High-frequency excess in the radio continuum spectrum of the type-1
  Seyfert galaxy NGC 985
  The Seyfert galaxy NGC 985 is known to show a high-frequency excess in its
radio continuum spectrum in a milli-Jansky level on the basis of previous
observations at 1.4--15 GHz; a steep spectrum at low frequencies (a spectral
index of $\alpha=-1.10 \pm 0.03$) changes at ~10 GHz into an inverted spectrum
at higher frequencies ($\alpha=+0.86 \pm 0.09$). We conduct new observations at
15--43 GHz using the Very Large Array and at 100 GHz using the Nobeyama
Millimeter Array. As a result, the high-frequency excess continuing at even
higher radio frequencies up to 43 GHz has been confirmed. The non-detection at
100 GHz was not so strong constraint, and therefore the spectral behavior above
43 GHz remains unclear. The astrometric position of the high-frequency excess
component coincides with the optical position of the Seyfert nucleus and the
low-frequency radio position to an accuracy of 0.1 arcsec, corresponding to ~80
pc; the radio source size is constrained to be <0.02 arcsec, corresponding to
<16 pc. We discuss the physical origin of the observed high-frequency excess
component. Dust emission at the Rayleigh-Jeans regime, free--free emission from
X-ray radiating high-temperature plasma, free--free emission from the ensemble
of broad-line region clouds, or thermal synchrotron from hot accretion flow
cannot be responsible for the observed radio flux. Compact jets under
synchrotron self-absorption may be unlikely in terms of observed time scales.
Alternatively, we cannot rule out the hypotheses of synchrotron jets free--free
absorbed by a circumnuclear photo-ionized region, and self-absorbed nonthermal
synchrotron from disk corona, as the origin of the high-frequency excess
component.
