Modeling the PanchromaticSpectral Energy Distributionsof GalaxiesCharlie ConroyDepartment of Astronomy and Astrophysics, University of California, Santa Cruz,California 95064; email: [email protected]Annu. Rev. Astron. Astrophys. 2013. 51:393–455TheAnnual Review of Astronomy and Astrophysicsisonline at astro.annualreviews.orgThis article’s doi:10.1146/annurev-astro-082812-141017Copyright c 2013 by Annual Reviews.All rights reservedKeywordsstars, abundances, dust, stellar populations, galaxies: stellar content, galaxyevolutionAbstractThe spectral energy distributions (SEDs) of galaxies are shaped by nearlyevery physical property of the system, including the star-formation history,metal content, abundance pattern, dust mass, grain size distribution, star-dust geometry, and interstellar radiation field. The principal goal of stellarpopulation synthesis (SPS) is to extract these variables from observed SEDs.In this review I provide an overview of the SPS technique and discuss whatcan be reliably measured from galaxy SEDs. Topics include stellar masses,star-formation rates and histories, metallicities and abundance patterns, dustproperties, and the stellar initial mass function.393Annu. Rev. Astron. Astrophys. 2013.51:393-455. Downloaded from Access provided by University of California - Irvine on 01/16/19. For personal use only.
Spectral energydistribution (SED):light emitted over allor a portion of theFUV-FIR spectraldomain, includingbroadband data and/ormoderate-resolutionspectraSFH:star-formationhistoryIMF:initial massfunctionFUV:far-ultravioletFIR:far-infraredNIR:near-infraredSPS:stellarpopulation synthesisAGB:asymptoticgiant branchHB:horizontalbranch1. INTRODUCTIONMany of the fundamental properties of unresolved stellar populations are encoded in their spectralenergy distributions (SEDs). These properties include the star-formation history (SFH), stellarmetallicity and abundance pattern, stellar initial mass function (IMF), total mass in stars, and thephysical state and quantity of dust and gas. Some of these properties are easier to measure thanothers, and each provides important clues regarding the formation and evolution of galaxies. It isprecisely these quantities, measured from the SEDs of galaxies, that have provided the foundationfor our modern understanding of galaxy formation and evolution.Over the past several decades considerable effort has been devoted to extracting informationfromtheSEDs ofgalaxies,exploitinginformationfromthefar-ultraviolet (FUV)tothefar-infrared(FIR). Early attempts at understanding the visible and near-infrared (NIR) spectral windowsapproached the problem by combining mixtures of stars in ad hoc ways until a match was achievedwith observations (e.g., Spinrad & Taylor 1971). More sophisticated versions of this techniquewere developed that incorporated physical constraints and automated fitting techniques (Faber1972). At approximately the same time, synthesis models were being developed that relied on stellar