$R_{\mathrm{e}}$. I. Understanding galaxy sizes, associated luminosity densities, and the artificial division of the early-type galaxy population

Abstract

The deceptive simplicity of the radius enclosing an arbitrary 50 percent of a galaxy's light has hamstrung the understanding of early-type galaxies (ETGs). Half a century ago, using the "effective half-light radii" $R_e$ from de Vaucouleurs' $R^{1/4}$ model, Sérsic reported that bright ETGs follow the relation ${\mathfrak{M}}_B\propto 2.5\log R_e$; and consequently one has that $⟨\mu {⟩}_e\propto 2.5\log R_e$ and ${\mu }_e\propto 2.5\log R_e$, where ${\mu }_e$ and $⟨\mu {⟩}_e$ are the effective surface brightness at $R_e$ and the mean effective surface brightness within $R_e$, respectively. Sérsic additionally observed an apparent transition which led him to advocate for a division between what he called dwarf and giant ETGs; a belief frequently restated to occur at ${\mathfrak{M}}_B\approx -18$ mag or Sérsic $n\approx 2.5$. Here, the location of this false dichotomy is shown to change by more than 3 mag simply depending on the arbitrary percentage of light used to quantify a galaxy's size, voiding claims for different formation physics operating on ETGs brighter and fainter than ${\mathfrak{M}}_B\approx -18$ mag. This is of further importance because quantities such as dynamical mass ${\sigma }^{2}R/G$, gravitational binding energy $G{M}^2/R$, acceleration $GM/R^2$, and the "Fundamental Plane" depend systematically on the arbitrary percentage of light used to define $R$, with implications for dark matter estimates, galaxy formation theories, compact massive galaxies, studies of peculiar velocity flows, and more. Finally, some of the vast literature which has advocated for segregating the ETG population at ${\mathfrak{M}}_B\approx -18$ mag ($M\approx 1$-$2\times 10^{10}{M}_{\odot }$) is addressed, and it is revealed how this pervasive mindset has spilled-over to influence both the classical bulge versus pseudobulge debate and recently also correlations involving supermassive black hole masses.

28 pages (including 18 figures), plus 340 references (now further updated)

References in corpus (45)

