Tidal Disruption Event Hosts Are Green and Centrally Concentrated: Signatures of a Post-merger System

Hammerstein, Erica; Gezari, Suvi; Velzen, S. van; Cenko, S. Bradley; Roth, Nathaniel; Ward, Charlotte; Frederick, Sara; Hung, T.; Graham, M. J.; Foley, R. J.; Bellm, Eric C.; Cannella, Christopher; Drake, A. J.; Kupfer, Thomas; Laher, Russ R.; Mahabal, A.; Masci, Frank J.; Riddle, Reed; Rojas-Bravo, C.; Smith, Roger M.

doi:10.3847/2041-8213/abdcb4

Cited by 42 publications

(54 citation statements)

References 40 publications

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“…About 15% of these are spectroscopically confirmed SN. The photometric selection recovers all ZTF TDEs and all large-amplitude flares from Seyfert galaxies that have been reported in earlier work (12,23,42).…”

Section: A Flare Selection and Photometrysupporting

confidence: 66%

Establishing accretion flares from massive black holes as a major source of high-energy neutrinos

Velzen¹,

Stein²,

Gilfanov³

et al. 2021

Preprint

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High-energy neutrinos have thus far been observed in coincidence with timevariable emission from three different accreting black holes: a gamma-ray flare from a blazar (TXS 0506+056), an optical transient following a stellar tidal disruption (AT2019dsg), and an optical outburst from an active galactic nucleus (AT2019fdr). Here we present a unified explanation for the latter two of these sources: accretion flares that reach the Eddington limit. A signature of these events is a luminous infrared reverberation signal from circumnuclear dust that is heated by the flare. Using this property we construct a sample of similar sources, revealing a third event coincident with a PeV-scale neutrino. This sample of three accretion flares is correlated with high-energy neutrinos at a significance of 3.7σ. Super-Eddington accretion could explain the high particle acceleration efficiency of this new population.Accreting black holes have long been suggested as potential sources of high-energy particles (1, 2) and this expectation was supported by the detection of a high-energy neutrino coincident (at the 3σ-level) with gamma-ray flaring from the blazar TXS 0506+056 (3). However, blazars alone cannot account for the observed high-energy neutrino flux (4, 5); similar to the electromagnetic sky, we can expect that the observed cosmic neutrino flux (6) arises from multiple source populations (7).In the last two years, optical follow-up observations of neutrino alerts (8) using the Zwicky Transient Facility (ZTF, ( 9)) have identified two optical flares from the centers of galaxies coincident with PeV-scale neutrinos: AT2019dsg (10) and AT2019fdr (11). The former belongs to the class of spectroscopically-classified tidal disruption events (TDEs) from quiescent black holes, while the latter originated from a type 1 (i.e., unobscured) active galactic nucleus (AGN).However, the distinctive shared properties we present below suggest these flares share a common origin.

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Section: A Flare Selection and Photometrysupporting

confidence: 66%

Establishing accretion flares from massive black holes as a major source of high-energy neutrinos

Velzen¹,

Stein²,

Gilfanov³

et al. 2021

Preprint

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“…The extinction is roughly consistent with the Galactic foreground extinction of E(B − V) = 0.06 (Schlafly & Finkbeiner 2011). The estimated mass combined with the extinction-corrected rest-frame colour u − r = 1.89 ± 0.02 mag places the host galaxy near the "green valley" region (Schawinski et al 2014) of the mass colour diagram, in which the TDE host galaxies seems to be over represented compared to the general galaxy population (Law- Smith et al 2017;Hammerstein et al 2021).…”

