Low-luminosity Type IIP Supernovae from the Zwicky Transient Facility Census of the Local Universe. I. Luminosity Function, Volumetric Rate

We present the luminosity function and volumetric rate of a sample of Type IIP supernovae (SNe) from the Zwicky Transient Facility Census of the Local Universe survey (CLU). This is the largest sample of Type IIP SNe from a systematic volume-limited survey to-date. The final sample includes 330 Type IIP SNe and 36 low-luminosity Type II (LLIIP) SNe with M_r,peak > −16 mag, which triples the literature sample of LLIIP SNe. The fraction of LLIIP SNe is 19_-⁺₄³% of the total CLU Type IIP SNe population (8_-⁺₂¹% of all core-collapse SNe). This implies that while LLIIP SNe likely represent the fate of core-collapse SNe of 8-12 M_e progenitors, they alone cannot account for the fate of all massive stars in this mass range. To derive an absolute rate, we estimate the ZTF pipeline efficiency as a function of the apparent magnitude and the local surface brightness. We derive a volumetric rate of (3.9_-⁺_0.4^0.4) ´ 10⁴ Gpc^-3 yr^-1 for Type IIP SNe and (7.3_-⁺_0.6^0.6) ´ 10³ Gpc^-3 yr^-1 for LLIIP SNe. Now that the rate of LLIIP SNe is robustly derived, the unresolved discrepancy between core-collapse SN rates and star formation rates cannot be explained by LLIIP SNe alone.