Bibcode
Wevers, Thomas; Stone, Nicholas C.; van Velzen, Sjoert; Jonker, Peter G.; Hung, Tiara; Auchettl, Katie; Gezari, Suvi; Onori, Francesca; Mata Sánchez, Daniel; Kostrzewa-Rutkowska, Zuzanna; Casares, Jorge
Bibliographical reference
Monthly Notices of the Royal Astronomical Society, Volume 487, Issue 3, p.4136-4152
Advertised on:
8
2019
Citations
89
Refereed citations
82
Description
We present new medium resolution, optical long-slit spectra of a sample
of six ultraviolet (UV)/optical and 17 X-ray-selected tidal disruption
event candidate host galaxies. We measure emission line ratios from the
optical spectra, finding that the large majority of hosts are quiescent
galaxies, while those displaying emission lines are generally consistent
with star formation dominated environments; only three sources show
clear evidence of nuclear activity. We measure bulge velocity
dispersions using absorption lines and infer host black hole (BH) masses
using the M - σ relation. While the optical and X-ray host BH
masses are statistically consistent with coming from the same parent
distribution, the optical host distribution has a visible peak near M_BH
˜ 10^6 M_\odot, whereas the X-ray host distribution appears flat
in MBH. We find a subset of X-ray-selected candidates that
are hosted in galaxies significantly less luminous (Mg
˜ -16) and less massive (stellar mass ˜ 108.5-9
M⊙) than those of optical events. Using statistical tests
we find suggestive evidence that, in terms of BH mass, stellar mass, and
absolute magnitude, the hard X-ray hosts differ from the UV/optical and
soft X-ray samples. Similar to individual studies, we find that the size
of the emission region for the soft X-ray sample is much smaller than
the optical emission region, consistent with a compact accretion disc.
We find that the typical Eddington ratio of the soft X-ray emission is
˜ 0.01, as opposed to the optical events which have LBB
˜ LEdd. The latter seems artificial if the radiation is
produced by self-intersection shocks, and instead suggests a connection
to the supermassive black hole.
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