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arXiv · 2002.00961

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

Michael Romano·P. Cassata·L. Morselli·B. C. Lemaux·M. Bethermin·P. Capak·A. Faisst·O. Le Fevre·D. Schaerer·J. Silverman·L. Yan·S. Bardelli·M. Boquien·A. Cimatti·M. Dessauges-Zavadsky·A. Enia·Y. Fudamoto·S. Fujimoto·M. Ginolfi·C. Gruppioni·N. P. Hathi·E. Ibar·G. C. Jones·A. M. Koekemoer·F. Loiacono·C. Mancini·D. A. Riechers·G. Rodighiero·L. Rodriguez-Munoz·M. Talia·L. Vallini·D. Vergani·G. Zamorani·E. Zucca
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Abstract

We report the serendipitous discovery of a bright galaxy (Gal-A) observed as part of the ALMA Large Program to INvestigate [CII] at Early times (ALPINE). While this galaxy is detected both in line and continuum emission in ALMA Band 7, it is completely dark in UV/optical filters and only presents a marginal detection in the UltraVISTA Ks band. We discuss the nature of the observed ALMA line, i.e. whether the emission comes from [CII] at z~4.6, or from high-J CO transitions at z~2.2. In the first case we find a [CII]-to-FIR luminosity ratio of log(L_[CII]/L_FIR)=-2.5, consistent with the average value for local star-forming galaxies (SFGs); in the second case, instead, the source would lie outside of the empirical relations between L_CO and L_FIR found in the literature. At both redshifts, we derive the star-formation rate (SFR) from the ALMA continuum, and the stellar mass (M*) by using stellar population synthesis models as input for LePHARE spectral energy distribution (SED) fitting. Exploiting our results, we believe that Gal-A is a Main-Sequence (MS), dusty SFG at z=4.6 (i.e. [CII] emitter) with log(SFR/[M/yr])~1.4 and log(M*/M)~9.7. 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 star-formation rate density (SFRD) of the Universe at the end of the Reionisation epoch.

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Michael Romano, P. Cassata, L. Morselli, B. C. Lemaux, M. Bethermin, P. Capak, A. Faisst, O. Le Fevre, D. Schaerer, J. Silverman, L. Yan, S. Bardelli, M. Boquien, A. Cimatti, M. Dessauges-Zavadsky, A. Enia, Y. Fudamoto, S. Fujimoto, M. Ginolfi, C. Gruppioni, N. P. Hathi, E. Ibar, G. C. Jones, A. M. Koekemoer, F. Loiacono, C. Mancini, D. A. Riechers, G. Rodighiero, L. Rodriguez-Munoz, M. Talia, L. Vallini, D. Vergani, G. Zamorani, E. Zucca. 2020-02-03. The ALPINE-ALMA [CII] Survey: On the nature of an extremely obscured serendipitous galaxy. https://doi.org/10.1093/mnras/staa1546

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