No Evidence for [C ii] Halos or High-velocity Outflows in z ≳ 6 Quasar Host Galaxies

Abstract

We study the interstellar medium in a sample of 27 high-redshift quasar host galaxies at z ≳ 6, using the [C ii] 158 μm emission line and the underlying dust continuum observed at ∼1 kpc resolution with Atacama Large Millimeter Array. By performing uv-plane spectral stacking of both the high and low spatial resolution data, we investigate the spatial and velocity extent of gas and the size of the dust-emitting regions. We find that the average surface brightness profile of both the [C ii] and the dust continuum emission can be described by a steep component within a radius of 2 kpc and a shallower component with a scale length of 2 kpc, detected up to ∼10 kpc. The surface brightness of the extended emission drops below ∼1% of the peak at radius of ∼5 kpc, beyond which it constitutes 10%–20% of the total measured flux density. Although the central component of the dust continuum emission is more compact than that of the [C ii] emission, the extended components have equivalent profiles. The observed extended components are consistent with those predicted by hydrodynamical simulations of galaxies with similar infrared luminosities, where the dust emission is powered by star formation. The [C ii] spectrum measured in the mean uv-plane stacked data can be described by a single Gaussian, with no observable [C ii] broad-line emission (velocities in excess of ≳500 km s−1), which would be indicative of outflows. Our findings suggest that we are probing the interstellar medium and associated star formation in the quasar host galaxies up to radii of 10 kpc, whereas we find no evidence for halos or outflows.

ALMA Lensing Cluster Survey: Bright [C ii] 158 μm Lines from a Multiply Imaged Sub-L ⋆ Galaxy at z = 6.0719

“…The uncertainties of the SFR estimates might contribute to the large dispersion in high-z galaxies, due to assumptions regarding star formation history, the dust-attenuation curve, and the stellar population age, as discussed in Carniani et al (2020), andSchaerer et al (2020). Another recent report regarding the extended [C II] line morphology up to a radius of ∼10 kpc (e.g., Fujimoto et al 2019Fujimoto et al , 2020bGinolfi et al 2020;Novak et al 2020) might also be related to some of those nondetections, because the surface brightness of the extended emission is significantly decreased in relatively high-resolution maps (Carniani et al 2020). Based on visibility-based stacking, the secondary extended component up to the 10 kpc scale is estimated to have an average contribution to the total line luminosity of ∼50% around star-forming galaxies (Fujimoto et al 2019), and ∼20% around quasars (Novak et al 2020) at z ∼ 6.…”

“…Another recent report regarding the extended [C II] line morphology up to a radius of ∼10 kpc (e.g., Fujimoto et al 2019Fujimoto et al , 2020bGinolfi et al 2020;Novak et al 2020) might also be related to some of those nondetections, because the surface brightness of the extended emission is significantly decreased in relatively high-resolution maps (Carniani et al 2020). Based on visibility-based stacking, the secondary extended component up to the 10 kpc scale is estimated to have an average contribution to the total line luminosity of ∼50% around star-forming galaxies (Fujimoto et al 2019), and ∼20% around quasars (Novak et al 2020) at z ∼ 6. These non-negligible contributions may be significant if the request sensitivity is close to the detection limit around the 5σ level.…”

Geometry effects on dust attenuation curves with different grain sources at high redshift

“…Although the diversity of stellar mass among the The total optical depth varies with R. The spatial extent of dust emission is comparable to the resolution of ALMA (∼a few kpc; e.g. Fujimoto et al 2017;Hashimoto et al 2019;Novak et al 2020). We examine R = 5 kpc for a case of moderate extinction, and shrink it down to 0.5 kpc for a case where stars are heavily obscured.…”

The IRX–β relation of high-redshift galaxies

“…z 5) which was previously not possible with single-dish telescopes (e.g. Capak et al 2015;Watson et al 2015;Bouwens et al 2016Bouwens et al , 2020Walter et al 2016;Laporte et al 2017;Venemans et al 2017;Carniani et al 2018a;Bañados et al 2019;Jin et al 2019;Matthee et al 2019;Novak et al 2019Novak et al , 2020Bakx et al 2020;Faisst et al 2020;Neeleman et al 2020). To date, there have been a handful of objects at this epoch that have reported observational constraints on their IRX-β UV relation but with large scatter.…”