Deckers, M., Graur, O., Maguire, K., Shingles, L., Brennan, S.J., Anderson, J.P., Burke, J., Chen, T. -W., Galbany, L., Grayling, M.J.P., Gutiérrez, C.P., Harvey, L., Hiramatsu, D., Howell, D.A., Inserra, C., Killestein, T., McCully, C., Müller-Bravo, T.E., Nicholl, M., Newsome, M., Gonzalez, E. Padilla, Pellegrino, C., Terreran, G., Terwel, J.H., Toy, M. and Young, D.R. (2023) Photometric study of the late-time near-infrared plateau in Type Ia supernovae. Monthly Notices of the Royal Astronomical Society, 521 (3), 4414-4430. (doi:10.1093/mnras/stad841).
Abstract
We present an in-depth study of the late-time near-infrared plateau in Type Ia supernovae (SNe Ia), which occurs between 70 and 500 d. We double the existing sample of SNe Ia observed during the late-time near-infrared plateau with new observations taken with the Hubble Space Telescope, Gemini, New Technology Telescope, the 3.5-m Calar Alto Telescope, and the Nordic Optical Telescope. Our sample consists of 24 nearby SNe Ia at redshift < 0.025. We are able to confirm that no plateau exists in the Ks band for most normal SNe Ia. SNe Ia with broader optical light curves at peak tend to have a higher average brightness on the plateau in J and H, most likely due to a shallower decline in the preceding 100 d. SNe Ia that are more luminous at peak also show a steeper decline during the plateau phase in H. We compare our data to state-of-the-art radiative transfer models of nebular SNe Ia in the near-infrared. We find good agreement with the sub-Mch model that has reduced non-thermal ionization rates, but no physical justification for reducing these rates has yet been proposed. An analysis of the spectral evolution during the plateau demonstrates that the ratio of [Fe ii] to [Fe iii] contribution in a near-infrared filter determines the light curve evolution in said filter. We find that overluminous SNe decline slower during the plateau than expected from the trend seen for normal SNe Ia.
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