Photon-dominated Chemistry in the Nucleus of M82: Widespread HOC
                    <sup>+</sup>
                    Emission in the Inner 650 Parsec Disk

Fuente, A.; García‐Burillo, S.; Gérin, M.; Teyssier, D.; Usero, A.; Rizzo, J. R.; Vicente, P. de

doi:10.1086/427990

Cited by 94 publications

(103 citation statements)

References 25 publications

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“…However, these and higher [CN]/[HCN] abundance ratios have also been found in PDR/starburst scenarios (e.g. Fuente et al 2005). The fact that we find a relatively low N(CN)/N(HCN) column density ratio, with respect to what would be expected in a pure XDR scenario, could be explained by an overabundance of HCN due to the grain-surface chemistry suggested by García-Burillo et al (2008).…”

Section: Physical Environment and Abundance Ratiossupporting

confidence: 67%

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

Pérez-Beaupuits¹,

Spaans²,

Tak

et al. 2009

A&A

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Context. Single-dish observations of molecular tracers have suggested that both star formation and an AGN can drive the gas chemistry of the central ∼kpc of active galaxies. The irradiation by UV photons from an starburst or by X-rays from an AGN is expected to produce different signatures in molecular chemistry, which existing data on low-J lines cannot distinguish, as they do not trace gas at high temperature and density. Depending on the angular scale of a galaxy, the observed low-J lines can be dominated by the emission coming from the starburst ring rather than from the central region. Aims. With the incorporation of high-J molecular lines, we aim to constrain the physical conditions of the dense gas in the central region of the Seyfert 2 galaxy NGC 1068 and to determine signatures of the AGN or the starburst contribution. Methods. We used the James Clerk Maxwell Telescope to observe the J = 4−3 transition of HCN, HNC, and HCO + , as well as the CN N J = 2 5/2 − 1 3/2 and N J = 3 5/2 − 2 5/2 , in NGC 1068. We estimate the excitation conditions of HCN, HNC, and CN, based on the line intensity ratios and radiative transfer models. We discuss the results in the context of models of irradiation of the molecular gas by UV light and X-rays. Results. A first-order estimate leads to starburst contribution factors of 0.58 and 0.56 for the CN and HCN J = 1−0 lines, respectively. We find that the bulk emission of HCN, HNC, CN, and the high-J HCO + emerge from dense gas (n(H 2 ) ≥ 10 5 cm −3 ). However, the low-J HCO + lines (dominating the HCO + column density) trace less dense (n(H 2 ) < 10 5 cm −3 ) and colder (T K ≤ 20 K) gas, whereas the high-J HCO + emerges from warmer (>30 K) gas than the other molecules. We also find that the HNC/HCN and CN/HCN line intensity ratios decrease with increasing rotational quantum number J.

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Section: Physical Environment and Abundance Ratiossupporting

confidence: 67%

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

Pérez-Beaupuits¹,

Spaans²,

Tak

et al. 2009

A&A

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“…Out of these reactions, the addition, displacement (substitution), and rearrangements are important and more common where radicals are used as either reactants or intermediates. The reaction leading to the adenine formation in the interstellar space involves several simple neutral molecules and radicals such as HCN (Jiurys 2006), HCCN (Guelin & Cemicharo 1991), NH 2 CN (Turner et al 1975), and CN (Fuente et al 2005), and belongs to the second category in which both addition and atom abstraction take place. We found that the formation of adenine in the gas phase as well as in the water containing icy grains takes place in six steps.…”

Section: Resultsmentioning

confidence: 99%

“…The rate coefficient for this reaction is estimated to be 6.24 × 10 −12 cm 3 s −1 in the gas phase ( Table 2). The next step (step 4, Table 2) in the formation of the pyrimidine ring involves the closure of the incomplete ring of molecule 3 to yield molecule 4 (2,4 dihydro-3H-purine-6-amine) through the addition of a cyanide radical which is quite abundant in the interstellar space (Fuente et al 2005). The Mulliken population analysis of molecule 3 gives net atomic charges of +0.073 and -0.465 e.s.u.…”

Section: Formation Of Six-membered Pyrimidine Ringmentioning

confidence: 99%

Quantum chemical study of a new reaction pathway for the adenine formation in the interstellar space

Gupta

Tandon

Rawat

et al. 2011

A&A

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Gas phase chemistry in the cold interstellar clouds is dominated by ion-molecule and radical-radical interactions, though some neutralneutral reactions are also barrier-free and efficient at cold temperatures. It has been suggested that it is impossible to synthesize detectable abundances of the pre-biotic HCN oligomer adenine (H 5 C 5 N 5 ) in the interstellar medium via successive neutral-neutral reactions. We attempted therefore to use quantum chemical techniques to explore if adenine can possibly form in the interstellar space by radical-radical and radical-molecule interaction schemes, both in the gas phase and in the grains. We report results of ab initio calculations for the formation of adenine starting from some of the simple neutral molecules and radicals detected in the interstellar space. The reaction path is found to be totally exothermic and barrier free, which increases the probability of occurrence in the cold interstellar clouds (10−50 K). We also estimated the reaction rates.

