Pushing the Atacama Large Millimeter/submillimeter Array to the Limit: 140 pc Resolution Observations of a z = 6.6 Quasar–Galaxy Merger Resolve Strikingly Different Morphologies of Dust Continuum and [C ii] 158 μm Emission
We present $0\mathop{.}\limits^{^{\prime\prime} }026$ (140 pc) resolution Atacama Large Millimeter/submillimeter Array observations of [C ii ] 158 μ m and dust continuum emission of the z = 6.6 quasar J0305–3150, resolved over ~300–400 independent resolution elements. The dust continuum emissi...
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| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
IOP Publishing
2025-01-01
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| Series: | The Astrophysical Journal |
| Subjects: | |
| Online Access: | https://doi.org/10.3847/1538-4357/ada351 |
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| Summary: | We present $0\mathop{.}\limits^{^{\prime\prime} }026$ (140 pc) resolution Atacama Large Millimeter/submillimeter Array observations of [C ii ] 158 μ m and dust continuum emission of the z = 6.6 quasar J0305–3150, resolved over ~300–400 independent resolution elements. The dust continuum emission is compact with ~80% recovered within $r\lt 0\mathop{.}\limits^{^{\prime\prime} }3$ (1.6 kpc), whereas the [C ii ] emission profile is composed of a central Gaussian ( $r\lt 0\mathop{.}\limits^{^{\prime\prime} }4$ , i.e., <2.2 kpc) and an extended component (detected up to ~10 kpc at >3 σ ). We infer a direct contribution of the quasar to the observed 260 GHz continuum S _ν _,QSO / S _ν _,QSO + Host ≲ 1%. We report the detection of far-infrared (FIR)-detected star-forming clumps with r < 200 pc and properties similar to that of rest-frame UV–optical clumps reported in the literature. The 200 pc resolved [C ii ]/FIR ratio follows the global relation with the FIR surface brightness established in low- and high-redshift galaxies, even at the quasar location. We find that dust continuum is emitted in regions of $\unicode{x0007E}0^{\prime\prime} \,.02-0^{\prime\prime} \,.04$ consistent with the size of photodissociation regions (PDRs), whereas 50% of the [C ii ] originates from larger physical scales ( θ ≳ 2″). The large-scale [C ii ] emission presents a velocity gradient aligned with a nearby companion with perturbed kinematics, and misaligned with the kinematics of the small-scale emission. The absence of significant [C ii ] emission by structures with physical scale ≲ 1 kpc implies that [C ii ] emission is not produced in dense PDRs located at the boundary of giant molecular clouds. We argue instead that [C ii ] is produced in low-density PDRs in the interstellar medium and diffuse H i gas tidally stripped during the ongoing merger. |
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| ISSN: | 1538-4357 |