We present 0 . 3 (band 6) and 1 . 5 (band 3) ALMA observations of the (sub)millimeter dust continuum emission for 25 radio galaxies at 1 < z < 5.2. Our survey reaches a rms flux density of ∼50 µJy in band 6 (200-250 GHz) and ∼20 µJy in band 3 (100-130 GHz). This is an order of magnitude deeper than single-dish 850 µm observations, and reaches fluxes where synchrotron and thermal dust emission are expected to be of the same order of magnitude. Combining our sensitive ALMA observations with low-resolution radio data from ATCA, higher resolution VLA data, and infrared photometry from Herschel and Spitzer, we have disentangled the synchrotron and thermal dust emission. We determine the star-formation rates and AGN infrared luminosities using our newly developed Multiresolution and multi-object/origin spectral energy distribution fitting code (Mr-Moose). We find that synchrotron emission contributes substantially at λ ∼1 mm. Through our sensitive flux limits and accounting for a contribution from synchrotron emission in the mm, we revise downward the median star-formation rate by a factor of seven compared to previous estimates based solely on Herschel and Spitzer data. The hosts of these radio-loud AGN appear predominantly below the main sequence of star-forming galaxies, indicating that the star formation in many of the host galaxies has been quenched. Future growth of the host galaxies without substantial black hole mass growth will be needed to bring these objects on the local relation between the supermassive black holes and their host galaxies. Given the mismatch in the timescales of any star formation that took place in the host galaxies and lifetime of the AGN, we hypothesize that a key role is played by star formation in depleting the gas before the action of the powerful radio jets quickly drives out the remaining gas. This positive feedback loop of efficient star formation rapidly consuming the gas coupled to the action of the radio jets in removing the residual gas is how massive galaxies are rapidly quenched.

We have used the Multi-Unit Spectroscopic Explorer (MUSE) to study the circumgalactic medium (CGM) of a z = 2.92 radio galaxy, MRC 0943-242 by parametrising its emitting and absorbing gas. In both Lyα λ1216 and He ii λ1640 lines, we observe emission with velocity shifts of ∆ −1000 km s −1 from the systemic redshift of the galaxy. These blueshifted components represent kinematically perturbed gas that is aligned with the radio axis, which we interpret as jet-driven outflows. Three of the four known Lyα absorbers are detected at the same velocity as C iv λλ1548, 1551 and N v λλ1239, 1243 absorbers, proving that the gas is metal enriched more so than previously thought. At the velocity of a strong Lyα absorber with an H i column of N H i /cm −2 = 10 19.2 and velocity shift of ∆ −400 km s −1 , we also detect Si ii λ1260 and Si ii λ1527 absorption, which suggests that the absorbing gas is ionisation bounded. With the added sensitivity of this MUSE observation, we are more capable of adding constraints to absorber column densities and consequently determining what powers their ionisation. To do this, we obtain photoionisation grid models in cloudy which show that AGN radiation is capable of ionising the gas and producing the observed column densities in a gas of metallicity of Z/Z 0.01 with a nitrogen abundance a factor of 10 greater than that of hydrogen. This metal-enriched absorbing gas, which is also spatially extended over a projected distance of r 60 kpc, is likely to have undergone chemical enrichment through stellar winds that have swept up metals from the interstellar-medium and deposited them in the outer regions of the galaxy's halo.

Using MUSE on the ESO-VLT, we obtained a four-hour exposure of the z = 3.12 radio galaxy MRC 0316-257. We detect features down to ∼10 −19 erg s −1 cm −2 arcsec −2 , with the highest surface brightness regions reaching more than a factor of 100 higher. We find Lyα emission out to ∼250 kpc in projection from the active galactic nucleus (AGN). The emission shows arc-like morphologies arising at 150−250 kpc from the nucleus in projection, with the connected filamentary structures reaching down into the circumnuclear region. The most distant arc is offset by ∼700 km s −1 relative to circumnuclear HeIIλ1640 emission, which we assume to be at the systemic velocity. As we probe emission closer to the nucleus, the filamentary emission narrows in projection on the sky, the relative velocity decreases to ∼250 km s −1 , and the line full-width at half maximum ranges from ∼300−700 km s −1 . From UV line ratios, the emission on scales of 10s of kpc from the nucleus along a wide angle in the direction of the radio jets is clearly excited by the radio jets and ionizing radiation of the AGN. Assuming ionization equilibrium, the more extended emission outside of the axis of the jet direction would require 100% or more illumination to explain the observed surface brightness. High-speed ( 300 km s −1 ) shocks into rare gas would provide sufficiently high surface brightness. We discuss the possibility that the arcs of Lyα emission represent accretion shocks and the filamentary emission represents gas flows into the halo, and compare our results with gas accretion simulations.

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The MIGHTEE large survey project will survey four of the most well-studied extragalactic deep fields, totalling 20 square degrees to µJy sensitivity at Giga-Hertz frequencies, as well as an ultra-deep image of a single ∼1 deg 2 MeerKAT pointing. The observations will provide radio continuum, spectral line and polarisation information. As such, MIGHTEE, along with the excellent multi-wavelength data already available in these deep fields, will allow a range of science to be achieved. Specifically, MIGHTEE is designed to significantly enhance our understanding of, (i) the evolution of AGN and star-formation activity over cosmic time, as a function of stellar mass and environment, free of dust obscuration; (ii) the evolution of neutral hydrogen in the Universe and how this neutral gas eventually turns into stars after moving through the molecular phase, and how efficiently this can fuel AGN activity; (iii) the properties of cosmic magnetic fields and how they evolve in clusters, filaments and galaxies. MIGHTEE will reach similar depth to the planned SKA all-sky survey, and thus will provide a pilot to the cosmology experiments that will be carried out by the SKA over a much larger survey volume.