Probing X-ray irradiation in the nucleus of NGC 1068 with observations of high-<i>J</i>lines of dense gas tracers

Pérez-Beaupuits, J. P.; Spaans, Marco; Tak, F. F. S. van der; Aalto, S.; García‐Burillo, S.; Fuente, A.; Usero, A.

doi:10.1051/0004-6361/200912350

Cited by 35 publications

(52 citation statements)

References 37 publications

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“…Others have been assuming smaller source sizes such as 1. 5 (Pérez-Beaupuits et al 2009), but we have found that a smaller source size does not significantly change our results for the physical conditions of the CND. For the rest of this paper, we will be focusing on high-density tracer emission from the CND, but first we find it appropriate to comment on the most prominent feature of our spectrum, 12 CO J = 2 → 1, mostly from the SB ring.…”

Section: Spectrum Resultscontrasting

confidence: 58%

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The Dense Molecular Gas in the Circumnuclear Disk of NGC 1068

Kamenetzky¹,

Glenn²,

Maloney³

et al. 2011

ApJ

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We present a 190-307 GHz broadband spectrum obtained with Z-Spec of NGC 1068 with new measurements of molecular rotational transitions. After combining our measurements with those previously published and considering the specific geometry of this Seyfert 2 galaxy, we conduct a multi-species Bayesian likelihood analysis of the density, temperature, and relative molecular abundances of HCN, HNC, CS, and HCO + . We find that these molecules trace warm (T > 100 K) gas of H 2 number densities 10 4.2 -10 4.9 cm −3 . Our models also place strong constraints on the column densities and relative abundances of these molecules, as well as on the total mass in the circumnuclear disk. Using the uniform calibration afforded by the broad Z-Spec bandpass, we compare our line ratios to X-raydominated region (XDR) and photon-dominated region models. The majority of our line ratios are consistent with the XDR models at the densities indicated by the likelihood analysis, lending substantial support to the emerging interpretation that the energetics in the circumnuclear disk of NGC 1068 are dominated by accretion onto an active galactic nucleus.

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Section: Spectrum Resultscontrasting

confidence: 58%

“…Several recent studies indicate that the CND of NGC 1068 is an XDR (Usero et al 2004;Pérez-Beaupuits et al 2009;Krips et al 2008;Garcia-Burillo et al 2010). There are a variety of diagnostics of XDR/PDR environments that can be utilized with millimeter-range molecular transitions.…”

Section: Introductionmentioning

confidence: 96%

The Dense Molecular Gas in the Circumnuclear Disk of NGC 1068

Kamenetzky¹,

Glenn²,

Maloney³

et al. 2011

ApJ

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“…For simplicity we restricted H 2 densities to lie within the same range values explored for SiO. Pérez-Beaupuits et al (2009), based on a multi-transition CN analysis, have derived a more restricted density range (n(H 2 ) = 10 6±1 cm −3 ), which nevertheless lies within the range explored here. In the first scenario we need about an order of magnitude increase in n(H 2 ) to fit the progression of ratios from low-velocities to high-velocities (see Fig.…”

Section: Sio Abundancesmentioning

confidence: 96%

“…By contrast, current gas-phase XDR models successfully reproduce the SiO abundances derived in NGC 1068 without resorting to dust grain chemistry. Nonetheless, the inclusion of dust grain chemistry, likely linked to the mechanical heating of the molecular ISM, would help solve the controversy regarding the abundances of species like HCN and HNC, under-predicted by XDR schemes Loenen et al 2008;Pérez-Beaupuits et al 2009). Actually, while CN is overly produced in gas-phase XDR models, HCN is under-produced with respect to the level required by observations in AGNs.…”

Section: X-ray Chemistry In Ngc 1068mentioning

confidence: 99%

Molecular gas chemistry in AGN

García‐Burillo

Usero

Fuente

et al. 2010

A&A

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126

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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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“…As mentioned before, we initiate the molecular cloud with turbulent conditions that are typical for an active environment, FWHM = 5 km s −1 , or σ turb = 2.1 km s −1 (Pérez-Beaupuits et al 2009), and apply this over all scales with a power spectrum of P(k) ∝ k −4 , following the empirical laws for compressible fluids (Larson 1981;Myers & Gammie 1999;Heyer & Brunt 2004). This scaling is also known as Burgers turbulence (Burgers 1939;Bec & Khanin 2007).…”

Section: Initial Conditionsmentioning

confidence: 99%

The impact of magnetic fields on the IMF in star-forming clouds near a supermassive black hole

Hocuk

Schleicher

Spaans

et al. 2012

A&A

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Star formation in the centers of galaxies is thought to yield massive stars with a possibly top-heavy stellar mass distribution. It is likely that magnetic fields play a crucial role in the distribution of stellar masses inside star-forming molecular clouds. In this context, we explore the effects of magnetic fields, with a typical field strength of 38 μG, such as in RCW 38, and a field strength of 135 μG, similar to NGC 2024 and the infrared dark cloud G28.34+0.06, on the initial mass function (IMF) near (≤10 pc) a 10 7 solar mass black hole. Using these conditions, we perform a series of numerical simulations with the hydrodynamical code FLASH to elucidate the impact of magnetic fields on the IMF and the star-formation efficiency (SFE) emerging from an 800 solar mass cloud. We find that the collapse of a gravitationally unstable molecular cloud is slowed down with increasing magnetic field strength and that stars form along the field lines. The total number of stars formed during the simulations increases by a factor of 1.5−2 with magnetic fields. The main component of the IMF has a lognormal shape, with its peak shifted to sub-solar (≤0.3 M ) masses in the presence of magnetic fields, due to a decrease in the accretion rates from the gas reservoir. In addition, we see a top-heavy, nearly flat IMF above ∼2 solar masses, from regions that were supported by magnetic pressure until high masses are reached. We also consider the effects of X-ray irradiation if the central black hole is active. X-ray feedback inhibits the formation of sub-solar masses and decreases the SFEs even further. Thus, the second contribution is no longer visible. We conclude that magnetic fields potentially change the SFE and the IMF both in active and inactive galaxies, and need to be taken into account in such calculations. The presence of a flat component of the IMF would be a particularly relevant signature for the importance of magnetic fields, as it is usually not found in hydrodynamical simulations.

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Probing X-ray irradiation in the nucleus of NGC 1068 with observations of high-Jlines of dense gas tracers

Cited by 35 publications

References 37 publications

The Dense Molecular Gas in the Circumnuclear Disk of NGC 1068

The Dense Molecular Gas in the Circumnuclear Disk of NGC 1068

Molecular gas chemistry in AGN

The impact of magnetic fields on the IMF in star-forming clouds near a supermassive black hole

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