Molecular tracers of filamentary CO emission regions surrounding the central galaxies of clusters

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

doi:10.1051/0004-6361/200913185

Cited by 13 publications

(23 citation statements)

References 26 publications

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“…The infiltration of ICM X-ray gas into the molecular gas can reduce, through grain sputtering, the dust content, which in turn affects the H 2 formation rate and thus the [CO/H 2 ] abundance. As shown by Bayet et al (2010), highly energetic particles can have a significant effect on the chemistry of the molecular gas, altering the abundance of various molecules (although apparently not CO). The gas chemistry also depends on the gas temperature; in §5.1, we showed that the molecular gas traced by CO in NGC 1275 can have a higher characteristic temperature than that of Galactic GMCs.…”

Section: Turbulent Structuresmentioning

confidence: 99%

The Role of Electron Excitation and Nature of Molecular Gas in Cluster Central Elliptical Galaxies

Lim

Dinh-V-Trung

Vrtilek³

et al. 2017

ApJ

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We present observations in CO(3-2) that, combined with previous observations in CO(2-1), constrain the physical properties of the filamentary molecular gas in the central ∼6.5 kpc of NGC 1275, the central giant elliptical galaxy of the Perseus cluster. We find this molecular gas to have a temperature 20 K and a density ∼10 2 -10 4 cm −3 , typically warmer and denser than the bulk of Giant Molecular Clouds (GMCs) in the Galaxy. Bathed in the harsh radiation and particle field of the surrounding intracluster X-ray gas, the molecular gas likely has a much higher ionization fraction than that of GMCs. For an ionization fraction of ∼10 −4 , similar to that of Galactic diffuse ( 250 cm −3 ) partially-molecular clouds that emit in HCN(1-0) and HCO + (1-0), we show that the same gas traced in CO can produce the previously reported emissions in HCN(3-2), HCO + (3-2), and CN(2-1) from NGC 1275; the dominant source of excitation for all the latter molecules is collisions with electrons. To prevent collapse, as evidenced by the lack of star formation in the molecular filaments, they must consist of thin strands that have crosssectional radii 0.2-2 pc if supported solely by thermal gas pressure; larger radii are permissible if turbulence or poloidal magnetic fields provide additional pressure support. We point out that the conditions required to relate CO luminosities to molecular gas masses in our Galaxy are unlikely to apply in cluster central elliptical galaxies. Rather than being virialized structures analogous to GMCs, we propose that the molecular gas in NGC 1275 comprises pressure-confined structures created by turbulent flows.

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Section: Turbulent Structuresmentioning

confidence: 99%

The Role of Electron Excitation and Nature of Molecular Gas in Cluster Central Elliptical Galaxies

Lim

Dinh-V-Trung

Vrtilek³

et al. 2017

ApJ

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“…In the present work, the code is used to determine the chemical and thermal properties at all depths up to 20 visual magnitudes. For the present work, and consistent with the Bayet et al (2010) version of the code, additional radiative cooling due to rotational transitions of 13 CO, C 18 O, CS, OH and H 2 O have been implemented. The escape probability formalism of de Jong, Boland & Dalgarno (1980) is used to determine non‐local thermodynamic equilibrium level populations and resulting line intensities at each depth‐ and time‐step, in the same manner as for the existing coolants in the code.…”

Section: Model Descriptionmentioning

confidence: 99%

“…The ucl_pdr code also includes cooling due to the O i metastable levels, and the O–H + collisions and O–e − collisions which excite them; these are important for the models for high values of ζ. The treatment of H 2 self‐shielding has also been updated to use the results of detailed calculations performed by Lee et al (1996), as described in Bayet et al (2010). The chemical network links 131 species in over 1834 gas‐phase reactions; only H 2 is formed by surface chemistry; freeze‐out of species on to grain surfaces is excluded.…”

