Surface chemistry in the interstellar medium

Bron, Emeric; Bourlot, J. Le; Petit, Franck

doi:10.1051/0004-6361/201322101

Cited by 82 publications

(118 citation statements)

References 50 publications

(69 reference statements)

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“…The proposed photolytic route, which has been measured in the laboratory (e.g., Smith 1984;Adel et al 1989;Marée et al 1996;Godard et al 2011;Alata et al 2014), could act in conjunction with and complement other formation mechanisms (e.g., Hollenbach & Salpeter 1971;Rauls & Hornekaer 2008;Le Page et al 2009;Bron et al 2014). We have continued this work with an investigation of the effects of grain charging and the complimentary effects of gas heating, via photo-electron emission, and gas cooling (Bocchio et al, in prep.).…”

Section: Dust Evolution In Pdrs and Hii Regionsmentioning

confidence: 91%

The global dust modelling framework THEMIS

Jones

Koehler

Ysard

et al. 2017

A&A

241

330

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Here we introduce the interstellar dust modelling framework THEMIS (The Heterogeneous dust Evolution Model for Interstellar Solids), which takes a global view of dust and its evolution in response to the local conditions in interstellar media. This approach is built upon a core model that was developed to explain the dust extinction and emission in the diffuse interstellar medium. The model was then further developed to self-consistently include the effects of dust evolution in the transition to denser regions. The THEMIS approach is under continuous development and we are currently extending the framework to explore the implications of dust evolution in HII regions and the photon-dominated regions associated with star formation. We provide links to the THEMIS, DustEM and DustPedia websites where more information about the model, its input data and applications can be found.

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Section: Dust Evolution In Pdrs and Hii Regionsmentioning

confidence: 91%

The global dust modelling framework THEMIS

Jones

Koehler

Ysard

et al. 2017

A&A

241

330

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“…The Meudon PDR code 2 is described in Le Petit et al (2006), Le Bourlot et al (2012), and Bron et al (2014). It computes the atomic and molecular structure of interstellar clouds.…”

Section: The Meudon Pdr Modelmentioning

confidence: 99%

A milestone toward understanding PDR properties in the extreme environment of LMC-30 Doradus

Chevance

Madden

Lebouteiller

et al. 2016

A&A

103

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Context. More complete knowledge of galaxy evolution requires understanding the process of star formation and the interaction between the interstellar radiation field and interstellar medium (ISM) in galactic environments traversing a wide range of physical parameter space. We focus on the impact of massive star formation on the surrounding low metallicity ISM in 30 Doradus in the Large Magellanic Cloud (LMC). A low metal abundance, which can characterizes some galaxies of the early Universe, results in less ultraviolet (UV) shielding for the formation of the molecular gas necessary for star formation to proceed. The half-solar metallicity gas in this region is strongly irradiated by the super star cluster R136, making it an ideal laboratory to study the structure of the ISM in an extreme environment. Aims. Our goal is to construct a comprehensive, self-consistent picture of the density, radiation field, and ISM structure in the most active star-forming region in the LMC, 30 Doradus. Our spatially resolved study investigates the gas heating and cooling mechanisms, particularly in the photodissociation regions (PDR) where the chemistry and thermal balance are regulated by far-UV photons (6 eV < hν < 13.6 eV). Methods. We present Herschel observations of far-infrared (FIR) fine-structure lines obtained with PACS and SPIRE/FTS. We combined atomic fine-structure lines from Herschel and Spitzer observations with ground-based CO data to provide diagnostics on the properties and structure of the gas by modeling it with the Meudon PDR code. For each tracer we estimate the possible contamination from the ionized gas to isolate the PDR component. We derive the spatial distribution of the radiation field, the pressure, the size, and the filling factor of the photodissociated gas and molecular clouds. Results. We find a range of pressure of ∼10 5 −1.7×10 6 cm −3 K and a range of incident radiation field G UV ∼ 10 2 −2.5×10 4 through PDR modeling. Assuming a plane-parallel geometry and a uniform medium, we find a total extinction A max V of 1-3 mag, which corresponds to a PDR cloud size of 0.2 to 3pc with small CO depth scale of 0.06 to 0.5 pc. At least 90% of the [C ii] originates in PDRs in this region, while a significant fraction of the L FIR (up to 70% in some places) can be associated with an ionized gas component. Theratio (2 to 60) throughout the observed map, correlated with the filling factor, reveals the porosity of the ISM in this region, which is traversed by hard UV photons surrounding small PDR clumps. We also determine the three-dimensional structure of the gas, showing that the clouds are distributed 20 to 80 pc away from the main ionizing cluster, R136.

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“…We use the outcomes of these models in tabular form, from which we extract the temperatures for our simulations. Temperature fluctuations of dust grains are not considered in this model, because Bron et al (2014) showed that their effect on the H 2 formation rate is limited.…”

Section: Computationsmentioning

confidence: 99%

H₂formation on PAHs in photodissociation regions: a high-temperature pathway to molecular hydrogen

Boschman

Cazaux

Spaans

et al. 2015

A&A

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Aims. Molecular hydrogen is the most abundant molecule in the Universe. It is thought that a large portion of H 2 forms by association of hydrogen atoms to polycyclic aromatic hydrocarbons (PAHs). We model the influence of PAHs on total H 2 formation rates in photodissociation regions (PDRs) and assess the effect of these formation rates on the total cloud structure. Methods. We set up a chemical kinetic model at steady state in a PDR environment and included radiative transfer to calculate the chemistry at different depths in the PDR. This model includes known dust grain chemistry for the formation of H 2 and a H 2 formation mechanism on PAHs. Since H 2 formation on PAHs is impeded by thermal barriers, this pathway is only efficient at higher temperatures (T > 200 K). At these temperatures the conventional route of H 2 formation via H atoms physisorbed on dust grains is no longer feasible, so the PAH mechanism enlarges the region where H 2 formation is possible. Results. We find that PAHs have a significant influence on the structure of PDRs. The extinction at which the transition from atomic to molecular hydrogen occurs strongly depends on the presence of PAHs, especially for PDRs with a strong external radiation field. A sharp spatial transition between fully dehydrogenated PAHs on the outside of the cloud and normally hydrogenated PAHs on the inside is found. As a proof of concept, we use coronene to show that H 2 forms very efficiently on PAHs, and that this process can reproduce the high H 2 formation rates derived in several PDRs.

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Surface chemistry in the interstellar medium

Cited by 82 publications

References 50 publications

The global dust modelling framework THEMIS

The global dust modelling framework THEMIS

A milestone toward understanding PDR properties in the extreme environment of LMC-30 Doradus

H₂formation on PAHs in photodissociation regions: a high-temperature pathway to molecular hydrogen

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Surface chemistry in the interstellar medium

Cited by 82 publications

References 50 publications

The global dust modelling framework THEMIS

The global dust modelling framework THEMIS

A milestone toward understanding PDR properties in the extreme environment of LMC-30 Doradus

H2formation on PAHs in photodissociation regions: a high-temperature pathway to molecular hydrogen

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H₂formation on PAHs in photodissociation regions: a high-temperature pathway to molecular hydrogen