The Relationship between Stellar Light Distributions of Galaxies and Their Formation Histories

By Christopher J. Conselice. 2003

651 citations recorded by the source corpus.

A major problem in extragalactic astronomy is the inability to distinguish in a robust, physical, and model-independent way how galaxy populations are physically related to each other and to their formation histories. A similar, but distinct, and also long-standing question is whether the structural appearances of galaxies, as seen through their stellar light distributions, contain enough physical information to offer this classification. We argue through the use of 240 images of nearby galaxies that three model-independent parameters measured on a single galaxy image reveal its major ongoing and past formation modes and can be used as a robust classification system. These parameters quantitatively measure: the concentration (C), asymmetry (A), and clumpiness (S) of a galaxy's stellar light distribution. When combined into a three-dimensional "CAS" volume all major classes of galaxies in various phases of evolution are cleanly distinguished. We argue that these three parameters correlate with important modes of galaxy evolution: star formation and major merging activity. This is argued through the strong correlation of Hα equivalent width and broadband colors with the clumpiness parameter S, the uniquely large asymmetries of 66 galaxies undergoing mergers, and the correlation of bulge to total light ratios, and stellar masses, with the concentration index. As an obvious goal is to use this system at high redshifts to trace evolution, we demonstrate that these parameters can be measured, within a reasonable and quantifiable uncertainty with available data out to z ∼ 3 using the Hubble Space Telescope GOODS ACS and Hubble Deep Field images.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/4acb34c57395d4caec74e617e8f0fdfac64c2937

