The discrepancy between dynamical and stellar masses in massive compact galaxies traces non-homology

Abstract

For many massive compact galaxies, their dynamical masses ($M_{\mathrm{dyn}}\propto {\sigma }^2{r}_{\mathrm{e}}$) are lower than their stellar masses ($M_{\star }$). We analyse the unphysical mass discrepancy $M_{\star }/M_{\mathrm{dyn}}>1$ on a stellar-mass-selected sample of early-type galaxies ($M_{\star }\gtrsim 10^{11}{\mathrm{M}}_{\odot }$) at redshifts $z\sim 0.2$ to $z\sim 1.1$. We build stacked spectra for bins of redshift, size and stellar mass, obtain velocity dispersions, and infer dynamical masses using the virial relation $M_{\mathrm{dyn}}\equiv K{\sigma }_{\mathrm{e}}^2{r}_{\mathrm{e}}/G$ with $K=5.0$; this assumes homology between our galaxies and nearby massive ellipticals. Our sample is completed using literature data, including individual objects up to $z\sim 2.5$ and a large local reference sample from the Sloan Digital Sky Survey (SDSS). We find that, at all redshifts, the discrepancy between $M_{\star }$ and $M_{\mathrm{dyn}}$ grows as galaxies depart from the present-day relation between stellar mass and size: the more compact a galaxy, the larger its $M_{\star }/M_{\mathrm{dyn}}$. Current uncertainties in stellar masses cannot account for values of $M_{\star }/M_{\mathrm{dyn}}$ above 1. Our results suggest that the homology hypothesis contained in the $M_{\mathrm{dyn}}$ formula above breaks down for compact galaxies. We provide an approximation to the virial coefficient $K\sim 6.0{\left[r_{\mathrm{e}}/(3.185\mathrm{kpc})\right]}^{-0.81}{\left[M_{\star }/(10^{11}{\mathrm{M}}_{\odot })\right]}^{0.45}$, which solves the mass discrepancy problem. A rough approximation to the dynamical mass is given by $M_{\mathrm{dyn}}\sim {\left[{\sigma }_{\mathrm{e}}/(200\mathrm{km}{\mathrm{s}}^{-1})\right]}^{3.6}{\left[r_{\mathrm{e}}/(3\mathrm{kpc})\right]}^{0.35}2.1\times 10^{11}{\mathrm{M}}_{\odot }$.

15 pages, 15 figures, 2 tables. Updated to match the published version in MNRAS

References in corpus (17)

• Astropy: A Community Python Package for Astronomy
• The propagation of uncertainties in stellar population synthesis modeling I: The relevance of uncertain aspects of stellar evolution and the IMF to the derived physical properties of galaxies
• K-corrections and filter transformations in the ultraviolet, optical, and near infrared
• A systematic variation of the stellar initial mass function in early-type galaxies
• The All-wavelength Extended Groth Strip International Survey (AEGIS) Data Sets
• Size evolution of the most massive galaxies at 1.7<z<3 from GOODS NICMOS survey imaging
• An Over-Massive Black Hole in the Compact Lenticular Galaxy NGC1277
• Superdense massive galaxies in the Nearby Universe
• Dynamical masses of early-type galaxies at z~2: Are they truly superdense?
• The Kormendy relation of massive elliptical galaxies at z~1.5. Evidence for size evolution ?
• NGC1277: a massive compact relic galaxy in the nearby Universe
• Velocity Dispersions and Dynamical Masses for a Large Sample of Quiescent Galaxies at z > 1: Improved Measures of the Growth in Mass and Size
• Stellar mass estimates in early-type galaxies: procedures, uncertainties and models dependence
• Clusters at Half Hubble Time: Galaxy Structure and Colors in RXJ0152.7-1357 and MS1054-03
• New release of the ELODIE library: Version 3.1
• SINFONI/VLT 3D spectroscopy of massive galaxies: Evidence of rotational support at z~1.4
• A Search for Moderate-Redshift Survivors from the Population of Luminous Compact Passive Galaxies at High Redshift

Cited by in corpus (13)

• MOSFIRE Spectroscopy of Quiescent Galaxies at 1.5 < z < 2.5. I - Evolution of Structural and Dynamical Properties
• Keck-I MOSFIRE spectroscopy of compact star-forming galaxies at z$\gtrsim$2: High velocity dispersions in progenitors of compact quiescent galaxies
• Caught in the act: gas and stellar velocity dispersions in a fast quenching compact star-forming galaxy at z~1.7
• Revisiting the bulge-halo conspiracy I: Dependence on galaxy properties and halo mass
• Dynamical Models of Elliptical Galaxies -- I. Simple Methods
• Stellar populations of galaxies in the ALHAMBRA survey up to $z\sim 1$. IV. Properties of quiescent galaxies on the stellar mass$-$size plane
• Constraints on the HI Mass of NGC 1052-DF2
• Evaluating Galaxy Dynamical Masses From Kinematics and Jeans Equilibrium in Simulations
• Compact Quiescent Galaxies at Intermediate Redshifts
• Dynamical masses and non-homology of massive elliptical galaxies grown by dry mergers
• The most massive galaxies in clusters are already fully grown at $z\sim 0.5$
• Constraints on the evolutionary mechanisms of massive galaxies since $z\sim 1$ from their velocity dispersions
• Star-forming Galaxies in Intermediate Redshift Clusters: Stellar vs. Dynamical Masses of Luminous Compact Blue Galaxies