We present the results of the kinematic study of the extended gas in a sample of 10 high‐redshift radio galaxies (z∼ 2.5) based on high signal‐to‐noise ratio Keck II and Very Large Telescope (VLT) long‐slit spectroscopy. In addition to the typical high surface brightness kinematically perturbed regions (FWHM and velocity shifts >1000 km s−1), we find in all objects giant low surface brightness haloes that show quieter kinematics with typical emission‐line FWHM and velocity shifts of ∼several hundred km s−1. The giant haloes often extend for more than 100 kpc and sometimes beyond the radio structures. They emit lines other than Lyα (C iv, He ii and N v in some cases), typically found in the spectra of high‐redshift active galaxies. Continuum is also often detected. The haloes are enriched with heavy elements at tens of kpc from the active nucleus. Typical Lyα luminosities and surface brightness (within the slit) are in the range 1043−44 erg s−1 and several × 10−17 to −16 erg cm−2 s−1 arcsec−2, respectively. Estimated densities are in the range ∼17–150 cm−3. The quasar continuum is the dominant source of ionization of the quiescent haloes along the radio axis. The implied total quasar ionizing luminosities are in the range ∼several × 1045–1047 erg s−1, in the same range as radio‐loud quasars at comparable redshift. The detection of giant quiescent haloes in all objects suggests that they could be a common ingredient of high‐redshift radio galaxies. The radio galaxies seem to be embedded within the haloes. The nature and the origin of the haloes, together with the cosmological implications, are also discussed.

The largest galaxies in the Universe reside in galaxy clusters. Using sensitive observations of carbon-monoxide, we show that the Spiderweb Galaxy -a massive galaxy in a distant proto-cluster -is forming from a large reservoir of molecular gas. Most of this molecular gas lies between the proto-cluster galaxies and has low velocity dispersion, indicating that it is part of an enriched inter-galactic medium. This may constitute the reservoir of gas that fuels the widespread star formation seen in earlier ultraviolet observations of the Spiderweb Galaxy. Our results support the notion that giant galaxies in clusters formed from extended regions of recycled gas at high redshift.The formation of the largest galaxies in the Universe is thought to be a two-stage process. For the last 10 Gyr, these giant galaxies have grown mostly by cannibalizing smaller galaxies (1,2). However, computer simulations predict that in an earlier phase, lasting a few Gyr, their stars condensed directly out of large reservoirs of accreted gas (3,4).We present observational evidence for an extended gas reservoir fueling star formation in the massive Spiderweb Galaxy, MRC 1138-262, which is located in a proto-cluster at a redshift of z = 2. 161 (5-9). The Spiderweb Galaxy is not a single galaxy, but an aggregation of protocluster galaxies. They are embedded in a giant halo of atomic (neutral and ionized) hydrogen gas, which radiates Lyα emission across a region of ~200 kpc (6). The central proto-cluster galaxy has a super-massive black hole at its core, which emits jets of relativistic particles visible in radio observations (5). Observations suggest that the proto-cluster galaxies will eventually merge and evolve into a single, giant elliptical galaxy in the center of the cluster (10). We therefore refer to the Spiderweb Galaxy as the entire region encompassed by the Lyα halo, and to the gas between the proto-cluster galaxies as the inter-galactic medium (IGM).Earlier observations of line emission by carbon-monoxide revealed the presence of large amounts of molecular gas in the Spiderweb Galaxy (11). Molecular gas is the raw fuel for the formation of stars, so observations of molecular gas give us insight into the processes driving the evolution of the distant Spiderweb Galaxy. We have obtained new, sensitive observations of 12 CO (J=1→0) with the Australia Telescope Compact Array (ATCA, 90 hour exposure time) and the Karl G. Jansky Very Large Array (VLA, 8 hour exposure time) (12). The ATCA observations were optimized for detecting low-surface-brightness emission from broadly distributed CO, with a 4.8ʺ″×3.5ʺ″ resolution. The VLA observations complement the ATCA data with a higher 0.7ʺ″×0.6ʺ″ resolution, sensitive to small-scale features but not to large-scale ones. Sampling these different spatial scales allows us to obtain a complete picture of the CO distribution, from the gas in the individual proto-cluster galaxies to that across the IGM. Figure 1 shows that the CO emission in the ATCA data covers a region of ~70 kpc around the central...

We present a CO(1-0) survey for cold molecular gas in a representative sample of 13 high-z radio galaxies (HzRGs) at 1.4 < z < 2.8, using the Australia Telescope Compact Array. We detect CO(1-0) emission associated with five sources: MRC 0114-211, MRC 0152-209, MRC 0156-252, MRC 1138-262 and MRC 2048-272. The CO(1-0) luminosities are in the range L CO ∼ (5 − 9) × 10 10 K km s −1 pc 2 . For MRC 0152-209 and MRC 1138-262 part of the CO(1-0) emission coincides with the radio galaxy, while part is spread on scales of tens of kpc and likely associated with galaxy mergers. The molecular gas mass derived for these two systems is M H2 ∼ 6 × 10 10 M (M H2 /L CO = 0.8). For the remaining three CO-detected sources, the CO(1-0) emission is located in the halo (∼50-kpc) environment. These three HzRGs are among the fainter far-IR emitters in our sample, suggesting that similar reservoirs of cold molecular halo gas may have been missed in earlier studies due to pre-selection of IR-bright sources. In all three cases the CO(1-0) is aligned along the radio axis and found beyond the brightest radio hot-spot, in a region devoid of 4.5µm emission in Spitzer imaging. The CO(1-0) profiles are broad, with velocity widths of ∼ 1000 -3600 km s −1 . We discuss several possible scenarios to explain these halo reservoirs of CO(1-0). Following these results, we complement our CO(1-0) study with detections of extended CO from the literature and find at marginal statistical significance (95% level) that CO in HzRGs is preferentially aligned towards the radio jet axis. For the eight sources in which we do not detect CO(1-0), we set realistic upper limits of L CO ∼ 3 − 4 × 10 10 K km s −1 pc 2 . Our survey reveals a CO(1-0) detection rate of 38%, allowing us to compare the CO(1-0) content of HzRGs with that of other types of high-z galaxies.

