim$ 400 pc resolution James Webb Space Telescope Near-Infrared Camera (JWST NIRCam) imaging. We estimated the observational uncertainties on the quasar's position using astrometric data from the Global Astrometric Interferometer for Astrophysics (GAIA) of field stars within the NIRCam images. We find that all six quasars are found within the central $\sim 400$ pc of their host galaxy dust continuum and [CII] emission. Apparent offsets seen in rest-frame optical JWST observations are not detected in our ALMA data, suggesting they likely result from dust obscuration rather than a true physical separation between the SMBH and its host galaxy. Kinematic modeling of these data further reveals that none of the galaxies show evidence for recent merger activity, and most of the galaxies can be accurately modeled using a simple disk model. The lack of an offset supports theoretical models that predict that positional offset within these galaxies are either short-lived or intrinsically rare.

Figures (14)

• Figure 1: J2054$-$0005 continuum, [C2] velocity-integrated flux density, mean velocity, and velocity dispersion maps. The cross marks the position of the quasar within the galaxy with error bars as found by comparing JWST and GAIA data (detailed in Section \ref{['subsec:astrometry']}). The contours in the top two panels start at 2$\sigma$ and increase by powers of $\sqrt{2}$. The synthesized beam is shown in the bottom left corner of each panel.
• Figure 2: JWST NIRCam images of each source in our sample, shown in the filter used for GAIA comparison and coordinate measurements (see Table \ref{['tab:jwst']}). The axes are centered on the measured position of each source.
• Figure 3: Continuum imaging of all six sources in the sample. Previous optical position of the quasars are noted in red. JWST positions (see Section \ref{['sec:jwst']}) of the quasars are shown in white. For sources lacking reported uncertainties in the literature for their previous coordinates, the positions are marked with a dot. We note that the spatial scaling for J0109$-$3047 is different, for the clearest possible view of the galaxy. Contours and annotations are similar to Figure \ref{['fig:4pan 2054']}.
• Figure 4: [C2] imaging of all six sources in the sample. Contours and annotations are similar to Figure \ref{['fig:cont 6pan']}.
• Figure 5: J2054$-$0005 Channel Maps from the qubefit thin disk model. The left panel shows [C2] data at each 30 km s$^{-1}$ increment with contours of the model. The right panel shows [C2] emission at each 30 km s$^{-1}$ increment with residual contours. Both sets of contours start at $2 \sigma$ and increase by factors of $\sqrt{2}$.