2017ApJ...835..286I

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. These SMGs were originally selected using AzTEC at 1100 µm, and are observed by Herschel to be faint at 100-500 µm. 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 µJy at IRAC 4.5 µm and <0.2 µJy in the K_s filter. These SMGs are also faint in the radio waveband, where F_6GHz = 4.5 µJy for ASXDF1100.053.1 and F_1.4GHz = 28 µJy for ASXDF1100.231.1, suggestive of z=6.5_–1.1^+1.4 and z=4.1_–0.7^+0.6 for ASXDF1100.053.1 and 231.1, respectively. ASXDF1100.231.1 has a flux excess in the 3.6 µm filter, probably due to Hα 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] x 10¹² and [4.2-4.5] x 10¹² L_☉; their stellar masses are [0.9-2] x 10¹¹ and [0.4-3] x 10¹⁰ M_☉; their circularized half-light radii in the ALMA maps are ∼1 and <=0.2 kpc (∼2-3 kpc for 90% of the total flux). Last, their surface infrared luminosity densities, Σ_IR, are ∼1 x 10¹² and >=1.5 x 10¹³ L_☉ 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.