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CO, H2O, H2O+ line and dust emission in a z = 3.63 strongly lensed starburst merger at sub-kiloparsec scales.

Yang, C. and Gavazzi, R. and Beelen, A. and Cox, P. and Omont, A. and Lehnert, M. D. and Gao, Y. and Ivison, R. J. and Swinbank, A. M. and Barcos-Muñoz, L. and Neri, R. and Cooray, A. and Dye, S. and Eales, S. and Fu, H. and González-Alfonso, E. and Ibar, E. and Michałowski, M. J. and Nayyeri, H. and Negrello, M. and Nightingale, J. and Pérez-Fournon, I. and Riechers, D. A. and Smail, I. and van der Werf, P. (2019) 'CO, H2O, H2O+ line and dust emission in a z = 3.63 strongly lensed starburst merger at sub-kiloparsec scales.', Astronomy & astrophysics., 624 . A138.


Using the Atacama Large Millimeter/submillimeter Array (ALMA), we report high angular-resolution observations of the redshift z  = 3.63 galaxy H-ATLAS J083051.0+013224 (G09v1.97), one of the most luminous strongly lensed galaxies discovered by the Herschel-Astrophysical Terahertz Large Area Survey (H-ATLAS). We present 0.″2−0.″4 resolution images of the rest-frame 188 and 419 μm dust continuum and the CO(6–5), H2O(211−202), and Jup = 2 H2O+ line emission. We also report the detection of H2O(211−202) in this source. The dust continuum and molecular gas emission are resolved into a nearly complete ∼1.″5 diameter Einstein ring plus a weaker image in the center, which is caused by a special dual deflector lensing configuration. The observed line profiles of the CO(6–5), H2O(211−202), and Jup = 2 H2O+ lines are strikingly similar. In the source plane, we reconstruct the dust continuum images and the spectral cubes of the CO, H2O, and H2O+ line emission at sub-kiloparsec scales. The reconstructed dust emission in the source plane is dominated by a compact disk with an effective radius of 0.7 ± 0.1 kpc plus an overlapping extended disk with a radius twice as large. While the average magnification for the dust continuum is μ ∼ 10−11, the magnification of the line emission varies from 5 to 22 across different velocity components. The line emission of CO(6–5), H2O(211−202), and H2O+ have similar spatial and kinematic distributions. The molecular gas and dust content reveal that G09v1.97 is a gas-rich major merger in its pre-coalescence phase, with a total molecular gas mass of ∼1011 M⊙. Both of the merging companions are intrinsically ultra-luminous infrared galaxies (ULIRGs) with infrared luminosities LIR reaching ≳4 × 1012 L⊙, and the total LIR of G09v1.97 is (1.4 ± 0.7)×1013 L⊙. The approaching southern galaxy (dominating from V = −400 to −150 km s−1 relative to the systemic velocity) shows no obvious kinematic structure with a semi-major half-light radius of as = 0.4 kpc, while the receding galaxy (0 to 350 km s−1) resembles an as = 1.2 kpc rotating disk. The two galaxies are separated by a projected distance of 1.3 kpc, bridged by weak line emission (−150 to 0 km s−1) that is co-spatially located with the cold dust emission peak, suggesting a large amount of cold interstellar medium (ISM) in the interacting region. As one of the most luminous star-forming dusty high-redshift galaxies, G09v1.97 is an exceptional source for understanding the ISM in gas-rich starbursting major merging systems at high redshift.

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Publisher statement:Yang, C., Gavazzi, R., Beelen, A., Cox, P., Omont, A., Lehnert, M. D., Gao, Y., Ivison, R. J., Swinbank, A. M., Barcos-Muñoz, L., Neri, R., Cooray, A., Dye, S., Eales, S., Fu, H., González-Alfonso, E., Ibar, E., Michałowski, M. J., Nayyeri, H., Negrello, M., Nightingale, J., Pérez-Fournon, I., Riechers, D. A., Smail, I. & van der Werf, P. (2019). CO, H2O, H2O+ line and dust emission in a z = 3.63 strongly lensed starburst merger at sub-kiloparsec scales. Astronomy & Astrophysics 624: A138., reproduced with permission,© ESO.
Date accepted:28 February 2019
Date deposited:10 May 2019
Date of first online publication:26 April 2019
Date first made open access:10 May 2019

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