2005ApJ...622..178G

We present new very long baseline interferometry observations of the LINER galaxy NGC 4278. The observations were taken with the Very Long Baseline Array (VLBA) and a single antenna of the Very Large Array (VLA) at 5 and 8.4 GHz and have a linear resolution of ≲0.1 pc. Our radio data reveal a two-sided structure, with symmetric \ssf S-shaped jets emerging from a flat-spectrum core. We fit the jet brightness with Gaussian components, which we identify from a previous observation taken 5 years before. By comparing the positions of the components in the two epochs, we measure motions between 0.45±0.14 and 3.76±0.65 mas, corresponding to apparent velocities ≲0.2c and to ages in the range 8.3-65.8 yr. Assuming that the radio morphology is intrinsically symmetric and its appearance is governed by Doppler beaming effects, we find that NGC 4278 has mildly relativistic jets (β∼0.75), closely aligned to the line of sight (2°≤θ≤4°). Alternatively, the source could be oriented at a larger angle and asymmetries could be related to the jet interaction with the surrounding medium. We also present new simultaneous VLA observations between 1.4 and 43 GHz, and a 5 GHz light curve between 1972 and 2003. The radio spectrum can be fitted by a relatively steep power law (α=0.54). We find significant variability at 5 GHz. All these arguments indicate that the radiation from NGC 4278 is emitted via the synchrotron process by relativistic particles accelerated by a supermassive black hole. Despite a much lower power, this is the same process that takes place in ordinary radio-loud active galactic nuclei (AGNs).