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We present high resolution, long-slit spectra of the jet-cloud interaction in the powerful southern radio galaxy PKS2250-41. We have resolved the emission lines into two main kinematic components: a broad component (FWHM≥900 km s −1 ) and a narrow component (FWHM≤150 km s −1 ). While the broad component is characterized by a low ionization level (with particularly weak HeIIλ4686 emission) and is spatially associated with the radio lobe, the narrow component is characterized by a higher ionization level and extends well beyond the radio lobe. Crucially, we measure a higher electron temperature for the broad component (T ∼30,000 K) than for the narrow component (T ∼15,000 K). The general line ratios and physical conditions of the two components are consistent with a model in which the broad component represents gas cooling behind the shock front driven by the radio jets, while the narrow component represents the AGN-or shock-photoionized precursor gas. However, uncertainties remain about the gas acceleration mechanism behind the shock front: unless the radio components are expanding unusually fast in this source, it is likely that entrainment of the warm clouds in the hot post-shock wind or radio plasma is required in addition to the initial acceleration across the shock front, in order to explain the large line widths of the broad component.The similarities between the kinematic properties of PKS2250-41 and some high redshift radio galaxies suggest that the ambient and the shocked gas have also been resolved in the more distant objects. Given the evidence that the emission line processes are affected by the interactions between the radio and the optical structures, care must be taken when interpreting the UV spectra of high redshift radio galaxies.

The circumgalactic medium (CGM) of the massive Spiderweb Galaxy, a conglomerate of merging proto-cluster galaxies at z=2.2, forms an enriched interface where feedback and recycling act on accreted gas. This is shown by observations of [C i], CO(1-0) and CO(4-3) performed with the Atacama Large Millimeter Array (ALMA) and Australia Telescope Compact Array (ATCA). [C i] and CO(4-3) are detected across ∼50 kpc, following the distribution of previously detected low-surface-brightness CO(1-0) across the CGM. This confirms our previous results on the presence of a cold molecular halo. The central radio galaxy MRC 1138-262 shows a very high global L CO(4-3)/L CO(1-0) ∼ 1, suggesting that mechanisms other than FUV-heating by star formation prevail at the heart of the Spiderweb Galaxy. Contrary, the CGM has L CO(4-3)/L CO(1-0) and L [CI]/L CO(1-0) similar to the ISM of five galaxies in the wider proto-cluster, and its carbon abundance, X[CI]/XH 2 , resembles that of the Milky Way and starforming galaxies. The molecular CGM is thus metal-rich and not diffuse, confirming a link between the cold gas and in-situ star formation. Thus, the Spiderweb Galaxy grows not directly through accretion of gas from the cosmic web, but from recycled gas in the GCM.

The high-redshift radio galaxy MRC 1138-262 ('Spiderweb Galaxy'; z = 2.16), is one of the most massive systems in the early Universe and surrounded by a dense 'web' of proto-cluster galaxies. Using the Australia Telescope Compact Array, we detected CO(1-0) emission from cold molecular gas -the raw ingredient for star formationacross the Spiderweb Galaxy. We infer a molecular gas mass of M H2 = 6 × 10 10 M ⊙ (for M H2 /L' CO = 0.8). While the bulk of the molecular gas coincides with the central radio galaxy, there are indications that a substantial fraction of this gas is associated with satellite galaxies or spread across the inter-galactic medium on scales of tens of kpc. In addition, we tentatively detect CO(1-0) in the star-forming proto-cluster galaxy HAE 229, 250 kpc to the west. Our observations are consistent with the fact that the Spiderweb Galaxy is building up its stellar mass through a massive burst of widespread star formation. At maximum star formation efficiency, the molecular gas will be able to sustain the current star formation rate (SFR ≈ 1400 M ⊙ yr −1 , as traced by Seymour et al.) for about 40 Myr. This is similar to the estimated typical lifetime of a major starburst event in infra-red luminous merger systems.

We present results on the spectroscopic study of the ionized gas in the high‐redshift radio galaxy USS0828+193 at z= 2.57. Thanks to the high signal‐to‐noise (S/N) ratio of the emission lines in the Keck spectrum, we have been able to perform a detailed kinematic study by means of the spectral decomposition of the emission line profiles. This study reveals the existence of two types of material in this object: (i) a low surface brightness component with apparent quiescent kinematics consistent with gravitational motions and (ii) a perturbed component with rather extreme kinematics. The quiescent halo extends across the entire object for ∼80 kpc. It is enriched with heavy elements and apparently ionized by the continuum from the active nucleus. The properties of the quiescent halo and its origin are discussed in this paper. We propose that it could be part of a structure that surrounds the entire object, although its nature is not clear (a rotating disc? low surface brightness satellites? a cooling flow nebula? material ejected in galactic winds? other?).