Section: Model Descriptionmentioning

confidence: 99%

Chemistry in cosmic ray dominated regions

Bayet

Williams

Hartquist

et al. 2011

Monthly Notices of the Royal Astronomical Society

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158

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Molecular line observations may serve as diagnostics of the degree to which the number density of cosmic ray protons, having energies of 10s to 100s of MeV each, is enhanced in starburst galaxies and galaxies with active nuclei. Results, obtained with the ucl_pdr code, for the fractional abundances of molecules as functions of the cosmic ray induced ionization rate, ζ, are presented. The aim is not to model any particular external galaxies. Rather, it is to identify characteristics of the dependencies of molecular abundances on ζ, in part to enable the development of suitable observational programmes for cosmic ray dominated regions (CRDRs) which will then stimulate detailed modelling. For a number density of hydrogen nuclei of of 104 cm−3, and high visual extinction, the fractional abundances of some species increase as ζ increases to 10−14 s−1, but for much higher values of ζ the fractional abundances of all molecular species are significantly below their peak values. We show in particular that OH, H2O, H+3, H3O+ and OH+ attain large fractional abundances (≥10−8) for ζ as large as 10−12 s−1. HCO+ is a poor tracer of CRDRs when ζ > 10−13 s−1. Sulphur‐bearing species may be useful tracers of CRDR gas in which ζ∼ 10−16 s−1. Ammonia has a large fractional abundance for ζ≤ 10−16 s−1 and nitrogen appears in CN‐bearing species at significant levels as ζ increases, even up to ∼10−14 s−1. In this paper, we also discuss our model predictions, comparing them to recent detections in both Galactic and extragalactic sources. We show that they agree well, to a first approximation, with the observational constraints.

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“…In modeling cooling, both methods include emission by C, C + , and O fine structure lines, gas-grain collisional cooling, cooling by rotational lines of CO, and H 2 collisional dissociation, but 3d-pdr neglects H 2 and H 2 O ro-vibrational and OH rotational lines, which are included in the one-dimensional code ucl_pdr (Bayet et al 2010), as well as H collisional ionization and Compton cooling. However, these lines do not produce significant cooling under the conditions considered here, and so neglecting them is a good approximation.…”

Section: Code Comparison: Post-processing Versus In Situ Calculationmentioning

confidence: 99%

Modeling the Atomic-to-Molecular Transition and Chemical Distributions of Turbulent Star-Forming Clouds

Offner

Bisbas

Viti

et al. 2013

ApJ

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We use 3d-pdr, a three-dimensional astrochemistry code for modeling photodissociation regions (PDRs), to post-process hydrodynamic simulations of turbulent, star-forming clouds. We focus on the transition from atomic to molecular gas, with specific attention to the formation and distribution of H, C + , C, H 2 , and CO. First, we demonstrate that the details of the cloud chemistry and our conclusions are insensitive to the simulation spatial resolution, to the resolution at the cloud edge, and to the ray angular resolution. We then investigate the effect of geometry and simulation parameters on chemical abundances and find weak dependence on cloud morphology as dictated by gravity and turbulent Mach number. For a uniform external radiation field, we find similar distributions to those derived using a one-dimensional PDR code. However, we demonstrate that a three-dimensional treatment is necessary for a spatially varying external field, and we caution against using one-dimensional treatments for non-symmetric problems. We compare our results with the work of Glover et al., who self-consistently followed the time evolution of molecule formation in hydrodynamic simulations using a reduced chemical network. In general, we find good agreement with this in situ approach for C and CO abundances. However, the temperature and H 2 abundances are discrepant in the boundary regions (A v 5), which is due to the different number of rays used by the two approaches.

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Molecular tracers of filamentary CO emission regions surrounding the central galaxies of clusters

Cited by 13 publications

References 26 publications

The Role of Electron Excitation and Nature of Molecular Gas in Cluster Central Elliptical Galaxies

The Role of Electron Excitation and Nature of Molecular Gas in Cluster Central Elliptical Galaxies

Chemistry in cosmic ray dominated regions

Modeling the Atomic-to-Molecular Transition and Chemical Distributions of Turbulent Star-Forming Clouds

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