Chemistry in cosmic ray dominated regions

Bayet, E.; Williams, D. A.; Hartquist, T. W.; Viti, S.

doi:10.1111/j.1365-2966.2011.18500.x

Cited by 95 publications

(166 citation statements)

References 43 publications

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“…Often high abundances of particular species such as HCO + are automatically attributed to the presence of strong PDRs, since this molecule is indeed abundant in the presence of a strong UV field, regardless of the metallicity, cosmic ray ionization rate or density of the galaxy (Bayet et al 2009). Nevertheless, this species is also highly enhanced when the cosmic ray or X-ray ionization rates are high, regardless of the UV field (Bayet et al 2011;Meijerink & Spaans 2005). This apparent degeneracy is common to most molecules and again reflects the fact that chemistry is a non-linear process influenced by a combination of energetics and physical conditions.…”

Section: Introductionmentioning

confidence: 99%

Molecular line emission in NGC 1068 imaged with ALMA

Viti

García‐Burillo

Fuente

et al. 2014

A&A

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142

225

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Aims. We present a detailed analysis of Atacama Large Millimeter/submillimeter Array (ALMA) Bands 7 and 9 data of CO, HCO + , HCN, and CS, augmented with Plateau de Bure Interferometer (PdBI) data of the ∼200 pc circumnuclear disc (CND) and the ∼1.3 kpc starburst ring (SB ring) of NGC 1068, a nearby (D = 14 Mpc) Seyfert 2 barred galaxy. We aim to determine the physical characteristics of the dense gas present in the CND, and to establish whether the different line intensity ratios we find within the CND, as well as between the CND and the SB ring, are due to excitation effects (gas density and temperature differences) or to a different chemistry. Methods. We estimate the column densities of each species in local thermodynamic equilibrium (LTE). We then compute large one-dimensional, non-LTE radiative transfer grids (using RADEX) by using only the CO transitions first, and then all the available molecules to constrain the densities, temperatures, and column densities within the CND. We finally present a preliminary set of chemical models to determine the origin of the gas. Results. We find that, in general, the gas in the CND is very dense (>10 5 cm −3 ) and hot (T > 150 K), with differences especially in the temperature across the CND. The AGN position has the lowest CO/HCO + , CO/HCN, and CO/CS column density ratios. The RADEX analyses seem to indicate that there is chemical differentiation across the CND. We also find differences between the chemistry of the SB ring and some regions of the CND; the SB ring is also much colder and less dense than the CND. Chemical modelling does not succeed in reproducing all the molecular ratios with one model per region, suggesting the presence of multi-gas phase components. Conclusions. The LTE, RADEX, and chemical analyses all indicate that more than one gas-phase component is necessary to uniquely fit all the available molecular ratios within the CND. A higher number of molecular transitions at the ALMA resolution is necessary to determine quantitatively the physical and chemical characteristics of these components.

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Section: Introductionmentioning

confidence: 99%

Molecular line emission in NGC 1068 imaged with ALMA

Viti

García‐Burillo

Fuente

et al. 2014

A&A

Self Cite

142

225

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“…Though its abundance may be equally enhanced by X-ray irradiation, HCO + is shown to be abundant in the presence of UV fields (Bayet et al 2008(Bayet et al , 2011 and therefore it could be associated to the massive star formation. Additionally, HCO + is also observed to be enhanced in high velocity shocked material as observed in Galactic supernovae remnants (Dickinson et al 1980;Wootten 1981) which, again would link its enhancement to massive star formation.…”

Section: Hco + and Csmentioning

confidence: 99%

“…This has been illustrated by numerous deep spectral line surveys during the last decade (see review by Martín 2011), as well as extensive work on the theoretical modeling (e.g., Meijerink et al 2007;Bayet et al 2008Bayet et al , 2011Loenen et al 2008;Meijerink et al 2013;Harada et al 2010Harada et al , 2013. The molecular chemistry in the interstellar medium (ISM) provides direct information on the environmental conditions and therefore on the type of activity in the central few hundred parsecs of galaxies.…”

