dc.contributor.author | Gallimore, Jack | en_US |
dc.contributor.author | Baum, Stefi | en_US |
dc.contributor.author | O'Dea, Christopher | en_US |
dc.date.accessioned | 2006-05-04T17:58:47Z | en_US |
dc.date.available | 2006-05-04T17:58:47Z | en_US |
dc.date.issued | 2004-10-01 | en_US |
dc.identifier.citation | Astrophys.J. 613 (2004) 794-810 | en_US |
dc.identifier.issn | 1538-4365 | en_US |
dc.identifier.uri | http://hdl.handle.net/1850/1746 | en_US |
dc.description | RIT community members may access full-text via RIT Libraries licensed databases: http://library.rit.edu/databases/ | |
dc.description.abstract | We present sensitive, multifrequency Very Long Baseline Array (VLBA2) images of the nuclear
radio sources of NGC 1068. At 5 GHz 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 freefree
absorption below 5 GHz, and it has a flat spectrum between 5 GHz 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 which 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 denser jet plasma that broke
away from an earlier interaction with the circumnuclear ISM. | en_US |
dc.description.sponsorship | JFG was supported by a Jansky fellowship at NRAO-Charlottesville during the formative
work on this project. JFG received further support from a DDRF grant for research leave
at STScI. Ali Kinkhabwala kindly provided an electronic version of the XMM-Newton
RGB spectrum. This work greatly benefited from conversations with Moshe Elitzur,
Hagai Netzer, Martin Elvis, & Julian Krolik. We also thank an anonymous referee who
pointed out some technical errors and made helpful suggestions that improved the error
analysis. | en_US |
dc.format.extent | 574675 bytes | en_US |
dc.format.mimetype | application/pdf | en_US |
dc.language.iso | en_US | en_US |
dc.publisher | American Astronomical Society | en_US |
dc.relation.ispartofseries | vol. 613 | en_US |
dc.relation.ispartofseries | no. 2 | en_US |
dc.subject | Galaxies - active | en_US |
dc.subject | Galaxies - individual - NGC 1068 | en_US |
dc.subject | Galaxies - nuclei | en_US |
dc.subject | Galaxies - Seyfert | en_US |
dc.title | The Parsec-scale radio structure of NGC 1068 and the nature of the nuclear radio source | en_US |
dc.type | Article | en_US |
dc.identifier.url | http://dx.doi.org/10.1086/423167 | |