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Register a new userCO(1-0) in z>2 Quasar Host Galaxies: No Evidence for Extended Molecular Gas Reservoirs
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Dominik A. Riechers
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We report the detection of CO(1-0) emission in the strongly lensed high-redshift quasars IRAS F10214+4724 (z=2.286), the Cloverleaf (z=2.558), RX J0911+0551 (z=2.796), SMM J04135+10277 (z=2.846), and MG 0751+2716 (z=3.200), using the Expanded Very Large Array and the Green Bank Telescope. We report lensing-corrected CO(1-0) line luminosities of L(CO) = 0.34-18.4 x 10^10 K km/s pc^2 and total molecular gas masses of M(H2) = 0.27-14.7 x 10^10 Msun for the sources in our sample. Based on CO line ratios relative to previously reported observations in J>=3 rotational transitions and line excitation modeling, we find that the CO(1-0) line strengths in our targets are consistent with single, highly-excited gas components with constant brightness temperature up to mid-J levels. We thus do not find any evidence for luminous extended, low excitation, low surface brightness molecular gas components. These properties are comparable to those found in z>4 quasars with existing CO(1-0) observations. These findings stand in contrast to recent CO(1-0) observations of z~2-4 submillimeter galaxies (SMGs), which have lower CO excitation and show evidence for multiple excitation components, including some low-excitation gas. These findings are consistent with the picture that gas-rich quasars and SMGs represent different stages in the early evolution of massive galaxies.
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We present CO(1-0) observations of the high-redshift quasi-stellar objects (QSOs) BR 1202-0725 (z=4.69), PSS J2322+1944 (z=4.12), and APM 08279+5255 (z=3.91) using the NRAO Green Bank Telescope (GBT) and the MPIfR Effelsberg 100m telescope. We detect, for the first time, the CO ground-level transition in BR 1202-0725. For PSS J2322+1944 and APM 08279+5255, our observations result in line fluxes that are consistent with previous NRAO Very Large Array (VLA) observations, but they reveal the full line profiles. We report a typical lensing-corrected velocity-integrated intrinsic CO(1-0) line luminosity of L(CO) = 5 x 10^10 K km/s pc^2 and a typical total H_2 mass of M(H2) = 4 x 10^10 M_sun for the sources in our sample. The CO/FIR luminosity ratios of these high-z sources follow the same trend as seen for low-z galaxies, leading to a combined solution of log(L_FIR) = (1.39 +/- 0.05) x log(L(CO))-1.76. It has previously been suggested that the molecular gas reservoirs in some quasar host galaxies may exhibit luminous, extended CO(1-0) components that are not observed in the higher-J CO transitions. Utilizing the line profiles and the total intensities of our observations and large velocity gradient (LVG) models based on previous results for higher-J CO transitions, we derive that emission from all CO transitions is described well by a single gas component where all molecular gas is concentrated in a compact nuclear region. Thus, our observations and models show no indication of a luminous extended, low surface brightness molecular gas component in any of the high-redshift QSOs in our sample. If such extended components exist, their contribution to the overall luminosity is limited to at most 30%.
