Nuclear Abundances and Evolution of the Interstellar Medium

Wannier, P. G.

doi:10.1146/annurev.aa.18.090180.002151

Cited by 128 publications

(67 citation statements)

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“…We measured 12 C/ 13 C ratios in the wide range of 15−45. This result agrees with the values reported toward the Sgr A region (Audouze et al 1975;Wannier 1980) and is consistent with the scenario of 13 C enrichment toward the Galactic center region (Wilson & Rood 1994;Wilson 1999).…”

Section: Cn: Carbon 12 C/ 13 C Isotopic Ratiosupporting

confidence: 92%

Surviving the hole

Martín

Martı́n-Pintado

Montero-Castaño

et al. 2012

A&A

119

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Context. The interstellar region within the few central parsecs around the super-massive black hole, Sgr A * , at the very Galactic center is composed of a number of overlapping molecular structures that are subject to one of the most hostile physical environments in the Galaxy. Aims. Through the study of the morphology and kinematics of the emission from different molecular species as well as the variation of their line ratios we can attain a deeper understanding of the distribution and interaction between different gas structures and the energetic phenomena taking place in the surroundings of Sgr A * and of the physical processes responsible for the heating in this region. Methods. We performed high-resolution (4 × 3 ∼ 0.16 × 0.11 pc) interferometric observations of CN, 13 CN, H 2 CO, SiO, c-C 3 H 2 and HC 3 N emission at 1.3 mm toward the central ∼4 pc of the Galactic center region. Results. Strong differences are observed in the distribution of the different molecules. The UV resistant species CN, the only species tracing all previously identified circumnuclear disk (CND) structures, is mostly concentrated in optically thick clumps in the rotating filaments around Sgr A * . H 2 CO emission traces a shell-like structure that we interpret as the expansion of Sgr A East against the 50 km s −1 and 20 km s −1 giant molecular clouds (GMCs). We derive isotopic ratios 12 C/ 13 C ∼ 15−45 across most of the CND region, except for the northeast arm, where the peak of H 2 CO is observed and ratios <10 are found. The densest molecular material, traced by SiO and HC 3 N, is located in the southern CND, likely because of shocked gas infalling from the 20 km s −1 GMC streamers, and the northeast arm, as a result of the expansion of Sgr A East or a connecting point of the 50 km s −1 streamer east of the CND. The observed c-C 3 H 2 /HC 3 N ratio observed in the region is more than an order of magnitude lower than in Galactic PDRs. Toward the central region only CN was detected in absorption. In addition to the known narrow line-of-sight absorptions, a 90 km s −1 wide optically thick spectral feature is observed. We found evidence of an even wider (>100 km s −1 ) absorption feature. About 70−75% of the gas mass, concentrated in just the 27% densest molecular clumps, is associated with rotating structures and show evidence of an association with each of the arcs of ionized gas in the mini-spiral structure. Conclusions. These observations provide a combined chemical and kinematical picture of the very central region around Sgr A * . Chemical differentiation has been proven to be a powerful tool to distinguish the many overlapping molecular components in this crowded and heavily obscured region.

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Section: Cn: Carbon 12 C/ 13 C Isotopic Ratiosupporting

confidence: 92%

Surviving the hole

Martín

Martı́n-Pintado

Montero-Castaño

et al. 2012

A&A

119

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“…In our case we took the CND values estimated by U04 from the multiline 30 m survey of NGC 1068: n(H 2 ) ∼ 10 5 cm −3 and T K = 50 K. As a second assumption we took a standard abundance for H 13 CO + = 2.5×10 −10 and derived X(SiO) from the SiO/H 13 CO + column density ratio fitted by LVG. In our case this corresponds to a typical abundance of the main isotope X(H 12 CO + ) = 10 −8 , and to an isotopic ratio [ 12 C]/[ 13 C] 40, similar to the values found in the CND of our Galaxy (Wannier 1980). The derived abundance of SiO in the CND is ∼2.2 × 10 −9 .…”

Section: Sio/h 13 Co + Ratiossupporting

confidence: 86%

Molecular gas chemistry in AGN

García‐Burillo

Usero

Fuente

et al. 2010

A&A

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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“…Therefore this value can be taken as a conservative lower limit for T K . Furthermore, we adopt in our calculations an isotopic ratio of 12 C/ 13 C = 40 (Wannier 1980). It has been previously reported that LVG models of CO emission in PDR-type environments can lead to inconsistencies related to spatial fine structure, density and kinetic temperature (see the case of M 82 in Mao et al 2000).…”

Section: Lvg Modelsmentioning

confidence: 99%

Molecular gas chemistry in AGN

Usero

García‐Burillo

Fuente

et al. 2004

A&A

180

293

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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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Nuclear Abundances and Evolution of the Interstellar Medium

Cited by 128 publications

References 1 publication

Surviving the hole

Surviving the hole

Molecular gas chemistry in AGN

Molecular gas chemistry in AGN

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