Authors: Sugahara, Yuma; alvarez-Marquez, Javier; Hashimoto, Takuya; Colina, Luis; Inoue, Akio K.; Costantin, Luca; Fudamoto, Yoshinobu; Mawatari, Ken; Ren, Yi W.; Arribas, Santiago; Bakx, Tom J. L. C.; Blanco-Prieto, Carmen; Ceverino, Daniel; Crespo Gomez, Alejandro; Hagimoto, Masato; Hashigaya, Takeshi; Marques-Chaves, Rui; Matsuo, Hiroshi; Nakazato, Yurina; Pereira-Santaella, Miguel; Tamura, Yoichi; Usui, Mitsutaka; Yoshida, Naoki
Journal: ASTROPHYSICAL JOURNAL
Publication date: 2025/03/10
Abstract: We present JWST NIRCam imaging of B14-65666 (Big Three Dragons), a bright Lyman-break galaxy system (MUV = -22.5 mag) at z = 7.15. The high angular resolution of NIRCam reveals the complex morphology of two galaxy components: galaxy E has a compact core (E-core), surrounded by diffuse, extended, rest-frame optical emission, which is likely to be tidal tails; and galaxy W has a clumpy and elongated morphology with a blue UV slope (beta UV = -2.2 +/- 0.1). The flux excess, F356W – F444W, peaks at the E-core ( 1.05-0.09+0.08 mag), tracing the presence of strong [O iii] lambda lambda 4960,5008 emission. Atacama Large Millimeter/submillimeter Array archival data show that the bluer galaxy W is brighter in dust continua than the redder galaxy E, while the tails are bright in [O iii] 88 mu m. The UV/optical and submillimeter spectral energy distribution (SED) fitting confirms that B14-65666 is a major merger in a starburst phase as derived from the stellar mass ratio (3:1 to 2:1) and the star formation rate, similar or equal to 1 dex higher than the star formation main sequence at the same redshift. Galaxy E is a dusty (AV = 1.2 +/- 0.1 mag) starburst with a possible high dust temperature (>= 63-68 K). Galaxy W would have a low dust temperature (<= 27-33 K) or patchy stellar-and-dust geometry, as suggested by the IR excess and beta UV diagram. The high optical-to-far-IR [O iii] line ratio of the E-core shows its lower gas-phase metallicity (similar or equal to 0.2-0.4 Z circle dot) than galaxy W. These results agree with a scenario where major mergers disturb morphology and induce nuclear dusty starbursts triggered by less-enriched inflows. B14-65666 shows a picture of complex stellar buildup processes during major mergers in the epoch of reionization.
