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


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 $_BH$) with host galaxy scaling relations, showing that the sample M $_BH$ ranges from 10$^5.1$ M $_ødot$ to 10$^8.2$ M $_ødot$. 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 $ϕ (L_g)∝ łeft[łeft(L_g /L_mathrmbki̊ght)^0.3+łeft(L_g/L_mathrmbk g̊ht)^2.6rh̊t]^-1$ , with L $_bk$ = 10$^43.1$ erg s$^-1$. In the BH mass regime of 10$^5.3$ łesssim (M $_BH$/M $_ødot$) łesssim 10$^7.3$, the TDE mass function follows $ϕ (M_mathrmBH)∝ M_mathrmBH^-0.25$ , which favors a flat local BH mass function ( $dn_mathrmBH/dmathrmlogM_mathrmBH≈ mathrmconstant$ ). We confirm the significant rate suppression at the high-mass end (M $_BH$ gtrsim 10$^7.5$ M $_ødot$), which is consistent with theoretical predictions considering direct capture of hydrogen-burning stars by the event horizon. At a host galaxy mass of M $_gal$ rae̊box-0.5ex 10$^10$ M $_ødot$, 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.

Astrophysical Journal Letters