Early steps in the hierarchical assembly of a Milky Way-mass galaxy 1 Gyr after the Big Bang
Abstract
We report JWST observations of a zspec=5.196 compact group of three strongly lensed low-mass galaxies (M⋆ ∼ 106−7 M⊙ each) whose small line-of-sight velocity offsets (from −120±100 to +160±110 km s−1) and projected separations (∼2 kpc) suggest that they are undergoing merging. On the basis of abundance-matching arguments, the trio appear to be destined to evolve into a Milky Way-mass galaxy by the present day. Our spectrophotometric analysis suggests that the stellar mass growth of this system is not simply just due to the merging of its components; rather, it is being dramatically enhanced by intense bursts of star formation. Presumably initiated by tidally-induced gas inflows, these star-forming bursts boost the mass growth 2.6±0.5 times that expected in straightforward merging of the existing stellar masses. These spectroscopic observations thus not only demonstrate that hierarchical assembly remains a viable formation channel in the early assembly phases of present-day massive galaxy, but also that interaction-induced bursts of star formation are a major accelerator of this assembly process.
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BibTeX
@misc{asada2026early,
title = {{Early steps in the hierarchical assembly of a Milky Way-mass galaxy 1 Gyr after the Big Bang}},
author = {Yoshihisa Asada and Marcin Sawicki and Guillaume Desprez and Jon Judez and Marusa Bradac and Kartheik Iyer and Nicholas S. Martis and Adam Muzzin and Gael Noirot and Ghassan T. E. Sarrouh and Chris J. Willott and Jacqueline Antwi-Danso and Seiji Fujimoto and Danilo Marchesini and Vladan Markov and Luke Robbins and Visal Sok},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.19687},
eprint = {2609.19687},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.19687},
}
RIS
TY - UNPB
TI - Early steps in the hierarchical assembly of a Milky Way-mass galaxy 1 Gyr after the Big Bang
AU - Yoshihisa Asada
AU - Marcin Sawicki
AU - Guillaume Desprez
AU - Jon Judez
AU - Marusa Bradac
AU - Kartheik Iyer
AU - Nicholas S. Martis
AU - Adam Muzzin
AU - Gael Noirot
AU - Ghassan T. E. Sarrouh
AU - Chris J. Willott
AU - Jacqueline Antwi-Danso
AU - Seiji Fujimoto
AU - Danilo Marchesini
AU - Vladan Markov
AU - Luke Robbins
AU - Visal Sok
PY - 2026
DA - 2026/09/17
PB - arXiv
DO - 10.48550/arxiv.2609.19687
UR - https://arxiv.org/abs/2609.19687
AB - We report JWST observations of a z_spec=5.196 compact group of three strongly lensed low-mass galaxies (M_⋆ ∼ 10^6−7 M_⊙ each) whose small line-of-sight velocity offsets (from −120±100 to +160±110 km s^−1) and projected separations (∼2 kpc) suggest that they are undergoing merging. On the basis of abundance-matching arguments, the trio appear to be destined to evolve into a Milky Way-mass galaxy by the present day. Our spectrophotometric analysis suggests that the stellar mass growth of this system is not simply just due to the merging of its components; rather, it is being dramatically enhanced by intense bursts of star formation. Presumably initiated by tidally-induced gas inflows, these star-forming bursts boost the mass growth 2.6±0.5 times that expected in straightforward merging of the existing stellar masses. These spectroscopic observations thus not only demonstrate that hierarchical assembly remains a viable formation channel in the early assembly phases of present-day massive galaxy, but also that interaction-induced bursts of star formation are a major accelerator of this assembly process.
ER -