Section: Introductionmentioning

confidence: 99%

Multimolecule ALMA observations toward the Seyfert 1 galaxy NGC 1097

Martín

Kohno

Izumi

et al. 2015

A&A

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Context. The nearby Sy 1 galaxy NGC 1097 represents an ideal laboratory for exploring the molecular chemistry in the surroundings of an active galactic nucleus (AGN). Aims. Exploring the distribution of different molecular species allows us to understand the physical processes affecting the interstellar medium both in the AGN vicinity and in the outer star forming molecular ring. Methods. We carried out 3 mm ALMA observations that include seven different molecular species, namely HCN, HCO + , CCH, CS, HNCO, SiO, HC 3 N, and SO, as well as the 13 C isotopologues of the first two. Spectra were extracted from selected positions and all species were imaged over the central 2 kpc (∼30 ) of the galaxy at a resolution of ∼2.2 × 1.5 (150 pc × 100 pc). Results. HCO + and CS appear to be slightly enhanced in the star forming ring. CCH shows the largest variations across NGC 1097 and is suggested to be a good tracer of both obscured and early stage star formation. HNCO, SiO, and HC 3 N are significantly enhanced in the inner circumnuclear disk surrounding the AGN. Conclusions. Differences in the molecular abundances are observed between the star forming ring and the inner circumnuclear disk. We conclude that the HCN/HCO + and HCN/CS differences observed between AGN-dominated and starburst (SB) galaxies are not due to a HCN enhancement due to X-rays, but rather this enhancement is produced by shocked material at distances of 200 pc from the AGN. Additionally, we claim that lower HCN/CS is a combination of a small underabundance of CS in AGNs, together with excitation effects, where a high density gas component (∼10 6 cm −3 ) may be more prominent in SB galaxies. However, the most promising are the differences found among the dense gas tracers that, at our modest spatial resolution, seem to outline the physical structure of the molecular disk around the AGN. In this picture, HNCO probes the well-shielded gas in the disk, surrounding the dense material moderately exposed to the X-ray radiation traced by HC 3 N. Finally SiO might be the innermost molecule in the disk structure.

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“…In diffuse gas, Neufeld et al (2010) show that the velocity distribution of the OH + and H 2 O + absorption is dissimilar from that of H 2 O; the absorption in the molecular ions (and atomic H) being more broadly distributed in velocity space. Theoretically, the models by Bayet et al (2011) andMeijerink et al (2011) indicate that the OH + abundance is anticorrelated with the abundance of NH 3 and HCN. Furthermore, the models by Meijerink et al (2011) indicate that the H 2 O abundance is anticorrelated with ζ/n H , and thus with the abundances of OH + and H 2 O + as well.…”

Section: The Total Ionization Rate Per H Nucleus (ζ)mentioning

confidence: 99%

Excited OH⁺, H₂O⁺, and H₃O⁺in NGC 4418 and Arp 220

González-Alfonso

Fischer

Bruderer

et al. 2013

A&A

108

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We report on Herschel/PACS observations of absorption lines of OH + , H 2 O + and H 3 O + in NGC 4418 and Arp 220. Excited lines of OH + and H 2 O + with E lower of at least 285 and ∼200 K, respectively, are detected in both sources, indicating radiative pumping and location in the high radiation density environment of the nuclear regions. Abundance ratios OH + /H 2 O + of 1−2.5 are estimated in the nuclei of both sources. The inferred OH + column and abundance relative to H nuclei are (0.5−1) × 10 16 cm −2 and ∼2 × 10 −8 , respectively. Additionally, in Arp 220, an extended low excitation component around the nuclear region is found to have OH + /H 2 O + ∼ 5−10. H 3 O + is detected in both sources with N(H 3 O + ) ∼ (0.5−2) × 10 16 cm −2 , and in Arp 220 the pure inversion, metastable lines indicate a high rotational temperature of ∼500 K, indicative of formation pumping and/or hot gas. Simple chemical models favor an ionization sequence dominated by H + → O + → OH + → H 2 O + → H 3 O + , and we also argue that the H + production is most likely dominated by X-ray/cosmic ray ionization. The full set of observations and models leads us to propose that the molecular ions arise in a relatively low density ( 10 4 cm −3 ) interclump medium, in which case the ionization rate per H nucleus (including secondary ionizations) is ζ > 10 −13 s −1 , a lower limit that is several × 10 2 times the highest current rate estimates for Galactic regions. In Arp 220, our lower limit for ζ is compatible with estimates for the cosmic ray energy density inferred previously from the supernova rate and synchrotron radio emission, and also with the expected ionization rate produced by X-rays. In NGC 4418, we argue that X-ray ionization due to an active galactic nucleus is responsible for the molecular ion production.

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Chemistry in cosmic ray dominated regions

Cited by 95 publications

References 43 publications

Molecular line emission in NGC 1068 imaged with ALMA

Molecular line emission in NGC 1068 imaged with ALMA

Multimolecule ALMA observations toward the Seyfert 1 galaxy NGC 1097

Excited OH⁺, H₂O⁺, and H₃O⁺in NGC 4418 and Arp 220

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Chemistry in cosmic ray dominated regions

Cited by 95 publications

References 43 publications

Molecular line emission in NGC 1068 imaged with ALMA

Molecular line emission in NGC 1068 imaged with ALMA

Multimolecule ALMA observations toward the Seyfert 1 galaxy NGC 1097

Excited OH+, H2O+, and H3O+in NGC 4418 and Arp 220

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Excited OH⁺, H₂O⁺, and H₃O⁺in NGC 4418 and Arp 220