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 three years (from October 2018 to September 2021). We infer the black hole (BH) mass ($M_{\mathrm{BH}}$) with host galaxy scaling relations, showing that the sample $M_{\mathrm{BH}}$ ranges from $10^{5.1}{M}_{\odot }$ to $10^{8.2}{M}_{\odot }$. We developed a survey efficiency corrected maximum volume method to infer the rates. The rest-frame $g$-band luminosity function (LF) can be well described by a broken power-law of $\ddot{I}•(L_g)\propto [(L_g/L_{\mathrm{bk}}{)}^{0.3}+(L_g/L_{\mathrm{bk}}{)}^{2.6}{]}^{-1}$, with $L_{\mathrm{bk}}=10^{43.1}\mathrm{erg}{\mathrm{s}}^{-1}$. In the BH mass regime of $10^{5.3}\lesssim (M_{\mathrm{BH}}/M_{\odot })\lesssim 10^{7.3}$, the TDE mass function follows $\ddot{I}•(M_{\mathrm{BH}})\propto M_{\mathrm{BH}}^{-0.25}$, which favors a flat local BH mass function ($d{n}_{\mathrm{BH}}/d\log M_{\mathrm{BH}}\approx \mathrm{constant}$). We confirm the significant rate suppression at the high-mass end ($M_{\mathrm{BH}}\gtrsim 10^{7.5}{M}_{\odot }$), which is consistent with theoretical predictions considering direct capture of hydrogen-burning stars by the event horizon. At a host galaxy mass of $M_{\mathrm{gal}}\sim 10^{10}{M}_{\odot }$, the average optical TDE rate is $\approx 3.2\times 10^{-5}\mathrm{galax}{\mathrm{y}}^{-1}\mathrm{y}{\mathrm{r}}^{-1}$. We constrain the optical TDE rate to be [3.7, 7.4, and 1.6$]\times 10^{-5}\mathrm{galax}{\mathrm{y}}^{-1}\mathrm{y}{\mathrm{r}}^{-1}$ in galaxies with red, green, and blue colors.

Replaced following peer-review process. 38 pages, 23 figures. Accepted for publication in ApJL