• The EAGLE project: Simulating the evolution and assembly of galaxies and their environments
• Introducing the Illustris Project: Simulating the coevolution of dark and visible matter in the Universe
• The Co-Evolution of Galaxies and Supermassive Black Holes: Insights from Surveys of the Contemporary Universe
• A Semi-Analytic Model for the Co-evolution of Galaxies, Black Holes, and Active Galactic Nuclei
• Introducing the Illustris Project: the evolution of galaxy populations across cosmic time
• Galaxy Zoo: the dependence of morphology and colour on environment
• Cold gas accretion in galaxies
• The ACS Virgo Cluster Survey. VIII. The Nuclei of Early-Type Galaxies
• Structural Properties of Pseudo-Bulges, Classical Bulges and Elliptical Galaxies: an SDSS Perspective
• Neutral hydrogen in nearby elliptical and lenticular galaxies: the continuing formation of early-type galaxies
• Unification of the Fundamental Plane and Super-Massive Black Holes Masses
• The origin of dwarf ellipticals in the Virgo cluster
• Virgo cluster early-type dwarf galaxies with the Sloan Digital Sky Survey. I. On the possible disk nature of bright early-type dwarfs
• A refined sub-grid model for black hole accretion and AGN feedback in large cosmological simulations
• Curvature in the scaling relations of early-type galaxies
• The Black Hole Mass Scale of Classical and Pseudo Bulges in Active Galaxies
• Intracluster light and the extended stellar envelopes of cD galaxies: An analytical description
• Resurrecting the Red from the Dead: Optical Properties of BCGs in X-ray Luminous Clusters
• The ACS Fornax Cluster Survey. II. The Central Brightness Profiles of Early-Type Galaxies: A Characteristic Radius on Nuclear Scales and the Transition from Central Luminosity Deficit to Excess
• Uniting Old Stellar Systems: From Globular Clusters to Giant Ellipticals
• The 6dF Galaxy Velocity Survey: Cosmological constraints from the velocity power spectrum
• The SAURON project - XI. Stellar Populations from Absorption Line Strength Maps of 24 Early-Type Spirals
• The Near-infrared S0 Survey III: Morphology of 15 Southern Early-type Disk Galaxies
• The Cluster Velocity Dispersion of the Abell 2199 cD Halo of NGC 6166
• The early-type dwarf galaxy population of the Hydra I cluster
• Revised Filter Profiles and Zero Points for Broadband Photometry
• Hiding in plain sight: An abundance of compact massive spheroids in the local Universe
• Relations Between the Sizes of Galaxies and their Dark Matter Halos at Redshifts $0<z<3$
• Stellar Kinematics and Structural Properties of Virgo Cluster Dwarf Early-Type Galaxies from the SMAKCED Project III. Rotation versus Pressure Support
• Distribution of Slow and Fast Rotators in the Fornax Cluster
• The early-type dwarf galaxy population of the Centaurus cluster
• Seeding Black Holes in Cosmological Simulations
• Keck spectroscopy of the faint dwarf elliptical galaxy population in the Perseus Cluster core: mixed stellar populations and a flat luminosity function
• Measuring supermassive black holes with gas kinematics: the active S0 galaxy NGC 3998
• Isolated compact elliptical galaxies: Stellar systems that ran away
• Implications for the origin of dwarf early-type galaxies: a detailed look at the isolated rotating dwarf early-type galaxy CG 611, with ramifications for the Fundamental Plane's (S_K)^2 kinematic scaling and the spin-ellipticity diagram
• The Nature of Blue Early-Type Galaxies in the Goods Fields
• Dwarf galaxies in the Perseus Cluster: further evidence for a disc origin for dwarf ellipticals
• Disky elliptical galaxies and the allegedly over-massive black hole in the compact massive `ES' galaxy NGC 1271
• A SuperMassive Black Hole Fundamental Plane for Ellipticals
• Galaxy And Mass Assembly (GAMA): Galaxy colour gradients versus colour, structure and luminosity
• Star Formation in Simulated Galaxies: Understanding the Transition to Quiescence at $3\times 10^{10}$ M${}_{\odot }$
• Realistic triaxial density--potential--force profiles for stellar systems and dark matter halos
• The Magnitude-Diameter Relation of Galaxies
• Comparison of simple mass estimators for slowly rotating elliptical galaxies

Cited by in corpus (12)

• A physically motivated definition for the size of galaxies in an era of ultra-deep imaging
• Extending the evolution of the stellar mass-size relation at $z\le 2$ to low stellar mass galaxies from HFF and CANDELS
• The Weak Lensing Radial Acceleration Relation: Constraining Modified Gravity and Cold Dark Matter theories with KiDS-1000
• Formation of the largest galactic cores through binary scouring and gravitational wave recoil
• Defining the (Black Hole)-Spheroid Connection with the Discovery of Morphology-Dependent Substructure in the $M_{\mathrm{BH}}$--${\mathrm{n}}_{\mathrm{sph}}$ and $M_{\mathrm{BH}}$--${\mathrm{R}}_{\mathrm{e},\mathrm{sph}}$ Diagrams: New Tests for Advanced Theories and Realistic Simulations
• Stellar masses, sizes, and radial profiles for 465 nearby early-type galaxies: an extension to the Spitzer Survey of Stellar Structure in Galaxies (S${}^4$G)
• A consistency-test for determining whether ultra-compact dwarf galaxies could be the remnant nuclei of threshed galaxies
• Resequencing the Hubble sequence and the quadratic (black hole mass)-(spheroid stellar mass) relation for elliptical galaxies
• Measuring Dark Matter in Galaxies: The Mass Fraction Within 5 Effective Radii
• The Activation of Galactic Nuclei and Their Accretion Rates are Linked to the Star Formation Rates and Bulge-types of Their Host Galaxies
• A possible signature of the influence of tidal perturbations in dwarf galaxy scaling relations
• An Escaping Outflow in a Galaxy with an Intermediate-mass Black Hole