eROSITA-RU tidal disruption events with Keck-I/LRIS: Sample selection, optical properties, and host galaxy demographics

¹ Department of Astronomy, University of California, Berkeley, CA, 94720-3411, USA
² College of Physics, Sichuan University, Chengdu, 610065, China
³ Miller Institute for Basic Research in Science, 206B Stanley Hall, Berkeley, CA, 94720, USA
⁴ Berkeley Center for Multi-messenger Research on Astrophysical Transients and Outreach (Multi-RAPTOR), University of California, Berkeley, CA, 94720, USA
⁵ Space Research Institute (IKI), Russian Academy of Sciences, Profsoyuznaya 84/32, Moscow, 117997, Russia
⁶ Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, D-85741, Garching, Germany
⁷ Cahill Center for Astrophysics, California Institute of Technology, MC 249-17, 1200 E California Boulevard, Pasadena, CA, 91125, USA
⁸ Kazan Federal University, Kremlevskaya Str., 18, Kazan, 420008, Russia

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 15 December 2025
Accepted: 16 March 2026

Abstract

Context. We selected 70 tidal disruption event (TDE) candidates among X-ray transients discovered during the eROSITA all-sky surveys in the eastern Galactic hemisphere (0° < l < 180°) between December 2020 and February 2022 (eRASS1–5).

Aims. We performed a systematic analysis of this sample to characterize the properties of the optical counterparts and host galaxies of the TDE candidates.

Methods. We cross-matched each X-ray source to a host galaxy in archival optical surveys using Bayesian likelihood-ratio techniques and obtained Keck/LRIS spectroscopy for all 70 host galaxies. Host properties were inferred through a spectral energy distribution fitting with Prospector and emission line analysis with pPXF. We developed a robust classification scheme using X-ray and broad-line luminosities, narrow-line ionization diagnostics, and optical variability to identify high-confidence TDEs. For these, we analyzed optical spectral features, light curve properties, and host galaxy demographics.

Results. Our final sample contained 52 TDEs with redshifts of 0.018 ≤ z ≤ 0.714, comprising 41 gold (high-confidence) and 11 silver (lower-confidence) events. The majority (85%) of the gold TDEs are intrinsically brighter in the X-ray band, with L_X, peak > L_g, peak. Among the 23 gold TDEs with detected optical flares, delayed X-ray peaks are commonly observed. We identified transient spectral features in eight events, including six with prominent broad He IIλ4686 and/or Hα emission and two coronal-line TDEs. Host galaxy demographics revealed modest overrepresentation in green valley (×1.8) and quiescent Balmer-strong (×5.3) galaxies, which is significantly weaker than previous TDE samples, demonstrating greater diversity in star formation histories than previously recognized. Most TDE hosts exhibit suppressed star formation relative to the main sequence, consistent with X-ray selection biases against dusty star-forming galaxies.