We report the detection of spatially resolved CO(1-0) emission in the z~3.4 submillimeter galaxies (SMGs) SMM J09431+4700 and SMM J13120+4242, using the Expanded Very Large Array (EVLA). SMM J09431+4700 is resolved into the two previously reported millimeter sources H6 and H7, separated by ~30kpc in projection. We derive CO(1-0) line luminosities of L(CO 1-0) = (2.49+/-0.86) and (5.82+/-1.22) x 10^10 K km/s pc^2 for H6 and H7, and L(CO 1-0) = (23.4+/-4.1) x 10^10 K km/s pc^2 for SMM J13120+4242. These are ~1.5-4.5x higher than what is expected from simple excitation modeling of higher-J CO lines, suggesting the presence of copious amounts of low-excitation gas. This is supported by the finding that the CO(1-0) line in SMM J13120+4242, the system with lowest CO excitation, appears to have a broader profile and more extended spatial structure than seen in higher-J CO lines (which is less prominently seen in SMM J09431+4700). Based on L(CO 1-0) and excitation modeling, we find M_gas = 2.0-4.3 and 4.7-12.7 x 10^10 Msun for H6 and H7, and M_gas = 18.7-69.4 x 10^10 Msun for SMM J13120+4242. The observed CO(1-0) properties are consistent with the picture that SMM J09431+4700 represents an early-stage, gas-rich major merger, and that SMM J13120+4242 represents such a system in an advanced stage. This study thus highlights the importance of spatially and dynamically resolved CO(1-0) observations of SMGs to further understand the gas physics that drive star formation in these distant galaxies, which becomes possible only now that the EVLA rises to its full capabilities.
We test the use of long-wavelength dust continuum emission as a molecular gas tracer at high redshift, via a unique sample of 12, z~2 galaxies with observations of both the dust continuum and CO(1-0) line emission (obtained with the Atacama Large Millimeter Array and Karl G. Jansky Very Large Array, respectively). Our work is motivated by recent, high redshift studies that measure molecular gas masses (ensuremath{rm{M}_{rm{mol}}}) via a calibration of the rest-frame $850mu$m luminosity ($L_mathrm{850mu m,rest}$) against the CO(1-0)-derived ensuremath{rm{M}_{rm{mol}}} of star-forming galaxies. We hereby test whether this method is valid for the types of high-redshift, star-forming galaxies to which it has been applied. We recover a clear correlation between the rest-frame $850mu$m luminosity, inferred from the single-band, long-wavelength flux, and the CO(1-0) line luminosity, consistent with the samples used to perform the $850mu$m calibration. The molecular gas masses, derived from $L_mathrm{850mu m,rest}$, agree to within a factor of two with those derived from CO(1-0). We show that this factor of two uncertainty can arise from the values of the dust emissivity index and temperature that need to be assumed in order to extrapolate from the observed frequency to the rest-frame at 850$mathrm{mu m}$. The extrapolation to 850$mathrm{mu m}$ therefore has a smaller effect on the accuracy of Mmol derived via single-band dust-continuum observations than the assumed CO(1-0)-to-ensuremath{rm{M}_{rm{mol}}} conversion factor. We therefore conclude that single-band observations of long-wavelength dust emission can be used to reliably constrain the molecular gas masses of massive, star-forming galaxies at $zgtrsim2$.
We report the detection of molecular CO(1-0) gas in the high-z radio galaxy MRC 0152-209 (z = 1.92) with the Australia Telescope Compact Array Broadband Backend (ATCA/CABB). This is the third known detection of CO(1-0) in a high-z radio galaxy to date. CO(1-0) is the most robust tracer of the overall molecular gas content (including the wide-spread, low-density and subthermally excited component), hence observations of CO(1-0) are crucial for studying galaxy evolution in the Early Universe. We derive L(CO) = (6.6 +- 2.0) x 10^10 K km/s pc^2 for MRC 0152-209, which is comparable to that derived from CO(1-0) observations of several high-z submillimetre and starforming BzK galaxies. The CO(1-0) traces a total molecular hydrogen mass of M(H2) = 5 x 10^10 (alpha_x/0.8) Msun. MRC 0152-209 is an infra-red bright radio galaxy, in which a large reservoir of cold molecular gas has not (yet) been depleted by star formation or radio source feedback. Its compact radio source is reliably detected at 40 GHz and has a steep spectral index of alpha = -1.3 between 1.4 and 40 GHz (4-115 GHz in the galaxys rest-frame). MRC 0152-209 is part of an ongoing systematic ATCA/CABB survey of CO(1-0) in high-z radio galaxies between 1.7 < z < 3.
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 M(H2) = 6x10^10 M(sun) (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(sun)/yr, 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.
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