The ALPINE-ALMA [C II] Survey: On the nature of an extremely obscured serendipitous galaxy

M. Romano*, P. Cassata, L. Morselli, B. C. Lemaux, M. M. Béthermin, P. Capak, A. Faisst, O. Le Fèvre, D. Schaerer, J. Silverman, L. Yan, S. Bardelli, M. Boquien, A. Cimatti, M. Dessauges-Zavadsky, A. Enia, Y. Fudamoto, S. Fujimoto, M. Ginolfi, C. GruppioniN. P. Hathi, E. Ibar, G. C. Jones, A. M. Koekemoer, F. Loiacono, C. Mancini, D. A. Riechers, G. Rodighiero, L. Rodríguez-Muñoz, M. Talia, L. Vallini, D. Vergani, G. Zamorani, E. Zucca

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

15 Citations (Scopus)


We report the serendipitous discovery of a dust-obscured galaxy observed as part of the Atacama Large Millimeter Array (ALMA) Large Program to INvestigate [C ii] at Early times (ALPINE). While this galaxy is detected both in line and continuum emissions in ALMA Band 7, it is completely dark in the observed optical/near-infrared bands and only shows a significant detection in the UltraVISTA Ks band. We discuss the nature of the observed ALMA line, that is [C ii] at z ∼4.6 or high-J CO transitions at z ∼2.2. In the first case, we find a [C ii]/FIR luminosity ratio of log(L-[C\rm small II]/L FIR) ∼-2.5, consistent with the average value for local star-forming galaxies (SFGs). In the second case instead, the source would lie at larger CO luminosities than those expected for local SFGs and high-z submillimetre galaxies. At both redshifts, we derive the star formation rate (SFR) from the ALMA continuum and the physical parameters of the galaxy, such as the stellar mass (M), by fitting its spectral energy distribution. Exploiting the results of this work, we believe that our source is a 'main-sequence', dusty SFG at z = 4.6 (i.e. [C ii] emitter) with log(SFR/M⊙ yr-1)∼ 1.4 and log(M/M·) ∼9.9. As a support to this scenario our galaxy, if at this redshift, lies in a massive protocluster recently discovered at z ∼4.57, at only ∼1 proper Mpc from its centre. This work underlines the crucial role of the ALPINE survey in making a census of this class of objects, in order to unveil their contribution to the global SFR density at the end of the Reionization epoch.

Original languageEnglish
Pages (from-to)875-887
Number of pages13
JournalMonthly Notices of the Royal Astronomical Society
Issue number1
Publication statusPublished - 2020 Jun 11
Externally publishedYes


  • galaxies: evolution
  • galaxies: high-redshift

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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