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We study the physical properties of a sample of 6 SMGs in the COSMOS field, spectroscopically confirmed to lie at z>4. We use new GMRT 325 MHz and 3 GHz JVLA data to probe the rest-frame 1.4 GHz emission at z=4, and to estimate the sizes of the star-forming (SF) regions of these sources, resp. Combining our size estimates with those available in the literature for AzTEC1 and AzTEC3 we infer a median radio-emitting size for our z>4 SMGs of (0.63"+/-0.12")x(0.35"+/-0.05") or 4.1x2.3 kpc^2 (major times minor axis; assuming z=4.5) or lower if we take the two marginally resolved SMGs as unresolved. This is consistent with the sizes of SF regions in lower-redshift SMGs, and local normal galaxies, yet higher than the sizes of SF regions of local ULIRGs. Our SMG sample consists of a fair mix of compact and more clumpy systems with multiple, perhaps merging, components. With an average formation time of ~280 Myr, derived through modeling of the UV-IR SEDs, the studied SMGs are young systems. The average stellar mass, dust temperature, and IR luminosity we derive are M*~1.4x10^11 M_sun, T_dust~43 K, and L_IR~1.3x10^13L_sun, resp. The average L_IR is up to an order of magnitude higher than for SMGs at lower redshifts. Our SMGs follow the correlation between dust temperature and IR luminosity as derived for Herschel-selected 0.1=1.95+/-0.26 for our sample, compared to q~2.6 for IR luminous galaxies at z4 SMGs put them at the high end of the L_IR-T_dust distribution of SMGs, and that our SMGs form a morphologically heterogeneous sample. Thus, further in-depth analyses of large, statistical samples of high-redshift SMGs are needed to fully understand their role in galaxy formation and evolution. ; This research was funded by the European Union's Seventh Framework program under grant agreement 337595 (ERC Starting Grant, "CoSMass"). A.K. acknowledges support by the Collaborative Research Council 956, subproject A1, funded by the Deutsche Forschungsgemeinschaft (DFG). The Dark Cosmology Centre is funded by the Danish National Research Foundation.

We study the physical properties of a sample of 6 SMGs in the COSMOS field, spectroscopically confirmed to lie at z>4. We use new GMRT 325 MHz and 3 GHz JVLA data to probe the rest-frame 1.4 GHz emission at z=4, and to estimate the sizes of the star-forming (SF) regions of these sources, resp. Combining our size estimates with those available in the literature for AzTEC1 and AzTEC3 we infer a median radio-emitting size for our z>4 SMGs of (0.63"+/-0.12")x(0.35"+/-0.05") or 4.1x2.3 kpc^2 (major times minor axis; assuming z=4.5) or lower if we take the two marginally resolved SMGs as unresolved. This is consistent with the sizes of SF regions in lower-redshift SMGs, and local normal galaxies, yet higher than the sizes of SF regions of local ULIRGs. Our SMG sample consists of a fair mix of compact and more clumpy systems with multiple, perhaps merging, components. With an average formation time of ~280 Myr, derived through modeling of the UV-IR SEDs, the studied SMGs are young systems. The average stellar mass, dust temperature, and IR luminosity we derive are M*~1.4x10^11 M_sun, T_dust~43 K, and L_IR~1.3x10^13L_sun, resp. The average L_IR is up to an order of magnitude higher than for SMGs at lower redshifts. Our SMGs follow the correlation between dust temperature and IR luminosity as derived for Herschel-selected 0.1=1.95+/-0.26 for our sample, compared to q~2.6 for IR luminous galaxies at z4 SMGs put them at the high end of the L_IR-T_dust distribution of SMGs, and that our SMGs form a morphologically heterogeneous sample. Thus, further in-depth analyses of large, statistical samples of high-redshift SMGs are needed to fully understand their role in galaxy formation and evolution. ; This research was funded by the European Union's Seventh Framework program under grant agreement 337595 (ERC Starting Grant, "CoSMass"). A.K. acknowledges support by the Collaborative Research Council 956, subproject A1, funded by the Deutsche Forschungsgemeinschaft (DFG). The Dark Cosmology Centre is funded by the Danish National Research Foundation.

Dust-enshrouded, starbursting, submillimeter galaxies (SMGs) at z ≥ 3 have been proposed as progenitors of z ≥ 2 compact quiescent galaxies (cQGs). To test this connection, we present a detailed spatially resolved study of the stars, dust, and stellar mass in a sample of six submillimeter-bright starburst galaxies at z ∼ 4.5. The stellar UV emission probed by HST is extended and irregular and shows evidence of multiple components. Informed by HST, we deblend Spitzer/IRAC data at rest-frame optical, finding that the systems are undergoing minor mergers with a typical stellar mass ratio of 1:6.5. The FIR dust continuum emission traced by ALMA locates the bulk of star formation in extremely compact regions (median r = 0.70 ± 0.29 kpc), and it is in all cases associated with the most massive component of the mergers (median ). We compare spatially resolved UV slope (β) maps with the FIR dust continuum to study the infrared excess (IRX = L /L )-β relation. The SMGs display systematically higher IRX values than expected from the nominal trend, demonstrating that the FIR and UV emissions are spatially disconnected. Finally, we show that the SMGs fall on the mass-size plane at smaller stellar masses and sizes than the cQGs at z = 2. Taking into account the expected evolution in stellar mass and size between z = 4.5 and z = 2 due to the ongoing starburst and mergers with minor companions, this is in agreement with a direct evolutionary connection between the two populations. © 2018. The American Astronomical Society. All rights reserved. ; C.G.G. and S.T. acknowledge support from the European Research Council (ERC) Consolidator Grant funding scheme (project ConTExt, grant number 648179). A.K., E.J.A., and F.B. acknowledge support by the Collaborative Research Centre 956, subproject A1, funded by the Deutsche Forschungsgemeinschaft (DFG). Support for B.M. was provided by the DFG priority program 1573, "The physics of the interstellar medium." D.R. acknowledges support from the National Science Foundation under grant number AST-1614213. V.S. acknowledges support from the European Union's Seventh Framework program under grant agreement 337595 (ERC Starting Grant, "CoSMass"). M.A. acknowledges partial support from FONDECYT through grant 1140099. ERD also acknowledge support by the Collaborative Research Centre 956, subproject C4, funded by the DFG. M.J.M. acknowledges the support of the National Science Centre, Poland, through POLONEZ grant 2015/19/P/ST9/04010; this project has received funding from the European Union's Horizon 2020 research and innovation program under Marie Sklodowska-Curie grant agreement No. 665778. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program #13294. Support for program #13294 was provided by NASA through a grant from the Space Telescope Science Institute.