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Citations in the corpus

THE MAJOR AND MINOR GALAXY MERGER RATES AT z < 1.5 (2011, background): “…asymmetry (A) picks out large-scale high surface brightness asymmetric structures (e.g. Abraham et al. 1994; Conselice, Bershady, & Jangren 2000; Conselice 2003); the combination of the Gini coefficient (G; Abraham et al. 2003; Lotz et al. 2004) and second-order moment of the brightest 20% of…”
The optical morphologies of galaxies in the IllustrisTNG simulation: a comparison to Pan-STARRS observations (2018, methodology): “…IDL code described in Lotz et al. (2004, 2006, 2008a,b) for calculating the Gini–M20 (Lotz et al. 2004) and concentration–asymmetry– smoothness (CAS, Conselice 2003) statistics, with some additional features such as calculating multimode–intensity–deviation statistics (MID, Freeman et al. 2013)…”
The ATLAS3D project - XXIX. The new look of early-type galaxies and surrounding fields disclosed by extremely deep optical images (2014, methodology): “Automatic algorithm parametrizing galaxies with coefficients such as the CAS (Conselice 2003), Gini (Abraham et al. 2003), or M20 (Lotz et al. 2004), have been widely used for morphological classification of large number of galaxies, especially distant ones.”
The Luminosity, Stellar Mass, and Number Density Evolution of Field Galaxies of Known Morphology from z = 0.5 to 3 (2004, methodology): “This is analogous to the color-asymmetry relationship and its outlier method of identifying major mergers (Conselice et al. 2000a; Conselice et al. 2000b; Conselice 2003; Conselice et al. 2003a).”
Morphologies of z ∼ 0.7 AGN host galaxies in CANDELS: no trend of merger incidence with AGN luminosity (2014, methodology): “For quantitative morphology measurements, we use asymmetry A which is part of the compactness–asymmetry–smoothness (CAS) classification system (Conselice 2003).”
Physical properties and environments of nearby galaxies (2009, methodology): “Other approaches have used a combination of measured parameters, for example, concentration (Abraham et al. 1994), asymmetry (Schade et al. 1995) and smoothness (Conselice 2003; Yamauchi et al. 2005).”
Total Galaxy Magnitudes and Effective Radii from Petrosian Magnitudes and Radii (2005, methodology): “While the corrective scheme outlined here is general to any choice of Petrosian index and aperture, the tabulated values we have provided are specific to two commonly used Petrosian systems, namely that used by CAS (Conselice 2003) and the setup adopted by the SDSS collaboration (York et al. 2000).”
Passively Evolving Early-Type Galaxies at 1.4 ≲ z ≲ 2.5 in the Hubble Ultra Deep Field (2005, positive): “In general, these objects occupy a range of values consistent with those of early-type galaxies; for example, all have concentrations C > 2:6, a value marking the boundary between earlyand late-type galaxies in the local universe (Strateva et al. 2001; see also Conselice 2003).”
MegaMorph - multiwavelength measurement of galaxy structure: complete Sersic profile information from modern surveys (2012, background): “One widely used parameter is the concentration index, which is defined as the ratio of the radii containing two fractions of the total flux, e.g.,C = r90/r50 (Strateva et al. 2001) orC = 5 · log(r80/r20) (as defined by CAS, Conselice 2003).”
Early and Rapid Merging as a Formation Mechanism of Massive Galaxies: Empirical Constraints (2005, methodology): “However, galaxies dominated by star formation, and which are not merging, have large clumpiness and asymmetry values because the light is distributed in localized and compact star forming complexes (Conselice 2003b; Mobasher et al. 2004).”
Galaxy Zoo: the dependence of morphology and colour on environment (2008, background): “…avenues to more sophisticated automatic morphologies, some which use physical insight or statistical methods to naturally classify galaxies, while others aim todirectly reproduce classifications by professional astronomers (e.g. Lahav et al. 1995; Simard et al. 2002; Conselice 2003; Goto etal.”
Galaxy Zoo: the properties of merging galaxies in the nearby Universe – local environments, colours, masses, star formation rates and AGN activity (2009, background): “Similarly, locating mergers via structural parameters such as concentration and asymmetry (Conselice 2003) is problematic due to the great variety of configurations of mergers (progenitor types, impact parameters and the stage at which the system is viewed) making it difficult to define a parameter…”
THE RISE AND FALL OF PASSIVE DISK GALAXIES: MORPHOLOGICAL EVOLUTION ALONG THE RED SEQUENCE REVEALED BY COSMOS (2009, methodology): “It is well known, however, that techniques such as CAS (e.g., Conselice 2003) or Gini/M20 (see Abraham et al. 2007) often disagree when compared to visual morphologies and can differ from each other.”
The structures of distant galaxies – III. The merger history of over 20 000 massive galaxies at z < 1.2 (2008, methodology): “This particular measurement of the concentration correlates well with the mass and halo properties of galaxies in the nearby universe (e.g., Bershady et al. 2000; Conselice 2003).”
Resolved Galaxies in the Hubble Ultra Deep Field: Star Formation in Disks at High Redshift (2007, background): “Conselice (2003), Menanteau et al. (2006), and others show there is a correlation between the asymmetry and concentration value of a galaxy and the Hubble classification as a spiral, elliptical/S0, or Irr/peculiar.”
CO excitation of normal star forming galaxies out to $z=1.5$ as regulated by the properties of their interstellar medium (2014, background): “…the original images a smoothed version – obtained through a boxcar averaging with a kernel size equal to 20% the Kron radius – and by evaluating the normalized flux in those pixels with an intensity larger than 3× the background standard deviation (see, e.g., Conselice 2003; Cibinel et al 2013).”
Lensing and x-ray mass estimates of clusters (simulations) (2012, background): “Zhang et al. (2010) and Okabe et al. (2010) (Locuss collaboration) considered the asymmetry and fluctuation parameters as introduced by Conselice (2003).”
The Evolution of Galaxy Structure Over Cosmic Time (2014, methodology): “While the contamination from non-mergers is fairly low at a few percent, the fraction of actual mergers which are identified is roughly 50% (Conselice 2003).”
The Assembly of Diversity in the Morphologies and Stellar Populations of High-Redshift Galaxies (2005, background): “For example, Abraham et al. (1999) and Conselice et al. (2003) have shown that galaxy morphological type is generally distinguished by their concentration and asymmetry indexes (see also Conselice 2003).”
SUPERDENSE MASSIVE GALAXIES IN WINGS LOCAL CLUSTERS (2009, methodology): “Our approach is a generalization of the nonparametric method proposed by Conselice et al. (2000) (see also, Conselice 2003).”