TY - JOUR
T1 - A Theory for the Variation of Dust Attenuation Laws in Galaxies
AU - Narayanan, Desika
AU - Conroy, Charlie
AU - Davé, Romeel
AU - Johnson, Benjamin D.
AU - Popping, Gergö
N1 - Funding Information:
DN is grateful to Andrew Battisti, Daniela Calzetti, Ignacio Ferreras, Rob Kennicutt, Maciej Koprowski, Danielle Pierni, Karin Sandstrom, Samir Salim, Brett Salmon, James Trayford, Monica Tress, George Privon, and Adolf Witt for valuable conversations during this study. We additionally thank Mariska Kriek, Samir Salim, and Brett Salmon for providing data to us for our comparisons with observations. After posting to the arXiv, George Privon, Samir Salim, and Mike Shull individually alerted us to typographical errors, which we are grateful for. The simulations published here were run on the University of Florida HiPerGator supercomputing facility, and the authors acknowledge the University of Florida Research Computing for providing computational resources and support that have contributed to the research results reported in this publication. This study was funded in part by NSF AST-1715206 and HST AR-15043.0001.
Publisher Copyright:
© 2018. The American Astronomical Society. All rights reserved.
PY - 2018/12/10
Y1 - 2018/12/10
N2 - In this paper, we provide a physical model for the origin of variations in the shapes and bump strengths of dust attenuation laws in galaxies by combining a large suite of cosmological "zoom-in" galaxy formation simulations with 3D Monte Carlo dust radiative transfer calculations. We model galaxies over three orders of magnitude in stellar mass, ranging from Milky Way-like systems to massive galaxies at high redshift. Critically, for these calculations, we employ a constant underlying dust extinction law in all cases and examine how the role of geometry and radiative transfer effects impacts the resultant attenuation curves. Our main results follow. Despite our usage of a constant dust extinction curve, we find dramatic variations in the derived attenuation laws. The slopes of normalized attenuation laws depend primarily on the complexities of star-to-dust geometry. Increasing fractions of unobscured young stars flatten normalized curves, while increasing fractions of unobscured old stars steepen curves. Similar to the slopes of our model attenuation laws, we find dramatic variation in the 2175 ultraviolet bump strength, including a subset of curves with little to no bump. These bump strengths are primarily influenced by the fraction of unobscured O and B stars in our model, with the impact of scattered light having only a secondary effect. Taken together, these results lead to a natural relationship between the attenuation curve slope and 2175 bump strength. Finally, we apply these results to a 25 Mpc h -1 box cosmological hydrodynamic simulation in order to model the expected dispersion in attenuation laws at integer redshifts from z = 0 to 6. A significant dispersion is expected at low redshifts and decreases toward z = 6. We provide tabulated results for the best-fit median attenuation curve at all redshifts.
AB - In this paper, we provide a physical model for the origin of variations in the shapes and bump strengths of dust attenuation laws in galaxies by combining a large suite of cosmological "zoom-in" galaxy formation simulations with 3D Monte Carlo dust radiative transfer calculations. We model galaxies over three orders of magnitude in stellar mass, ranging from Milky Way-like systems to massive galaxies at high redshift. Critically, for these calculations, we employ a constant underlying dust extinction law in all cases and examine how the role of geometry and radiative transfer effects impacts the resultant attenuation curves. Our main results follow. Despite our usage of a constant dust extinction curve, we find dramatic variations in the derived attenuation laws. The slopes of normalized attenuation laws depend primarily on the complexities of star-to-dust geometry. Increasing fractions of unobscured young stars flatten normalized curves, while increasing fractions of unobscured old stars steepen curves. Similar to the slopes of our model attenuation laws, we find dramatic variation in the 2175 ultraviolet bump strength, including a subset of curves with little to no bump. These bump strengths are primarily influenced by the fraction of unobscured O and B stars in our model, with the impact of scattered light having only a secondary effect. Taken together, these results lead to a natural relationship between the attenuation curve slope and 2175 bump strength. Finally, we apply these results to a 25 Mpc h -1 box cosmological hydrodynamic simulation in order to model the expected dispersion in attenuation laws at integer redshifts from z = 0 to 6. A significant dispersion is expected at low redshifts and decreases toward z = 6. We provide tabulated results for the best-fit median attenuation curve at all redshifts.
KW - dust extinction
KW - galaxies: ISM
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U2 - 10.3847/1538-4357/aaed25
DO - 10.3847/1538-4357/aaed25
M3 - Article
AN - SCOPUS:85058496342
VL - 869
JO - Astrophysical Journal
JF - Astrophysical Journal
SN - 0004-637X
IS - 1
M1 - 70
ER -