The Fundamental Plane in the LEGA-C Survey: unraveling the $M/L$ variations of massive star-forming and quiescent galaxies at $z\sim0.8$

TL;DR

This study uses the LEGA-C survey to analyze the Fundamental Plane of massive galaxies at z~0.8, revealing differences in mass-to-light ratios between star-forming and quiescent galaxies and suggesting that these variations are due to stellar populations and dark matter contributions.

Contribution

It demonstrates that both star-forming and quiescent galaxies lie on the same mass Fundamental Plane at z~0.8, with differences in M/L ratios driven by stellar populations and dark matter.

Findings

Quiescent and star-forming galaxies occupy different regions in the g-band FP.

Both galaxy types lie on the same mass FP with similar scatter.

Variations in M/L are due to stellar populations and dark matter fraction.

Abstract

We explore the connection between the kinematics, structures and stellar populations of massive galaxies at $0.6<z<1.0$ using the Fundamental Plane (FP). Combining stellar kinematic data from the Large Early Galaxy Astrophysics Census (LEGA-C) survey with structural parameters measured from deep Hubble Space Telescope imaging, we obtain a sample of 1419 massive ($\log(M_*/M_\odot) >10.5$) galaxies that span a wide range in morphology, star formation activity and environment, and therefore is representative of the massive galaxy population at $z\sim0.8$. We find that quiescent and star-forming galaxies occupy the parameter space of the $g$-band FP differently and thus have different distributions in the dynamical mass-to-light ratio ($M_{\rm dyn}/L_g$), largely owing to differences in the stellar age and recent star formation history, and, to a lesser extent, the effects of dust attenuation. In contrast, we show that both star-forming and quiescent galaxies lie on the same mass FP at $z\sim 0.8$, with a comparable level of intrinsic scatter about the plane. We examine the variation in $M_{\rm dyn}/M_*$ through the thickness of the mass FP, finding no significant residual correlations with stellar population properties, S\'ersic index, or galaxy overdensity. Our results suggest that, at fixed size and velocity dispersion, the variations in $M_{\rm dyn}/L_g$ of massive galaxies reflect an approximately equal contribution of variations in $M_*/L_g$, and variations in the dark matter fraction or initial mass function.