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Dust in the Galactic Environment (Third Edition) AAS Editor in Chief Ethan Vishniac, Johns Hopkins University, Maryland, USA About the program: AAS-IOP Astronomy ebooks is the ofﬁcial book program of the American Astronomical Society (AAS) and aims to share in depth the most fascinating areas of astronomy, astrophysics, solar physics, and planetary science. The program includes publications in the following topics: Books in the program range in level from short introductory texts on fast-moving areas, graduate and upper-level undergraduate textbooks, research monographs, and practical handbooks. For a complete list of published and forthcoming titles, please visit iopscience.org/ books/aas. About the American Astronomical Society The American Astronomical Society (aas.org), established 1899, is the major organization of professional astronomers in North America. The membership (∼7,000) also includes physicists, mathematicians, geologists, engineers, and others whose research interests lie within the broad spectrum of subjects now comprising the contemporary astronomical sciences. The mission of the Society is to enhance and share humanity’s scientiﬁc understanding of the universe. Editorial Advisory Board Steve Kawaler Joan Najita Iowa State University, USA National Optical Astronomy Observatory, USA Ethan Vishniac Johns Hopkins University, USA Stacy Palen Weber State University, USA Dieter Hartmann Clemson University, USA Jason Barnes University of Idaho, USA Piet Martens Georgia State University, USA James Cordes Cornell University, USA Dawn Gelino NASA Exoplanet Science Institute, Caltech, USA Dust in the Galactic Environment (Third Edition) D C B Whittet Rensselaer Polytechnic Institute, Troy, New York, USA IOP Publishing, Bristol, UK ªIOPPublishingLtd2022 Allrightsreserved.Nopartofthispublicationmaybereproduced,storedinaretrievalsystem ortransmittedinanyformorbyanymeans,electronic,mechanical,photocopying,recording orotherwise,withoutthepriorpermissionofthepublisher,orasexpresslypermittedbylawor undertermsagreedwiththeappropriaterightsorganization.Multiplecopyingispermittedin accordancewiththetermsoflicencesissuedbytheCopyrightLicensingAgency,theCopyright ClearanceCentreandotherreproductionrightsorganizations. PermissiontomakeuseofIOPPublishingcontentotherthanassetoutabovemaybesought [email protected]. DCBWhittethasassertedhisrighttobeidentifiedastheauthorofthisworkinaccordancewith sections77and78oftheCopyright,DesignsandPatentsAct1988. ISBN 978-0-7503-3275-0(ebook) ISBN 978-0-7503-3273-6(print) ISBN 978-0-7503-3276-7(myPrint) ISBN 978-0-7503-3274-3(mobi) DOI 10.1088/2514-3433/ac7204 Version:20220901 AAS–IOPAstronomy ISSN2514-3433(online) ISSN2515-141X(print) BritishLibraryCataloguing-in-PublicationData:Acataloguerecordforthisbookisavailable fromtheBritishLibrary. PublishedbyIOPPublishing,whollyownedbyTheInstituteofPhysics,London IOPPublishing,TempleCircus,TempleWay,Bristol,BS16HG,UK USOffice:IOPPublishing,Inc.,190NorthIndependenceMallWest,Suite601,Philadelphia, PA19106,USA Coverimage:SkiesaboveESO’sParanalObservatory.Imagecredit:ESO/P.Horálek. To my grandson, Edward (b. 2019). May he and his generation inherit a habitable world. Contents Preface xv Acknowledgments xvi Author biography xvii 1 Astrophysical Dust: An Overview 1-1 1.1 Introduction 1-1 1.2 Methods of Investigation 1-3 1.2.1 Interstellar Extinction 1-4 1.2.2 The Reddening of Starlight 1-5 1.2.3 New Light in the Infrared 1-7 1.2.4 Interstellar Polarization 1-8 1.2.5 Spectral Features 1-8 1.2.6 Where the Atoms Went 1-9 1.2.7 Gathering It All Together: Mathematical Models 1-10 1.3 Interstellar Environments 1-11 1.3.1 The Physical State of the Interstellar Medium 1-11 1.3.2 Interstellar Clouds 1-15 1.3.3 HII Regions and Photodissociation Regions 1-17 1.3.4 The Interstellar Environment of the Solar System 1-19 1.4 Significance 1-22 1.4.1 From Cinderella to the Search for Origins 1-22 1.4.2 Dust in Astrochemistry 1-23 1.4.3 Dust as a Proxy for H 1-24 2 1.4.4 Dust as the Universal Thermal Regulator 1-25 1.4.5 Dust and Stellar Evolution 1-25 1.4.6 Starbursts and Luminous Infrared Galaxies 1-26 1.4.7 Back to Basics 1-27 References 1-28 2 The Interaction of Dust and Electromagnetic Radiation 2-1 2.1 Extinction 2-1 2.1.1 Extinction by Spherical Particles 2-1 2.1.2 Small-Particle Approximations 2-5 2.1.3 Albedo, Scattering Function, and Asymmetry Parameter 2-6 2.1.4 Absorption Features 2-7 2.1.5 Modeling Composite Grains 2-7 ix