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# ALMA Lensing Cluster Survey: Bright [C ii] 158 μm Lines from a Multiply Imaged Sub-L⋆ Galaxy at z = 6.0719

Fujimoto, Seiji and Oguri, Masamune and Brammer, Gabriel and Yoshimura, Yuki and Laporte, Nicolas and González-López, Jorge and Caminha, Gabriel B. and Kohno, Kotaro and Zitrin, Adi and Richard, Johan and Ouchi, Masami and Bauer, Franz E. and Smail, Ian and Hatsukade, Bunyo and Ono, Yoshiaki and Kokorev, Vasily and Umehata, Hideki and Schaerer, Daniel and Knudsen, Kirsten and Sun, Fengwu and Magdis, Georgios and Valentino, Francesco and Ao, Yiping and Toft, Sune and Dessauges-Zavadsky, Miroslava and Shimasaku, Kazuhiro and Caputi, Karina and Kusakabe, Haruka and Morokuma-Matsui, Kana and Shotaro, Kikuchihara and Egami, Eiichi and Lee, Minju M. and Rawle, Timothy and Espada, Daniel (2021) 'ALMA Lensing Cluster Survey: Bright [C ii] 158 μm Lines from a Multiply Imaged Sub-L⋆ Galaxy at z = 6.0719.', The Astrophysical Journal, 911 (2). p. 99.

## Abstract

We present bright [C ii] 158 μm line detections from a strongly magnified and multiply imaged (μ ∼ 20–160) sub–L* (${M}_{\mathrm{UV}}=-{19.75}_{-0.44}^{+0.55}$) Lyman-break galaxy (LBG) at z = 6.0719 ± 0.0004, drawn from the ALMA Lensing Cluster Survey (ALCS). Emission lines are identified at 268.7 GHz at ≥8σ exactly at the positions of two multiple images of the LBG, behind the massive galaxy cluster RXCJ0600−2007. Our lens models, updated with the latest spectroscopy from VLT/MUSE, indicate that a sub region of the LBG crosses the caustic, and is lensed into a long (∼6'') arc with a local magnification of μ ∼ 160, for which the [C ii] line is also significantly detected. The source plane reconstruction resolves the interstellar medium (ISM) structure, showing that the [C ii] line is co-spatial with the rest-frame UV continuum at a scale of ∼300 pc. The [C ii] line properties suggest that the LBG is a rotation-dominated system, whose velocity gradient explains a slight difference in redshifts between the whole LBG and its sub-region. The star formation rate (SFR)–L[CII] relations, for whole and sub-regions of the LBG, are consistent with those of local galaxies. We evaluate the lower limit of the faint-end of the [C ii] luminosity function at z = 6, finding it to be consistent with predictions from semi-analytical models and from the local SFR–L[CII] relation with a SFR function at z = 6. These results imply that the local SFR–L[CII] relation is universal for a wide range of scales, including the spatially resolved ISM, the whole region of the galaxy, and the cosmic scale, even in the epoch of reionization.