Extremely Red Submillimeter Galaxies: New z ≳ 4-6 Candidates Discovered Using ALMA and Jansky VLA

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^+1.4 _-1.1 and z= 4.1^+0.6 _-0.7and 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] ×10¹² and [4.2-4.5] ×10¹² L _o; their stellar masses are [0.9-2] ×10¹¹ and [0.4-3] ×10¹⁰ M _o; 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 ×10¹² and ≳1.5 ×10¹³ L _o 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.