The ALPINE−ALMA [C ii] Survey: on the nature of an extremely obscured serendipitous galaxy. Issue 1 (4th June 2020)

• Record Type: Journal Article
• Authors: Romano, M; Cassata, P; Morselli, L; Lemaux, B C; Béthermin, M; Capak, P; Faisst, A; Le Fèvre, O; Schaerer, D; Silverman, J; Yan, L; Bardelli, S; Boquien, M; Cimatti, A; Dessauges-Zavadsky, M; Enia, A; Fudamoto, Y; Fujimoto, S; Ginolfi, M; Gruppioni, C; Hathi, N P; Ibar, E; Jones, G C; Koekemoer, A M; Loiacono, F; Mancini, C; Riechers, D A; Rodighiero, G; Rodríguez-Muñoz, L; Talia, M; Vallini, L; Vergani, D; Zamorani, G; Zucca, E;
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 496:Issue 1(2020)
• Page Start: 875
• Page End: 887
• Publication Date: 2020-06-04
• Subjects: galaxies: evolution -- galaxies: high-redshift; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/staa1546
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: 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 K s 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 $\mathrm{log}{(L_{[\mathrm{ C}\, \rm {\small {II}}]}/L_{\mathrm{ FIR}})} \sim -2.5$, 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 $\mathrm{log(SFR/M_{\odot }\, yr^{-1})}\sim 1.4$ 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.