We present phase-referenced VLBI observations of the radio continuum emission from , and the neutral hydrogen 21 cm absorption toward , the Luminous Infrared Galaxy NGC 7674 .
The observations were carried out at 1380 MHz using the Very Long Baseline Array , the phased Very Large Array , and the 305-m Arecibo radio telescope .
These observations constitute the first scientific use of the Arecibo telescope in a VLBI observation with the VLBA .
The high- and low-resolution radio continuum images reveal several new continuum structures in the nuclear region of this galaxy .
At \sim 100 mas resolution , we distinguish six continuum structures extending over 1.4 arcsec ( 742 pc ) , with a total flux density of 138 mJy .
Only three of these structures were known previously .
All these structures seem to be related to AGN activity .
The overall S-shaped pattern that the radio structures seem to form could be the result of the interstellar medium diverting the outcoming jets from the central AGN .
However , we can not rule out the possibility of a black hole merger that could result in a similar structural pattern .
At the full resolution of the array ( 11 \times 5 mas ) , we only detect two of the six continuum structures .
Both are composed of several compact components with brightness temperatures on the order of 10 ^ { 7 } K. While it is possible that one of these compact structures could host an AGN , they could also be shock-like features formed by the interaction of the jet with compact interstellar clouds in the nuclear region of this galaxy .
Complex H I absorption is detected with our VLBI array at both high and low angular resolution .
Assuming that the widest H I feature is associated with a rotating H I disk or torus feeding a central AGN , we estimate an enclosed dynamical mass of \sim 7 \times 10 ^ { 7 } ~ { } M { { } _ { \odot } } , comparable to the value derived from the hidden broad H \beta emission in this galaxy .
The narrower H I lines could represent clumpy neutral hydrogen structures in the H I torus .
The detection of H I absorption toward some of the continuum components , and its absence toward others , suggest an inclined H I disk or torus in the central region of NGC 7674 .
The overall averaged H I spectrum toward the continuum structures with H I absorption is very consistent with the Arecibo single dish H I absorption spectrum at 3 \hbox to 0.0 pt { . } ^ { \prime } 3 resolution .