Dust Extinction toward Type Ia Supernovae

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Type Ia supernovae (SNe Ia) are powerful cosmological "standardizable candles" and the most precise indicators of the distance to faraway galaxies. This makes them critical for measuring the expansion rate of the universe. However, a limiting factor in their use for precision cosmology rests on our ability to correct for the dimming of SNe light due to intervening dust, a phenomenon known as "dust extinction." Astronomers at the University of Missouri - Columbia will study the dust extinction toward SNe Ia through a systematic exploration of about 60 SNe Ia observed by space-borne and ground-based telescopes over a broad wavelength range spanning from the ultraviolet through the optical to the near infrared. By comparing the observed photometry (spectrum and intensity of light) of each SN Ia with that of a pristine template SN Ia without extinction, the researchers will determine the extinction quantity and its wavelength dependence (i.e., extinction curve). The derived extinction curve will be compared to theoretical models, enabling the scientists to explore the dust size and composition for each SN Ia. Finally, the researchers will explore whether and how the dust and extinction properties vary systematically with the intrinsic properties of SNe Ia as well as with relevant properties of their host galaxies. This research will have a positive impact on training graduate students and on developing an undergraduate astronomy program at the University of Missouri, as well as educating non-science majors and the general public, through a vigorous program of community outreach.A longstanding puzzle in the analysis of SN Ia light curves is the nature of their apparent color and brightness variations. The "redder-dimmer'' color-luminosity relation widely used in cosmological SN Ia analyses masks the fact that it has two separate physical origins: (i) an intrinsic correlation, which arises from the physics of exploding white dwarfs and (ii) an apparent dimming and reddening due to interstellar dust in the host galaxy. The researchers will explore whether and how the dust and extinction properties vary systematically with the intrinsic properties of SNe Ia (e.g., intrinsic color, luminosity, light-curve shape, decline rate, spectroscopic properties, and expansion velocity) as well as the properties of their host galaxies (e.g., morphological type, metallicity). The work will help astronomers to understand the dominant systematic effects for the determination of cosmological parameters from SNe Ia, knowledge of SNe intrinsic colors and dimming due to extinction by host galaxy. It could thus impact both supernova cosmology and the knowledge of extragalactic extinction.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.