The Subarcsecond Radio Structure in NGC 1068. I. Observations and Results

Gallimore, J. F.; Baum, S. A.; O’Dea, C. P.; Pedlar, A.

doi:10.1086/176798

Cited by 145 publications

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“…The circles represent the beam sizes at 130.3 GHz (19 ) and 86.8 GHz (28 ). the position of the active nucleus identified as the compact radio-source S1 in the map of Gallimore et al (1996a). Most remarkably, the CND is prominent in HCN emission .…”

Section: Introductionmentioning

confidence: 88%

Molecular gas chemistry in AGN

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García‐Burillo

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et al. 2004

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Abstract. There is observational evidence that nuclear winds and X-rays can heavily influence the physical conditions and chemical abundances of molecular gas in the circumnuclear disks (CND) of Active Galactic Nuclei (AGN). In this paper we probe the chemical status of molecular gas in the CND of NGC 1068, a prototypical Seyfert 2 galaxy. Precedent claims that the chemistry of molecular gas in the nucleus of NGC 1068 is abnormal by galactic standards were based on the high HCN/CO luminosity ratio measured in the CND. Results from new observations obtained in this survey have served to derive abundances of molecular species such as SiO, CN, HCO + , HOC + , H 13 CO + and HCO. These estimates are complemented by a re-evaluation of molecular abundances for HCN, CS and CO, based on previously published single-dish and interferometer observations of NGC 1068. We report on the first detection of SiO emission in the CND of NGC 1068. The estimated large abundance of SiO in the CND, X(SiO) ∼ (5−10) × 10 −9 , cannot be attributed to shocks related to star formation, as there is little evidence of a recent starburst in the nucleus of NGC 1068. Alternatively, we propose that silicon chemistry is driven by intense X-ray processing of molecular gas. We also report on the first extragalactic detection of the reactive ion HOC + . Most remarkably, the estimated HCO + /HOC + abundance ratio in the nucleus of NGC 1068, ∼30-80, is the smallest ever measured in molecular gas. The abundances derived for all molecules that have been the subject of this survey are compared with the predictions of models invoking either oxygen-depletion or X-ray chemistry in molecular gas. Our conclusions favour an overall scenario where the CND of NGC 1068 has become a giant X-ray Dominated Region (XDR).

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Section: Introductionmentioning

confidence: 88%

Molecular gas chemistry in AGN

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García‐Burillo

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et al. 2004

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“…This choice allowed us to cover the SiO line at 3 mm and the CN lines at 1 mm. Gallimore et al 1996). Visibilities were obtained through on-source integration times of 20 min framed by short (∼2 min) phase and amplitude calibrations on the nearby quasars 0235+164 and 0336-019.…”

Section: Interferometric Mapsmentioning

confidence: 99%

“…Other scenarios designed to fit the CND kinematics, in particular those invoking a jet-ISM interaction, which would give rise to a nuclear warp and, eventually, to an expanding ring, could produce faster molecular shocks in NGC 1068. Gallimore et al (1996) analyzed the morphology and spectral index of the NGC 1068 jet and concluded that the radio plasma may have been diverted at a shock interface with the molecular ISM close to the AGN (knot C at r ∼ 30−40 pc). Molecular shocks in the CND could have propagated around the jet-ISM working surface.…”

Section: Tracers Of Shocks In Ngc 1068mentioning

confidence: 99%

Molecular gas chemistry in AGN

García‐Burillo

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Fuente

et al. 2010

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Context. This paper is part of a multi-species survey of line emission from the molecular gas in the circum-nuclear disk (CND) of the Seyfert 2 galaxy NGC 1068. Unlike in other active galaxies, the intensely star-forming regions in NGC 1068 and the CND can be resolved with current instrumentation. This makes this galaxy an optimal test-bed to probe the effects of AGN on the molecular medium at ∼100 pc scales. Aims. Single-dish observations have provided evidence that the abundance of silicon monoxide (SiO) in the CND of NGC 1068 is enhanced by 3-4 orders of magnitude with respect to the values typically measured in quiescent molecular gas in the Galaxy. We aim at unveiling the mechanism(s) underlying the SiO enhancement. Methods. We have imaged the emission of the SiO(2−1) (86.8 GHz) and CN(2−1) (226.8 GHz) lines in NGC 1068 at ∼150 pc and 60 pc spatial resolution with the IRAM Plateau de Bure interferometer (PdBI). We have also obtained complementary IRAM 30 m observations of HNCO and methanol (CH 3 OH) lines. These species are known as tracers of shocks in the Galaxy. Results. SiO is detected in a disk of ∼400 pc size around the AGN. SiO abundances in the CND of ∼(1−5)×10 −9 are about 1−2 orders of magnitude above those measured in the starburst ring. The overall abundance of CN in the CND is high: ∼(0.2−1) × 10 −7 . The abundances of SiO and CN are enhanced at the extreme velocities of gas associated with non-circular motions close to the AGN (r < 70 pc). On average, HNCO/SiO and CH 3 OH/SiO line ratios in the CND are similar to those measured in prototypical shocked regions in our Galaxy. Yet the strength and abundance of CN in NGC 1068 can be explained neither by shocks nor by photondominated region (PDR) chemistry. Abundances measured for CN and SiO and the correlation of CN/CO and SiO/CO ratios with hard X-ray irradiation suggest that the CND of NGC 1068 has become a giant X-ray-dominated region (XDR). Conclusions. The extreme properties of molecular gas in the circum-nuclear molecular disk of NGC 1068 result from the interplay between different processes directly linked to nuclear activity. The results presented here highlight in particular the footprint of shocks and X-ray irradiation on the properties of molecular gas in this Seyfert. Whereas XDR chemistry offers a simple explanation for CN and SiO in NGC 1068, the relevance of shocks deserves further scrutiny. The inclusion of dust grain chemistry would help solve the controversy regarding the abundances of other molecular species, like HCN, which are under-predicted by XDR models.

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“…The radio continuum resolves into a Gallimore et al 1996c) and a kiloparsec-scale radio jet that terminates in parabolic edge-brightened lobes that straddle the nucleus ( Wilson & Ulvestad 1987;Gallimore et al 1996c). The present observations marginally resolve the twin lobes after pointsource subtraction.…”

Section: Ngc 1068mentioning

confidence: 99%

A Survey of Kiloparsec-Scale Radio Outflows in Radio-Quiet Active Galactic Nuclei

et al. 2006

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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.

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The Subarcsecond Radio Structure in NGC 1068. I. Observations and Results

Cited by 145 publications

References 0 publications

Molecular gas chemistry in AGN

Molecular gas chemistry in AGN

Molecular gas chemistry in AGN

A Survey of Kiloparsec-Scale Radio Outflows in Radio-Quiet Active Galactic Nuclei

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