A massive quiescent galaxy in a group environment at $z=4.53$

Takumi Kakimoto; Masayuki Tanaka; Masato Onodera; Rhythm Shimakawa; Po-Feng Wu; Katriona M. L. Gould; Kei Ito; Shuowen Jin; Mariko Kubo; Tomoko L. Suzuki; Sune Toft; Francesco Valentino; Kiyoto Yabe

arXiv · 2308.15011

A massive quiescent galaxy in a group environment at $z=4.53$

Takumi Kakimoto·Masayuki Tanaka·Masato Onodera·Rhythm Shimakawa·Po-Feng Wu·Katriona M. L. Gould·Kei Ito·Shuowen Jin·Mariko Kubo·Tomoko L. Suzuki·Sune Toft·Francesco Valentino·Kiyoto Yabe

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Abstract

We report on the spectroscopic confirmation of a massive quiescent galaxy at $z_\mathrm{spec}=4.53$ in the COSMOS field. The object was first identified as a galaxy with suppressed star formation at $z_\mathrm{phot}\sim4.65$ from the COSMOS2020 catalog. The follow-up spectroscopy with Keck/MOSFIRE in the $K$-band reveals faint [OII] emission and the Balmer break, indicative of evolved stellar populations. We perform the spectral energy distribution fitting using photometry and spectrum to infer physical properties. The obtained stellar mass is high ($M_*\sim 10^{10.8}\,M_\odot$) and the current star formation rate is more than 1 dex below that of main-sequence galaxies at $z=4.5$. Its star formation history suggests that this galaxy experienced rapid quenching from $z\sim 5$. The galaxy is among the youngest quiescent galaxies confirmed so far at $z_\mathrm{spec}>3$ with $z_\mathrm{form}\sim5.2$ ($200\,\mathrm{Myr}$ ago), which is the epoch when 50\% of total stellar mass was formed. A unique aspect of the galaxy is that it is in an extremely dense region; there are four massive star-forming galaxies at $4.4<z_\mathrm{phot}<4.7$ located within 150 physical kpc from the galaxy. Interestingly, three of them have strongly overlapping virial radii with that of the central quiescent galaxy ($\sim 70\,\mathrm{kpc}$), suggesting that the over-density region is likely the highest redshift candidate of a dense group with a spectroscopically confirmed quiescent galaxy at the center. The group provides us with a unique opportunity to gain insights into the role of the group environment for quenching at $z\sim5$, which corresponds to the formation epoch of massive elliptical galaxies in the local Universe.

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Takumi Kakimoto, Masayuki Tanaka, Masato Onodera, Rhythm Shimakawa, Po-Feng Wu, Katriona M. L. Gould, Kei Ito, Shuowen Jin, Mariko Kubo, Tomoko L. Suzuki, Sune Toft, Francesco Valentino, Kiyoto Yabe. 2023-08-29. A massive quiescent galaxy in a group environment at $z=4.53$. https://arxiv.org/abs/2308.15011

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