A dependence of the tidal disruption event rate on global stellar surface mass density and stellar velocity dispersion

Or Graur; K. Decker French; H. Jabran Zahid; James Guillochon; Kaisey S. Mandel; Katie Auchettl; Ann I. Zabludoff

doi:10.3847/1538-4357/aaa3fd

paper

A dependence of the tidal disruption event rate on global stellar surface mass density and stellar velocity dispersion

arXiv:1707.02986 · doi:10.3847/1538-4357/aaa3fd

Abstract

The rate of tidal disruption events (TDEs), $R_{TDE}$ , is predicted to depend on stellar conditions near the super-massive black hole (SMBH), which are on difficult-to-measure sub-parsec scales. We test whether $R_{TDE}$ depends on kpc-scale global galaxy properties, which are observable. We concentrate on stellar surface mass density, $Σ_{M_{⋆}}$ , and velocity dispersion, $σ_{v}$ , which correlate with the stellar density and velocity dispersion of the stars around the SMBH. We consider 35 TDE candidates, with and without known X-ray emission. The hosts range from star-forming to quiescent to quiescent with strong Balmer absorption lines. The last (often with post-starburst spectra) are overrepresented in our sample by a factor of $3 5_{- 17}^{+ 21}$ or $1 8_{- 7}^{+ 8}$ , depending on the strength of the H $δ$ absorption line. For a subsample of hosts with homogeneous measurements, $Σ_{M_{⋆}} = 1 0^{9}$ - $1 0^{10} M_{⊙} /kp c^{2}$ , higher on average than for a volume-weighted control sample of Sloan Digital Sky Survey galaxies with similar redshifts and stellar masses. This is because: (1) most of the TDE hosts here are quiescent galaxies, which tend to have higher $Σ_{M_{⋆}}$ than the star-forming galaxies that dominate the control, and (2) the star-forming hosts have higher average $Σ_{M_{⋆}}$ than the star-forming control. There is also a weak suggestion that TDE hosts have lower $σ_{v}$ than for the quiescent control. Assuming that $R_{TDE} \propto Σ_{M_{⋆}}^{α} \times σ_{v}^{β}$ , and applying a statistical model to the TDE hosts and control sample, we estimate $α^= 0.9 \pm 0.2$ and $β^= - 1.0 \pm 0.6$ . This is broadly consistent with $R_{TDE}$ being tied to the dynamical relaxation of stars surrounding the SMBH.

Accepted for publication in ApJ

A dependence of the tidal disruption event rate on global stellar surface mass density and stellar velocity dispersion

Abstract

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