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We present a CO(1-0) survey for cold molecular gas in a representative sampleof 13 high-z radio galaxies (HzRGs) at 1.4<z<2.8, using the Australia TelescopeCompact Array. We detect CO(1-0) emission associated with five sources: MRC0114-211, MRC 0152-209, MRC 0156-252, MRC 1138-262 and MRC 2048-272. TheCO(1-0) luminosities are in the range $L'_{\rm CO} \sim (5 - 9) \times 10^{10}$K km/s pc$^{2}$. For MRC 0152-209 and MRC 1138-262 part of the CO(1-0) emissioncoincides with the radio galaxy, while part is spread on scales of tens of kpcand likely associated with galaxy mergers. The molecular gas mass derived forthese two systems is M$_{\rm H2} \sim 6 \times 10^{10}\, {\rm M}_{\odot}$(M$_{\rm H2}$/$L'_{\rm CO}$=0.8). For the remaining three CO-detected sources,the CO(1-0) emission is located in the halo (~50-kpc) environment. These threeHzRGs are among the fainter far-IR emitters in our sample, suggesting thatsimilar reservoirs of cold molecular halo gas may have been missed in earlierstudies due to pre-selection of IR-bright sources. In all three cases theCO(1-0) is aligned along the radio axis and found beyond the brightest radiohot-spot, in a region devoid of 4.5$\mu$m emission in Spitzer imaging. TheCO(1-0) profiles are broad, with velocity widths of ~ 1000 - 3600 km/s. Wediscuss several possible scenarios to explain these halo reservoirs of CO(1-0).Following these results, we complement our CO(1-0) study with detections ofextended CO from the literature and find at marginal statistical significance(95% level) that CO in HzRGs is preferentially aligned towards the radio jetaxis. For the eight sources in which we do not detect CO(1-0), we set realisticupper limits of $L'_{\rm CO} \sim 3-4 \times 10^{10}$ K km/s pc$^{2}$. Oursurvey reveals a CO(1-0) detection rate of 38%, allowing us to compare theCO(1-0) content of HzRGs with that of other types of high-z galaxies.

CO(1-0) survey of high-z radio galaxies: alignment of molecular halo gas with distant radio sources