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“…Unlike other complex molecules such as CH 3 OH, methyl acetylene shows high column densities and relative abundances in M 82 (N = 8.5 × 10 14 cm −2 , N/N H 2 = 1.1 × 10 −8 ). Since this molecule might be easily photo-dissociated by intense UV fields (Fuente et al 2005), lower abundances would have been expected in a PDR nucleus like the center of M 82. -The high J lines of HC 3 N trace the warmest gas, reaching rather high rotational temperatures of 73.3±14.0 K in NGC253 and 70.6±21.2 K in IC 342.…”

Section: Lte Analysis: Determination Of Rotational Temperaturesmentioning

confidence: 99%

“…First, its column density in M 82, of 8.5 × 10 14 cm −2 , is a factor of ∼4 larger than that of CS, and more than one order of magnitude than the HC 3 N one. Its high fractional abundance with respect to H 2 , 1.1 × 10 −8 , is puzzling for a molecule which is supposed to be easily dissociated in PDRs (Fuente et al 2005). The comparison with other molecular clouds dominated both by UV radiation and shocks, in the Galactic Center and in external galaxies, shows that M 82 is the galaxy with the highest CH 3 CCH abundance observed up to now.…”

Section: Evolved Starburst: M 82mentioning

confidence: 99%

CS, HC₃N, and CH₃CCH multi-line analyses toward starburst galaxies

Aladro

Martı́n-Pintado

Martín

et al. 2010

A&A

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Aims. We aim to study the properties of the dense molecular gas towards the inner few 100 pc of four nearby starburst galaxies dominated both by photo dissociation regions (M 82) and large-scale shocks (NGC 253, IC 342 and Maffei 2), and to relate the chemical and physical properties of the molecular clouds with the evolutionary stage of the nuclear starbursts. Methods. We have carried out multi-transitional observations and analyses of three dense gas molecular tracers, CS, HC 3 N (cyanoacetylene) and CH 3 CCH (methyl acetylene), using Boltzmann diagrams in order to determine the rotational temperatures and column densities of the dense gas, and using a Large Velocity Gradients model to calculate the H 2 density structure in the molecular clouds.Results. The CS and HC 3 N data indicate the presence of density gradients in the molecular clouds. These two molecules show similar excitation conditions, suggesting that they arise from the same gas components. In M 82, CH 3 CCH has the highest fractional abundance determined in a extragalactic source (1.1 × 10 −8 ). Conclusions. The density and the chemical gradients we have found in all galaxies can be explained in the framework of the starburst evolution, which affects the chemistry and the structure of molecular clouds around the galactic nuclei. The young shock-dominated starburst galaxies, like presumably Maffei 2, show a cloud structure with a rather uniform density and chemical composition which suggests low star formation activity. Molecular clouds in galaxies with starburst in an intermediate stage of evolution, such as NGC 253 and IC 342, show clouds with a large density contrast (two orders of magnitude) between the denser regions (cores) and the less dense regions (halos) of the molecular clouds and relatively constant chemical abundance. Finally, the galaxy with the most evolved starburst, M 82, has clouds with a rather uniform density structure, large envelopes of atomic/molecular gas subjected to UV photodissociating radiation from young star clusters, and very different chemical abundances of HC 3 N and CH 3 CCH.

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Photon-dominated Chemistry in the Nucleus of M82: Widespread HOC ⁺ Emission in the Inner 650 Parsec Disk

Cited by 94 publications

References 25 publications

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

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

Quantum chemical study of a new reaction pathway for the adenine formation in the interstellar space

CS, HC₃N, and CH₃CCH multi-line analyses toward starburst galaxies

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Photon-dominated Chemistry in the Nucleus of M82: Widespread HOC + Emission in the Inner 650 Parsec Disk

Cited by 94 publications

References 25 publications

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

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

Quantum chemical study of a new reaction pathway for the adenine formation in the interstellar space

CS, HC3N, and CH3CCH multi-line analyses toward starburst galaxies

Contact Info

Product

Resources

About

Photon-dominated Chemistry in the Nucleus of M82: Widespread HOC ⁺ Emission in the Inner 650 Parsec Disk

CS, HC₃N, and CH₃CCH multi-line analyses toward starburst galaxies