Tidal Disruption Event Demographics with the Zwicky Transient Facility: Volumetric Rates, Luminosity Function, and Implications for the Local Black Hole Mass Function

Abstract

We conduct a systematic tidal disruption event (TDE) demographics analysis using the largest sample of optically selected TDEs. A flux-limited, spectroscopically complete sample of 33 TDEs is constructed using the Zwicky Transient Facility over 3 yr (from 2018 October to 2021 September). We infer the black hole (BH) mass (M ${}_{B}H$) with host galaxy scaling relations, showing that the sample M ${}_{B}H$ ranges from 10${}^5.1$ M ${}_{ø}dot$ to 10${}^8.2$ M ${}_{ø}dot$. We developed a survey efficiency corrected maximum volume method to infer the rates. The rest- frame g-band luminosity function can be well described by a broken power law of $\varphi (L_g)\propto łeft[łeft(L_g/L_{m}athrmbki̊ght{)}^0.3+łeft(L_g/L_{m}athrmbkg̊ht{)}^2.6rh̊t{]}^{-}1$ , with L ${}_{b}k$ = 10${}^{4}3.1$ erg s${}^{-}1$. In the BH mass regime of 10${}^5.3$ łesssim (M ${}_{B}H$/M ${}_{ø}dot$) łesssim 10${}^7.3$, the TDE mass function follows $\varphi (M_{m}athrmBH)\propto M_{m}athrmB{H}^{-}0.25$ , which favors a flat local BH mass function ( $d{n}_{m}athrmBH/dmathrmlog{M}_{m}athrmBH\approx mathrmconstant$ ). We confirm the significant rate suppression at the high-mass end (M ${}_{B}H$ gtrsim 10${}^7.5$ M ${}_{ø}dot$), which is consistent with theoretical predictions considering direct capture of hydrogen-burning stars by the event horizon. At a host galaxy mass of M ${}_{g}al$ rae̊box-0.5ex 10${}^{1}0$ M ${}_{ø}dot$, the average optical TDE rate is ≈3.2 × 10${}^{-}5$ galaxy${}^{-}1$ yr${}^{-}1$. We constrain the optical TDE rate to be [3.7, 7.4, and 1.6] × 10${}^{-}5$ galaxy${}^{-}1$ yr${}^{-}1$ in galaxies with red, green, and blue colors.