VLA imaging of 12CO J = 1-0 and free-free emission in lensed submillimetre galaxies

We present a study using the Karl G. Jansky Very Large Array (VLA) of 12CO J = 1-0 emission in three strongly lensed submillimetre-selected galaxies (SMM J16359, SMM J14009 and SMM J02399) at z = 2.5-2.9. These galaxies span LIR = 1011-1013 L⊙, offering an opportunity to compare the interstellar medium of luminous infrared galaxies and ultraluminous infrared galaxies at high redshift. We estimate molecular gas masses in the range of 2-40 × 109 M⊙ using a method that assumes canonical underlying brightness temperature (Tb) ratios for star-forming and non-star-forming gas phases and a maximal star formation efficiency. A more simplistic method - using XCO = 0.8 and the measured Tb ratios - yields gas masses twice as high. In SMM J14009 we find L CO 3-2'/L CO 1-0'=0.95±0.12, indicative of warm, star-forming gas, possibly influenced by the central active galactic nucleus (AGN). We set a gas mass limit of 3σ < 6 × 108 M⊙ for the Lyman break galaxy, A2218 #384, located in the same field as SMM J16359 at z = 2.515. Finally, we use the rest-frame ˜115 GHz free-free flux densities for SMM J14009 and SMM J02399 - measurements tied directly to the photoionization rate of massive stars, and made possible by VLA's bandwidth - to estimate star formation rates (SFRs) of 400-600 M⊙ yr-1 and to estimate the fraction of LIR due to AGN

CO(1-0) detection of molecular gas in the massive Spiderweb Galaxy (z=2)

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 formation – across the Spiderweb Galaxy. We infer a molecular gas mass of MH2 = 6 × 1010 M⊙ (for MH2/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 intergalactic 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 infrared luminous merger systems

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

We present a CO(1–0) survey for cold molecular gas in a representative sample of 13 highz 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) × 1010 K km s−1 pc2. 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 MH2 ∼ 6 × 1010 M� (MH2/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 hotspot, in a region devoid of 4.5 µm emission in Spitzerimaging. 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 per cent 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 × 1010 K km s−1 pc2. Our survey reveals a CO(1–0) detection rate of 38 per cent, allowing us to compare the CO(1–0) content of HzRGs with that of other types of high-z galaxies