The velocity profile of the 1 - 0 S(1) line of molecular hydrogen at Peak 1 in Orion

Context. Grain-grain processing has been shown to be an indispensable ingredient of shock modelling in high density environments. For densities higher than ∼10 5 cm −3 , shattering becomes a self-enhanced process that imposes severe chemical and dynamical consequences on the shock characteristics. Shattering is accompanied by the vaporization of grains, which can, in addition to sputtering, directly release SiO to the gas phase. Given that SiO rotational line radiation is used as a major tracer of shocks in dense clouds, it is crucial to understand the influence of vaporization on SiO line emission. Aims. We extend our study of the impact of grain-grain processing on C-type shocks in dense clouds. Various values of the magnetic field are explored. We study the corresponding consequences for molecular line emission and, in particular, investigate the influence of shattering and related vaporization on the rotational line emission of SiO. Methods. We have developed a recipe for implementing the effects of shattering and vaporization into a 2-fluid shock model, resulting in a reduction of computation time by a factor ∼100 compared to a multi-fluid modelling approach. This implementation was combined with an LVG-based modelling of molecular line radiation transport. Using this combined model we calculated grids of shock models to explore the consequences of different dust-processing scenarios. Results. Grain-grain processing is shown to have a strong influence on C-type shocks for a broad range of magnetic fields: the shocks become hotter and thinner. The reduction in column density of shocked gas lowers the intensity of molecular lines, at the same time as higher peak temperatures increase the intensity of highly excited transitions compared to shocks without grain-grain processing. For OH the net effect is an increase in line intensities, while for CO and H 2 O it is the contrary. The intensity of H 2 emission is decreased in low transitions and increased for highly excited lines. For all molecules, the highly excited lines become sensitive to the value of the magnetic field. Although vaporization increases the intensity of SiO rotational lines, this effect is weakened by the reduced shock width. The release of SiO early in the hot shock changes the excitation characteristics of SiO radiation, although it does not yield an increase in width for the line profiles. To significantly increase the intensity and width of SiO rotational lines, SiO needs to be present in grain mantles.

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“…Similarly, the lines would be broadened by the velocity profile associated with a bow shock (e.g. Brand et al 1989). …”

Section: Sio Rotational Line Profilesmentioning

confidence: 99%

Shocks in dense clouds

Anderl

Guillet

Forêts

et al. 2013

A&A

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“…Simplified theoretical models of bowshocks have been constructed, following the work of Hartigan et al (1987). Brand et al (1989) constructed a model for a J shock, and derived an analytical solution for the emission profile of the complete bow that displayed the major features and shortcomings of this type of shock model. The principle result is that the profile, although spanning the large range of velocity equal to the value of the flow at infinity, has very concave wings, easily disguised in data with typical values of signal to noise ratio.…”

Section: The Bow Shock Modelmentioning

confidence: 99%

“…Following these discoveries, much attention has been paid to the dynamics of the OMC-1 region, especially the nature of the molecular shocks (e.g. Nadeau, Neugebauer & Geballe 1982;Brand et al 1988Brand et al , 1989. The first models to explain the excitation relied on planar hydrodynamic J shocks (Hollenbach & Shull 1977;Kwan 1977;London et al 1977).…”

Section: Introductionmentioning

confidence: 99%

Velocity-resolved Fabry-Perot imaging of molecular hydrogen emission in OMC-1

Chrysostomou

Burton

Axon

et al. 1997

Monthly Notices of the Royal Astronomical Society

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“…To remove the effect of the / ratio, Mouri (1994) compares different excitation models using the intensity ratios of 2-1 S(1)/1-0 S(1) (which occur for molecules) and 1-0 S(2)/1-0 S(0) (for molecules), where non-thermal values are expected to be constant. The line ratios for NGC 6951 suggests that its nucleus has thermal excitation and that regions 2, 3 and 4 lie closest to the theoretical point of the shock heating process (Brand et al 1989), establishing a possible distinction from region 1, which is compatible with X-ray excitation (Lepp & McCray 1983). The gas interaction with the shock driving source may be more evident in region 2, which is brighter than region 1.…”

Section: Physical Conditions Of the Molecular Gasmentioning

confidence: 64%

Digging process in NGC 6951: the molecular disc bumped by the jet

May

Steiner

Ricci

et al. 2016

Mon. Not. R. Astron. Soc.

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We present a study of the central 200 pc of the galaxy NGC 6951, SAB(rs)bc, an active twin of the Milky Way, at a distance of 24 Mpc. Its nucleus has been observed in the optical with the GMOS-IFU, showing an outflow, and with the HST/ACS, revealing two extended structures with similar orientation, suggesting the presence of a collimating and/or obscuring structure. In order to ascertain this hypothesis, adaptive optics assisted NIR integral field spectroscopic observations were obtained with the NIFS spectrograph in the Gemini North telescope. We detected a compact structure of H 2 molecular gas, interpreted as a nearly edgeon disc with diameter of ∼47 pc, PA=124°and velocity range from-40 to +40 km s −1. This disc is misaligned by 32°with respect to the radio jet and the ionization cones seen in the optical. There are two regions of turbulent gas, with position angles similar to the jet/cones, seen both in molecular and ionized phases; these regions are connected to the edges of the molecular disc and coincide with a high ratio of [N II]/Hα=5, suggesting that these regions are shock excited, partially ionized or both. We explain these structures as a consequence of a "digging process" that the jet inflicts on the disc, ejecting the molecular gas towards the ionization cones. The dynamical mass within 17 pc is estimated as 6.3 × 10 6 M. This is an interesting case of an object presenting evidence of a connected feeding-feedback structure.

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The velocity profile of the 1 - 0 S(1) line of molecular hydrogen at Peak 1 in Orion

Cited by 39 publications

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Shocks in dense clouds

Shocks in dense clouds

Velocity-resolved Fabry-Perot imaging of molecular hydrogen emission in OMC-1

Digging process in NGC 6951: the molecular disc bumped by the jet

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