We present sensitive, multifrequency Very Long Baseline Array (VLBA) images of the nuclear radio sources of NGC 1068. At 5 and 8.4 GHz, the radio continuum source S1, argued to mark the location of the hidden active nucleus, resolves into an elongated, $0.8 pc source oriented nearly at right angles to the radio jet axis but more closely aligned to the distribution of the nuclear H 2 O maser spots. S1 is detected at 5 GHz but not at 1.4 GHz, indicating strong free-free absorption below 5 GHz, and it has a flat spectrum between 5 and 8.4 GHz. A 5-8.4 GHz spectral index map reveals an unresolved, inverted spectrum source at the center of the S1 structure that may mark the AGN proper. The average brightness temperature is too low for synchrotron self-absorption to impact the integrated spectrum significantly. In addition, a careful registration with the nuclear H 2 O masers argues that the S1 continuum source arises from the inner regions of the maser disk rather than a radio jet. The emission mechanism may be direct, thermal free-free emission from an X-ray-heated corona or wind arising from the molecular disk. We demonstrate that the hidden active nucleus is sufficiently luminous, to within the current estimates, to provide the requisite heating. The radio jet components C and S2 both show evidence for free-free absorption of a compact, steep-spectrum source. The free-free absorption might arise from a shock cocoon enveloping the compact radio sources. The presence of H 2 O masers specifically at component C supports the interpretation for the presence of a jet-ISM interaction. Component NE remains a steep-spectrum source on VLBA baselines and appears to be a local enhancement of the synchrotron emissivity of the radio jet. The reason for the enhancement is not clear; the region surrounding component NE is virtually devoid of narrow-line region filaments, and so there is no clear evidence for interaction with the surrounding ISM. Component NE might instead arise in an internal shock or perhaps in denser jet plasma that broke away from an earlier interaction with the circumnuclear ISM.

We report resolution, interferometric observations of the 1.3 mm CO J \ 2 ] 1 line in the 0A .5 ] 0A .9 infrared luminous galactic merger NGC 6240. About half of the CO Ñux is concentrated in a rotating but highly turbulent, thick disk structure centered between the two radio and near-infrared nuclei. A number of gas features connect this D500 pc diameter central disk to larger scales. Throughout this region the molecular gas has local velocity widths which exceed 300 km s~1 FWHM and even reach FWZP line widths of 1000 km s~1 in a number of directions. The mass of the central gas concentration constitutes a signiÐcant fraction of the dynamical mass, pc) D(2È4) ] 109 M gas (R ¹ 470 M _ D We conclude that NGC 6240 is in an earlier merging stage than the prototypical ultralu-(0.3È0.7)M dyn . minous galaxy, Arp 220. The interstellar gas in NGC 6240 is in the process of settling between the two progenitor stellar nuclei, is dissipating rapidly, and will likely form a central thin disk. In the next merger stage, NGC 6240 may well experience a major starburst like that observed in Arp 220.

Seyfert galaxies commonly host compact jets spanning 10-100 pc scales, but larger structures are resolved out in long-baseline aperture synthesis surveys. Previous, targeted studies showed that kiloparsec-scale radio structures ( KSRs) may be a common feature of Seyfert and LINER galaxies, and the origin of KSRs may be starbursts or active galactic nuclei (AGNs). We report a new Very Large Array survey of a complete sample of Seyfert and LINER galaxies. Out of all of the surveyed radio-quiet sources, we find that 44% (19 out of 43) show extended radio structures at least 1 kpc in total extent that do not match the morphology of the disk or its associated star-forming regions. The detection rate is a lower limit owing to the combined effects of projection and resolution. The infrared colors of the KSR host galaxies are unremarkable compared to other Seyfert galaxies, and the large-scale outflows orient randomly with respect to the host galaxy axes. The KSR Seyfert galaxies instead stand out by deviating significantly from the far-infrared-radio correlation for star-forming galaxies, with tendency toward radio excess, and they are more likely to have a relatively luminous, compact radio source in the nucleus; these results argue that KSRs are powered by the AGNs rather than starbursts. The high detection rate indicates that Seyfert galaxies generate radio outflows over a significant fraction of their lifetime, which is much longer than the dynamical timescale of an AGNpowered jet but is comparable instead to the buoyancy timescale. The likely explanation is that the KSRs originate from jet plasma that has been decelerated by interaction with the nuclear interstellar medium ( ISM ). Based on a simple ram pressure argument, the kinetic power of the jet on kiloparsec scales is about 3 orders of magnitude weaker than the power of the jet on 10-100 pc scales. This result is consistent with the interaction model, in which case virtually all of the jet power must be lost to the ISM within the inner kiloparsec.

The VLA has been used at 3.6 and 20 cm to image a sample of about 50 early-type Seyfert galaxies with recessional velocities less than 7,000 km s −1 and total visual magnitude less than 14.5. Emission-line ([OIII] and Hα+[NII]) and continuum (green and red) imaging of this sample has been presented in a previous paper. In this paper, we present the radio results, discuss statistical relationships between the radio and other properties and investigate these relationships within the context of unified models of Seyferts. The mean radio luminosities of early-type Seyfert 1's (i.e. Seyfert 1.0's, 1.2's and 1.5's) and Seyfert 2.0's are found to be similar (consistent with the unified scheme) and the radio luminosity is independent of morphological type within this sample. The fraction of resolved radio sources is larger in the Seyfert 2.0's (93%) than in the Seyfert 1's (64%). However, the mean radio extents of Seyfert 2.0's and Seyfert 1's are not significantly different, though this result is limited by the small number of resolved Seyfert 1's.The nuclear radio structures of Seyfert 2.0's in the early-type sample tend to be aligned with the [OIII] and Hα+[NII] structures even though the radio extents are smaller than the [OIII] and Hα+[NII] extents by a factor of ∼ 2 ->5. This alignment, previously known for individual Seyferts with 'linear' radio sources, is here shown to be characteristic of early-type Seyfert galaxies as a -2class. Seyfert 2.0's in the early-type sample also show a significant alignment between the emission-line ([OIII] and Hα+[NII]) axes and the major axis of the host galaxy. These alignments are consistent with a picture in which the ionized gas represents ambient gas predominantly co-planar with the galaxy stellar disk. This ambient gas is ionized by nuclear radiation that may escape preferentially along and around the radio axis, and is compressed in shocks driven by the radio ejecta. We use this alignment to constrain the product of the velocity of the radio ejecta and the period of any large angle precession of the inner accretion disk and jet : V ejecta × P ≥ 2 kpc.An investigation of a larger sample of Seyferts reveals the unexpected result that the Seyfert 1's with the largest radio extent (≥ 1.5 kpc) are all of type Seyfert 1.2. It appears that classification as this type of intermediate Seyfert depends on some factor other than the relative orientation of the nuclear obscuring torus to the line of sight. Among all the other Seyferts, the distribution of radio extent with Seyfert intermediate type is consistent with the expectations of the unified scheme.