* Astronomy

Title: Extremely Red Submillimeter Galaxies: New z>~4-6 Candidates Discovered using ALMA and Jansky VLA
Author: Soh Ikarashi (1), R. J. Ivison (2 and 3), Karina I. Caputi (1), Koichiro Nakanishi (4, 5 and 6), Claudia D. P. Lagos (7), M. L. N. Ashby (8), Itziar Aretxaga (9), James S. Dunlop (2), Bunyo Hatsukade (4), David H. Hughes (9), Daisuke Iono (4 and 5), Takuma Izumi (10), Ryohei Kawabe (4 and 5), Kotaro Kohno (10 and 11), Kentaro Motohara (10), Kouji Ohta (12), Yoichi Tamura (10), Hideki Umehata (10 and 13), Grant W. Wilson (14), Kiyoto Yabe (15), Min S. Yun (14) ((1) Kapteyn Astronomical Institute, University of Groningen, (2) Institute for Astronomy, University of Edinburgh, (3) European Southern Observatory, (4) National Astronomical Observatory of Japan, (5) The Graduate University for Advanced Studies (SOKENDAI), (6) Joint ALMA Observatory, (7) International Centre for Radio Astronomy Research, University of Western Australia, (8) Harvard-Smithsonian Center for Astrophysics, (9) Instituto Nacional de Astrofísica, Optica y Electrónica (INAOE), (10) Institute of Astronomy, University of Tokyo, (11) Research Center for the Early Universe, School of Science, University of Tokyo, (12) Kyoto University, (13) The Open University of Japan, (14) University of Massachusetts, (15) Kavli Institute for the Physics and Mathematics of the Universe (WPI), The University of Tokyo)

We present the detailed characterization of two extremely red submillimeter galaxies (SMGs), ASXDF1100.053.1 and 231.1, with the Atacama Large Millimeter/submillimeter Array (ALMA) and the Jansky Very Large Array (VLA). These SMGs were selected originally using AzTEC at 1100 micron, and are observed by Herschel to be faint at 100--500 micron. Their (sub)millimeter colors are as red as -- or redder -- than known z>~5 SMGs; indeed, ASXDF1100.053.1 is redder than HFLS 3, which lies at z=6.3. They are also faint and red in the near-/mid-infrared: ~1 microJy at IRAC 4.5 micron and <0.2 microJy in the Ks filter. These SMGs are also faint in the radio waveband, where F_6GHz=4.5 microJy for ASXDF1100.053.1 and F_1.4GHz=28 microJy for ASXDF1100.231.1, suggestive of z=6.5^{+1.4}_{-1.1} and z=4.1^{+0.6}_{-0.7} for ASXDF1100.053.1 and 231.1, respectively. ASXDF1100.231.1 has a flux excess in the 3.6-micron filter, probably due to H emission at z=4--5. Derived properties of ASXDF1100.053.1 for z=5.5--7.5 and 231.1 for z=3.5--5.5 are as follows: their infrared luminosities are [6.5-7.4]x10^{12} and [4.2-4.5]x10^{12} L_sun; their stellar masses are [0.9-2]x10^{11} and [0.4-3]x10^{10} M_sun; their circularized half-light radii in the ALMA maps are ~1 and <~0.2 kpc (~2--3 kpc for 90% of the total flux). Lastly, their surface infrared luminosity densities, Sigma_IR, are ~1x10^{12} and >~1.5x10^{13} L_sun kpc^{-2}, similar to values seen for local (U)LIRGs. These data suggest that ASXDF1100.053.1 and 231.1 are compact SMGs at z>~4 and can plausibly evolve into z>~3 compact quiescent galaxies.

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