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| Sérsic profile | |
|---|---|
| Name | Sérsic profile |
| Author | José Luis Sérsic |
| Year | 1963 |
| Field | Astronomy |
Sérsic profile is an analytic function used to describe how the surface brightness of astronomical objects varies with radius. It generalizes several empirical models and is widely applied in studies of Andromeda Galaxy, Milky Way, Hubble Space Telescope, Sloan Digital Sky Survey, and galaxy morphology across samples from Local Group to deep fields like the Hubble Deep Field and COSMOS survey. The profile's flexibility makes it central to analyses by groups at institutions such as European Southern Observatory, Space Telescope Science Institute, Max Planck Institute for Astronomy, Harvard–Smithsonian Center for Astrophysics, and surveys like Large Synoptic Survey Telescope (now Vera C. Rubin Observatory).
The Sérsic profile is defined by an exponential-like formula that gives surface brightness I(R) as a function of projected radius R, characterized by a scale intensity I_e at effective radius R_e and a dimensionless index n. Its mathematical form connects to earlier functions used by Edwin Hubble and Gérard de Vaucouleurs, and is frequently written with a constant b_n chosen so that R_e encloses half of the total light. Variants of the formula are implemented in software from teams at European Southern Observatory, National Optical Astronomy Observatory, Astropy Project, and packages developed by groups at University of Cambridge and Massachusetts Institute of Technology.
The profile traces to empirical descriptions of galaxy photometry in mid-20th-century work by observers associated with observatories like Mount Wilson Observatory and Palomar Observatory and was formalized by José Luis Sérsic while building on results from Gérard de Vaucouleurs, Edwin Hubble, and earlier catalogs such as those by Harlow Shapley. Development continued through studies at California Institute of Technology, Carnegie Institution for Science, and collaborations involving Royal Observatory, Edinburgh and Institut d'Astrophysique de Paris analysts who refined the index n to capture bulge and disk distinctions used in morphological classification schemes influenced by Hubble sequence and work by Allan Sandage.
Key parameters are the effective radius R_e, effective intensity I_e (or surface brightness μ_e), and the Sérsic index n. Special cases include the exponential profile (n = 1) often used for disks studied in Andromeda Galaxy and Triangulum Galaxy, and the de Vaucouleurs profile (n = 4) applied to elliptical galaxies cataloged in surveys by Two Micron All Sky Survey and Sloan Digital Sky Survey. The parameter b_n depends on n and is tabulated in works produced by researchers at European Space Agency and computational groups at University of Oxford.
Physically, the index n correlates with structural properties of galaxies, linking bulge prominence in systems like Sombrero Galaxy and M87 to formation histories invoked in simulations from Illustris project and EAGLE simulation. Applications include bulge–disk decomposition in studies by teams at University of California, Santa Cruz and Johns Hopkins University, lens-modeling by groups connected to Max Planck Institute for Astrophysics and Kavli Institute for Cosmology, and surface photometry for clusters cataloged by Abell catalog and programs at National Radio Astronomy Observatory. The profile informs scaling relations such as the Fundamental Plane used by researchers at European Southern Observatory and Carnegie Observatories.
Fitting techniques employ non-linear least-squares, Markov chain Monte Carlo algorithms developed at Princeton University and University College London, and forward-modeling used in pipelines at Space Telescope Science Institute and Subaru Telescope teams. Tools include two-dimensional fitting codes from groups at Institut d'Astrophysique de Paris and community software like those maintained by Astropy Project and developers affiliated with University of Toronto. Estimators account for point-spread functions characterized at Keck Observatory and Very Large Telescope and statistical practices referenced in work from Max Planck Institute for Astronomy.
Limitations arise from deviations in profile wings, multi-component systems in galaxies studied by Yale University and University of Arizona, and environmental effects reported in cluster surveys by European Southern Observatory and Kitt Peak National Observatory. Modifications include core-Sérsic prescriptions introduced by researchers at University of Cambridge and truncation/anti-truncation models applied in analyses by Observatoire de Paris and simulation comparisons from Millennium Simulation teams. Hybrid decompositions combine Sérsic components with exponential disks in catalogs produced by Sloan Digital Sky Survey collaborations.
Empirical fits show disks of spiral galaxies such as NGC 628 often have n ≈ 1, while giant ellipticals like NGC 4874 and central cluster galaxies examined in Coma Cluster surveys exhibit n > 4. Studies of local dwarfs cataloged by Local Group researchers and programs at Carnegie Institution for Science report lower n values, whereas brightest cluster galaxies analyzed with Hubble Space Telescope imaging display high n and extended envelopes. Large compilations from Sloan Digital Sky Survey, Two Micron All Sky Survey, and deep field programs like GOODS provide statistical distributions of n, R_e, and μ_e used by groups at Harvard–Smithsonian Center for Astrophysics and Max Planck Institute for Astronomy to constrain models of galaxy evolution.
Category:Galaxy photometry