Abstract
We have modelled Atacama Large Millimeter/sub-millimeter Array (ALMA) long baseline imaging of the strong gravitational lens system H-ATLAS J090311.6+003906 (SDP.81). We have reconstructed the distribution of band 6 and 7 continuum emission in the z=3.042 source and we have determined its kinematic properties by reconstructing CO(5-4) and CO(8-7) line emission in bands 4 and 6. The continuum imaging reveals a highly non-uniform distribution of dust with clumps on scales of 200 pc. In contrast, the CO line emission shows a relatively smooth, disk-like velocity field which is well fit by a rotating disk model with an inclination angle of 40+/-5 degrees and an asymptotic rotation velocity of 320 km/s. The inferred dynamical mass within 1.5kpc is (3.5+/-0.5)x10^{10} M_sol which is comparable to the total molecular gas masses of (2.7+/-0.5)x10^{10} M_sol and (3.5+/-0.6)x10^{10} M_sol from the dust continuum emission and CO emission respectively. Our new reconstruction of the lensed HST near-infrared emission shows two objects which appear to be interacting, with the rotating disk of gas and dust revealed by ALMA distinctly offset from the near-infrared emission. The clumpy nature of the dust and a low value of the Toomre parameter of Q=0.3 suggest that the disk is in a state of collapse. We estimate a star formation rate in the disk of 470+/-80 M_sol/yr with an efficiency 65 times greater than typical low-redshift galaxies. Our findings add to the growing body of evidence that the most infra-red luminous, dust obscured galaxies in the high redshift Universe represent a population of merger induced starbursts.
Highlights
Our understanding of high-redshift sub-millimetre bright galaxies (SMGs) has grown immensely since their discovery nearly two decades ago (Smail, Ivison & Blain 1997; Barger et al 1998;C 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical SocietyHughes et al 1998)
Kpc−2 who performed uv modelling of the same Atacama Large Millimetre/sub-millimetre Array (ALMA) data we have analysed in the present work
D14 found good alignment between the rest-frame optical emission and the submm source reconstructed by Bussmann et al (2013), this latter study used imaging acquired with the Submillimetre Array (SMA) with a beam width approximately two orders of magnitude larger than the ALMA image data analysed in the present work
Summary
Our understanding of high-redshift sub-millimetre (submm) bright galaxies (SMGs) has grown immensely since their discovery nearly two decades ago (Smail, Ivison & Blain 1997; Barger et al 1998;Hughes et al 1998). Our understanding of high-redshift sub-millimetre (submm) bright galaxies (SMGs) has grown immensely since their discovery nearly two decades ago The fact that approximately half of the total energy output from stars within the observable history of the Universe has been absorbed by dust and re-emitted at submm wavelengths (Puget et al 1996; Fixsen et al 1998) and that SMGs represent the most active sites of dusty star formation at high redshifts indicates that their role in early galaxy formation is an important one. Morphological and kinematical measurements of SMGs have led many studies to conclude that they are a more energetic version of more local ultra-luminous infrared galaxies (ULIRGs; e.g. Engel et al 2010; Swinbank et al 2010; Alaghband-Zadeh et al 2012; Rowlands et al 2014). A reliance has traditionally been made on correlations with other wavelengths which often only result in indirect diagnostics of the internal energetics of the physical processes at work in these galaxies
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