WATER MASER EMISSION AND THE PARSEC-SCALE JET IN NGC-3079

We have conducted VLBI observations at subparsec resolution of water m aser and radio continuum emission in the nucleus of the nearby active galaxy NGC 3079. The 22 GHz maser emission arises in compact (similar to 0.01 pc at a distance of 16 Mpc) clumps, distributed over similar t o 2 pc along an axis that is approximately aligned with the major axis of the galactic disk. The Doppler velocities of the water maser clump s are consistent with their lying in the inner parsec of a molecular d isk with a binding mass similar to 10(6) M-circle dot, rotating in the same sense as the edge-on kiloparsec-scale molecular disk observed in CO emission. However, the velocity held has a significant nonrotation al component, which may indicate supersonic turbulence in the disk. Th is distribution is markedly different from that of water masers in NGC 4258, which trace a nearly perfectly Keplerian rotating disk with a b inding mass of 3.5 x 10(7) M-circle dot. The 22 GHz radio continuum em ission in NGC 3079 is dominated by a compact (<0.1 pc) source that is offset 0.5 pc to the west of the brightest maser feature. No bright ma ser emission is coincident with a detected compact continuum source. T his suggests that the large apparent luminosity of the maser is not ca used by beamed amplification of high brightness temperature continuum emission. At 8 and 5 GHz, we confirm the presence of two compact conti nuum sources with a projected separation of 1.5 pc. Both have inverted spectra between 5 and 8 GHz and steep spectra between 8 and 22 GHz. N GC 3079 may be a nearby, low-luminosity example of the class of compac t symmetric gigahertz-peaked spectrum radio sources. We detected a thi rd continuum component that lies along the same axis as the other two, strongly suggesting that this galaxy possesses a nuclear jet. Faint m aser emission was detected near this axis, which may indicate a second population of masers associated with the jet.