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 \sim 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 \sim 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 can not be responsible for the observed radio flux .
Compact jets under synchrotron self-absorption may be unlikely in terms of observed time scales .
Alternatively , we can not 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 .