Stellar Velocity Dispersion of a Massive Quenching Galaxy at z = 4.01
Stellar Velocity Dispersion of a Massive Quenching Galaxy at z = 4.01
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DOI：
10.3847/2041-8213/ab4ff3
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发表时间：
2019-09
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通讯作者：
Masayuki Tanaka;F. Valentino;S. Toft;M. Onodera;R. Shimakawa;D. Ceverino;A. Faisst;A. Gallazzi;C. Gómez-Guijarro;M. Kubo;G. Magdis;C. Steinhardt;M. Stockmann;K. Yabe;J. Zabl
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文献类型：
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作者：
Masayuki Tanaka;F. Valentino;S. Toft;M. Onodera;R. Shimakawa;D. Ceverino;A. Faisst;A. Gallazzi;C. Gómez-Guijarro;M. Kubo;G. Magdis;C. Steinhardt;M. Stockmann;K. Yabe;J. Zabl
我们给出了一个质量猝灭星系在z=4时的恒星速度色散测量结果。该星系首次被确认为一个大质量z≥4星系，它的恒星形成受到抑制，这是基于深部多波段数据的光度红移。在Keck上用MOSFIRE进行的后续光谱观测显示了强烈的多重吸收特征，这些特征被识别为巴尔默线，给出了z=4.01的安全红移。这是迄今已知的最遥远的静止星系。由于光谱的高S/N，我们能够估计恒星的速度色散，这比以前在z=2.8时的最高红移测量有了很大的飞跃。有趣的是，我们发现速度色散与今天大质量星系的速度色散是一致的，这意味着在过去的12年里，速度色散没有显著的变化。根据深部光学图像(Reff<；1.3kpc)对其物理尺寸的严格上限，我们发现它的动力学质量与从光度学推断的恒星质量是一致的。此外，该星系位于低红移星系外推的质量基准面上。在σ中观察到的没有强烈的演化表明，大质量星系核心的质量并没有显著演化，而大部分质量增长发生在星系的外围，这也增加了星系的大小。这张图片与两个阶段的形成情景是一致的，在这个情景中，质量和大小的增长是通过合并在星系外围吸积而成的。我们的结果表明，第一阶段最早可能在z∼4完成。
We present the first stellar velocity dispersion measurement of a massive quenching galaxy at z = 4. The galaxy is first identified as a massive z ≥ 4 galaxy with suppressed star formation from photometric redshifts based on deep multiband data. A follow-up spectroscopic observation with MOSFIRE on Keck revealed strong multiple absorption features, which are identified as Balmer lines, giving a secure redshift of z = 4.01. This is the most distant quiescent galaxy known to date. Thanks to the high S/N of the spectrum, we are able to estimate the stellar velocity dispersion, , making a significant leap from the previous highest redshift measurement at z = 2.8. Interestingly, we find that the velocity dispersion is consistent with that of massive galaxies today, implying no significant evolution in velocity dispersion over the last 12 Gyr. Based on a stringent upper limit on its physical size from deep optical images (reff < 1.3 kpc), we find that its dynamical mass is consistent with the stellar mass inferred from photometry. Furthermore, the galaxy is located on the mass fundamental plane extrapolated from lower redshift galaxies. The observed no strong evolution in σ suggests that the mass in the core of massive galaxies does not evolve significantly, while most of the mass growth occurs in the outskirts of the galaxies, which also increases the size. This picture is consistent with a two-phase formation scenario in which mass and size growth is due to accretion in the outskirts of galaxies via mergers. Our results imply that the first phase may be completed as early as z ∼ 4.