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 Ks filter. These SMGs are also faint in the radio waveband, where F6GHz = 4.5 μJy for ASXDF1100.053.1 and F1.4GHz = 28 μJy for ASXDF1100.231.1, suggestive of and 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⊙; their stellar masses are [0.9–2] × 1011 and [0.4–3] × 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, ΣIR, are ∼1 × 1012 and ≳1.5 × 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.