The Mass Scale of High-Redshift Galaxies: Virial Mass Estimates Calibrated with Stellar Dynamical Models from LEGA-C

Abstract

Dynamical models for $673$ galaxies at $z=0.6-1.0$ with spatially resolved (long-slit) stellar kinematic data from LEGA-C are used to calibrate virial mass estimates defined as $M_{\mathrm{vir}}=K{\sigma }_{\star ,\mathrm{int}}^{\prime 2}R$, with $K$ a scaling factor, ${\sigma }_{\star ,\mathrm{int}}^{\prime }$ the spatially-integrated stellar velocity second moment from the LEGA-C survey and $R$ the effective radius measured from a Sérsic profile fit to HST imaging. The sample is representative for $M_{\star }>3\times 10^{10}{M}_{\odot }$ and includes all types of galaxies, irrespective of morphology and color. We demonstrate that using $R=R_{\mathrm{sma}}$~(the semi-major axis length of the ellipse that encloses 50\% of the light) in combination with an inclination correction on ${\sigma }_{\star ,\mathrm{int}}^{\prime }$~produces an unbiased $M_{\mathrm{vir}}$. We confirm the importance of projection effects on ${\sigma }_{\star ,\mathrm{int}}^{\prime }$ by showing the existence of a similar residual trend between virial mass estimates and inclination for the nearby early-type galaxies in the ATLAS${}^{3D}$~survey. Also, as previously shown, when using a Sérsic profile-based $R$ estimate, then a Sérsic index-dependent correction to account for non-homology in the radial profiles is required. With respect to analogous dynamical models for low-redshift galaxies from the ATLAS${}^{3D}$~survey we find a systematic offset of 0.1 dex in the calibrated virial constant for LEGA-C, which may be due to physical differences between the galaxy samples or an unknown systematic error. Either way, with our work we establish a common mass scale for galaxies across 8 Gyr of cosmic time with a systematic uncertainty of at most 0.1 dex.

Published in ApJ

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