Section: Spectral Energy Distributionsupporting

confidence: 70%

An elliptical accretion disk following the tidal disruption event AT 2020zso

Wevers,

Nicholl,

Guolo

et al. 2022

Preprint

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Aims. Modeling spectroscopic observations of tidal disruption events (TDEs) to date suggests that the newly-formed accretion disks are mostly quasi-circular. In this work we study the transient event AT 2020zso, hosted by an active galactic nucleus (AGN; as inferred from narrow emission line diagnostics), with the aim of characterising the properties of its newly formed accretion flow. Methods. We classify AT 2020zso as a TDE based on the blackbody evolution inferred from UV/optical photometric observations, and spectral line content and evolution. We identify transient, double-peaked Bowen (N iii), He i, He ii and Hα emission lines. We model medium resolution optical spectroscopy of the He ii (after careful deblending of the N iii contribution) and Hα lines during the rise, peak and early decline of the light curve using relativistic, elliptical accretion disk models. Results. We find that the spectral evolution before peak can be explained by optical depth effects consistent with an outflowing, optically thick Eddington envelope. Around peak the envelope reaches its maximum extent (approximately 10 15 cm, or ∼ 3000 -6000 gravitational radii for an inferred black hole mass of 5 − 10 × 10 5 M ) and becomes optically thin. The Hα and He ii emission lines at and after peak can be reproduced with a highly inclined (i = 85 ± 5 degrees), highly elliptical (e = 0.97 ± 0.01) and relatively compact (R in = several 100 R g and R out = several 1000 R g ) accretion disk. Conclusions. Overall, the line profiles suggest a highly elliptical geometry for the new accretion flow, consistent with theoretical expectations of newly formed TDE disks. We quantitatively confirm, for the first time, the high inclination nature of a Bowen (and X-ray dim) TDE, consistent with the unification picture of TDEs where the inclination largely determines the observational appearance. Rapid line profile variations rule out the binary SMBH hypothesis as the origin of the eccentricity; these results thus provide a direct link between a TDE in an AGN and the eccentric accretion disk. We illustrate for the first time how optical spectroscopy can be used to constrain the black hole spin, through (the lack of) disk precession signatures (changes in inferred inclination). We constrain the disk alignment timescale to > 15 days in AT2020zso, which rules out high black hole spin values (a < 0.8) for M BH ∼ 10 6 M and disk viscosity α 0.1.

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“…The overrepresentation of TDEs in poststarbursts was initially estimated to be as large as a factor ∼ 100 for E+A and ∼ 30 for quiescent Balmer strong hosts (French et al 2016;Graur et al 2018). Law-Smith et al (2017) showed that, once accounting for selection effects, the E+A poststarburst preference should be reduced by a factor ≈ 4, bringing the overall poststarburst preference to nearly 15 − 30, as later confirmed by Hammerstein et al (2021).…”

Section: Introductionmentioning

confidence: 89%

“…The opening of this golden era for TDEs has come with its own surprises. Together with the accumulation of the first dozens of detections, population studies of TDE hosts have revealed that these events are significantly overrepresented in poststarburst galaxies (Arcavi et al 2014;French et al 2016French et al , 2017Law-Smith et al 2017;Graur et al 2018;French et al 2020;Hammerstein et al 2021). The spectra of these galaxies lack strong emission lines, suggesting low current star formation rates, but feature strong Balmer absorption lines, a signature that reveals the presence of many young stars, and it is associated with a starburst over the last ≈1 Gyr (see e.g.…”

Section: Introductionmentioning

confidence: 99%

Tidal disruption events in post-starburst galaxies: the importance of a complete stellar mass function

Bortolas

2022

Preprint

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A tidal disruption event (TDE) occurs when a star is destroyed by the strong tidal shear of a massive black hole (MBH). The accumulation of TDE observations over the last years has revealed that poststarburst galaxies are significantly overrepresented in the sample of TDE hosts. Here we address the poststarburst preference by investigating the decline of TDE rates in a Milky-Way like nuclear stellar cluster featuring either a monochromatic (1 M ) or a complete, evolved stellar mass function. In the former case, the decline of TDE rates with time is very mild, and generally up to a factor of a few in 10 Gyr. Conversely, if a complete mass function is considered, a strong TDE burst over the first 0.1 − 1 Gyr is followed by a considerable rate drop, by at least an order of magnitude over 10 Gyr. The decline starts after a mass segregation timescale, and it is more pronounced assuming a more top-heavy initial mass function and/or an initially denser nucleus. Our results thus suggest that the poststarburst preference can be accounted for in realistic systems featuring a complete stellar mass function, even in moderately dense galactic nuclei. Overall, our findings support the idea that starbursting galactic nuclei are characterized by a top-heavy initial mass function; we speculate that accounting for this can reconcile the discrepancy between observed and theoretically predicted TDE rates even in quiescent galaxies.

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Tidal Disruption Event Hosts Are Green and Centrally Concentrated: Signatures of a Post-merger System

Cited by 42 publications

References 40 publications

Establishing accretion flares from massive black holes as a major source of high-energy neutrinos

Establishing accretion flares from massive black holes as a major source of high-energy neutrinos

An elliptical accretion disk following the tidal disruption event AT 2020zso

Tidal disruption events in post-starburst galaxies: the importance of a complete stellar mass function

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