Stellar Velocity Dispersion of a Massive Quenching Galaxy at z=4.01

TL;DR

This study measures the stellar velocity dispersion of a massive quenching galaxy at z=4.01, revealing that its core mass properties are similar to present-day galaxies, supporting a two-phase formation model.

Contribution

First measurement of stellar velocity dispersion in a quenching galaxy at z=4.01, providing insights into galaxy evolution over 12 billion years.

Findings

Velocity dispersion is consistent with local massive galaxies.

Galaxy's dynamical mass aligns with stellar mass estimates.

Velocity dispersion shows little evolution with redshift.

Abstract

We present the first stellar velocity dispersion measurement of a massive quenching galaxy at z=4.01. The galaxy is first identified as a massive z>~4 galaxy with suppressed star formation from photometric redshifts based on deep multi-band data in the UKIDSS Ultra Deep Survey field. A follow-up spectroscopic observation with MOSFIRE on Keck revealed strong multiple absorption features, which are identified as Balmer absorption lines, giving a secure redshift of z=4.01. Thanks to the high S/N of the spectrum, we are able to estimate the stellar velocity dispersion, sigma=268+/-59 km/s. This velocity dispersion is consistent with that of massive galaxies today, implying no significant evolution in stellar velocity dispersion over the last 12 Gyr. Based on an upper limit on its physical size from deep optical images (r_eff<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. Combining all these results, we find that the velocity dispersion does not significantly evolve with redshift, although the size and mass of massive quenched galaxies do. This 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.