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

Abstract

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 μ m, and are observed by Herschel to be faint at 100–500 μ m. 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 μ Jy at IRAC 4.5 μ m and <0.2 μ Jy in the K s filter. These SMGs are also faint in the radio waveband, where F 6GHz  = 4.5 μ Jy for ASXDF1100.053.1 and F 1.4GHz  = 28 μ Jy 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 μ m filter, probably due to H α 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] × 10 12 and [4.2–4.5] × 10 12 L ⊙ ; their stellar masses are [0.9–2] × 10 11 and [0.4–3] × 10 10 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 × 10 12 and ≳1.5 × 10 13 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.