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Photometric study of the late-time near-infrared plateau in Type Ia supernovae

M. DeckersO. GraurK. Maguire ...+22 D. R. Young
Mar 2023
We present an in-depth study of the late-time near-infrared plateau in TypeIa supernovae (SNe Ia), which occurs between 70-500 d. We double the existingsample of SNe Ia observed during the late-time near-infrared plateau with newobservations taken with the Hubble Space Telescope, Gemini, New TechnologyTelescope, the 3.5m Calar Alto Telescope, and the Nordic Optical Telescope. Oursample consists of 24 nearby SNe Ia at redshift < 0.025. We are able to confirmthat no plateau exists in the Ks band for most normal SNe Ia. SNe Ia withbroader optical light curves at peak tend to have a higher average brightnesson the plateau in J and H, most likely due to a shallower decline in thepreceding 100 d. SNe Ia that are more luminous at peak also show a steeperdecline during the plateau phase in H. We compare our data to state-of-the-artradiative transfer models of nebular SNe Ia in the near-infrared. We find goodagreement with the sub-Mch model that has reduced non-thermal ionisation rates,but no physical justification for reducing these rates has yet been proposed.An analysis of the spectral evolution during the plateau demonstrates that theratio of [Fe II] to [Fe III] contribution in a near-infrared filter determinesthe light curve evolution in said filter. We find that overluminous SNe declineslower during the plateau than expected from the trend seen for normal SNe Ia