The Parsec-Scale Radio Structure of NGC 1068 and the Nature of the Nuclear Radio Source

By J. Gallimore, S. Baum, C. O’Dea. 2004

145 citations recorded by the source corpus.

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 H2O 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 H2O 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 H2O 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.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/0047873a1c33f0dc8c07d4d138904647cf922987

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In Astronomy and Astrophysics

1. R. Genzel
2. P. Hopkins
3. H. Netzer
4. Roger Davies
5. L. Tacconi
6. L. Hernquist
7. A. Sternberg
8. A. Dekel

In Instrumentation

1. R. Genzel
2. L. Tacconi
3. Roger Davies
4. A. Sternberg
5. A. Eckart
6. Wolfgang J. Duschl
7. D. Asmus
8. E. Hicks

Citations in the corpus

• DUST IN THE POLAR REGION AS A MAJOR CONTRIBUTOR TO THE INFRARED EMISSION OF ACTIVE GALACTIC NUCLEI (2013, background): “The situation in NGC 3783 bears some resemblance to the changes of position angle on about the same scales seen in NGC 1068 (e.g. Gallimore et al. 2004).”
• A Close Look at Star Formation around Active Galactic Nuclei (2007, background): “This is clearly dominated by phenomena associated with the AGNs and jets, and our best estimate of the flux density away from these features is given by the lowest contour in maps such as Figure 1 of Gallimore et al. (2004).”
• OUTFLOWS FROM ACTIVE GALACTIC NUCLEI: KINEMATICS OF THE NARROW-LINE AND CORONAL-LINE REGIONS IN SEYFERT GALAXIES, (2011, background): “Mundell et al. (2003) and Gallimore et al. (2004) suggest that some NLR clouds in NGC 4151 and NGC 1068, respectively, are actually responsible for bending the radio jet.”
• Resolving the obscuring torus in NGC 1068 with the power of infrared interferometry: revealing the inner funnel of dust (2009, background): “Radio observations at 5 and 8.4GHz of the nucleus of NGC 1068 show a parsec-sized component (hereafter: ‘radio component’), most likely indicating free-free emission from the X-ray irradiated accretion disk (Gallimore et al. 2004).”
• Molecular line emission in NGC 1068 imaged with ALMA: I. An AGN-driven outflow in the dense molecular gas (2014, methodology): “This maximum coincides within the errors with the position of the AGN core (S 1) determined from VLBI radiocontinuum maps of the galaxy (Gallimore et al. 1996, 2004).”