Cooke, E. A. and Smail, Ian and Swinbank, A. M. and Stach, S. M. and An, Fang Xia and Gullberg, B. and Almaini, O. and Simpson, C. J. and Wardlow, J. L. and Blain, A. W. and Chapman, S. C. and Chen, Chian-Chou and Conselice, C. J. and Coppin, K. E. K. and Farrah, D. and Maltby, D. T. and Michałowski, M. J. and Scott, D. and Simpson, J. M. and Thomson, A. P. and van der Werf, P. (2018) An ALMA Survey of the SCUBA-2 Cosmology Legacy Survey UKIDSS/UDS Field: Identifying Candidate z ˜ 4.5 [C II] Emitters. The Astrophysical Journal, 861 (2): 100. ISSN 0004-637X
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Abstract
We report the results of a search for serendipitous [C II] 157.74 μm emitters at z ≃ 4.4-4.7 using the Atacama Large Millimeter/submillimeter Array (ALMA). The search exploits the AS2UDS continuum survey, which covers ˜50 arcmin2 of the sky toward 695 luminous (S 870 ≳ 1 mJy) submillimeter galaxies (SMGs), selected from the SCUBA-2 Cosmology Legacy Survey 0.96 deg2 Ultra Deep Survey (UDS) field. We detect 10 candidate line emitters, with an expected false detection rate of 10%. All of these line emitters correspond to 870 μm continuum-detected sources in AS2UDS. The emission lines in two emitters appear to be high-J CO, but the remainder have multi-wavelength properties consistent with [C II] from z ≃ 4.5 galaxies. Using our sample, we place a lower limit of > 5× {10}-6 {Mpc}}-3 on the space density of luminous (L IR ≃ 1013 {L}⊙ ) SMGs at z = 4.40-4.66, suggesting ≥slant 7% of SMGs with {S}870μ {{m}}≳ 1 mJy lie at 4 <z <5. From stacking the high-resolution (˜0.″15 full-width half maximum) ALMA 870 μm imaging, we show that the [C II] line emission is more extended than the continuum dust emission, with an average effective radius for the [C II] of {r}{{e}}={1.7}-0.2+0.1 kpc, compared to r e = 1.0 ± 0.1 kpc for the continuum (rest-frame 160 μm). By fitting the far-infrared photometry for these galaxies from 100 to 870 μm, we show that SMGs at z ˜ 4.5 have a median dust temperature of T d = 55 ± 4 K. This is systematically warmer than 870 μm selected SMGs at z ≃ 2, which typically have temperatures around 35 K. These z ≃ 4.5 SMGs display a steeper trend in the luminosity-temperature plane than z ≤ 2 SMGs. We discuss the implications of this result in terms of the selection biases of high-redshift starbursts in far-infrared/submillimeter surveys.