Régions Ioniséesémission Radio Des Régions H Ii

Cesarsky, D.; Squeren, A. M. Le

doi:10.1051/jphyscol:1978126

Cited by 57 publications

(92 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The static magnetic field outside denser regions is assumed to be much smaller than the field inside these regions. Because the difference between the magnetic field inside and outside the cloud significantly dampens the Alfvén waves for mid to high energy cosmic rays, E 0 cannot be greater than 50 MeV (Cesarsky & Volk 1978). E 0 is dependent on various physical parameters of the source in question.…”

Section: Magnetic Field Effectsmentioning

confidence: 99%

Observing a column-dependentζin dense interstellar sources: the case of the Horsehead nebula

Rimmer

Herbst

Morata

et al. 2011

A&A

View full text Add to dashboard Cite

Context. Observations of small carbon-bearing molecules such as CCH, C 4 H, c-C 3 H 2 , and HCO in the Horsehead nebula have shown these species to have higher abundances towards the edge of the source than towards the center. Aims. Given the determination of a wide range of values for ζ (s −1 ), the total ionization rate of hydrogen atoms, and the proposal of a column-dependent ζ(N H ), where N H is the total column of hydrogen nuclei, we desire to determine if the effects of ζ(N H ) in a single object with spatial variation can be observable. We chose the Horsehead nebula because of its geometry and high density. Methods. We model the Horsehead nebula as a near edge-on photon dominated region (PDR), using several choices for ζ, both constant and as a function of column. The column-dependent ζ functions are determined by a Monte Carlo model of cosmic ray penetration, using a steep power-law spectrum and accounting for ionization and magnetic field effects. We consider a case with low-metal elemental abundances as well as a sulfur-rich case.Results. We show that use of a column-dependent ζ(N H ) of 5 × 10 −15 s −1 at the surface and 7.5 × 10 −16 s −1 at A V = 10 on balance improves agreement between measured and theoretical molecular abundances, compared with constant values of ζ.

show abstract

Section: Magnetic Field Effectsmentioning

confidence: 99%

Observing a column-dependentζin dense interstellar sources: the case of the Horsehead nebula

Rimmer

Herbst

Morata

et al. 2011

A&A

View full text Add to dashboard Cite

show abstract

“…The transport equation along the flux tube can be written as (Cesarsky & Völk 1978;Enßlin 2003), where we dropped the injection term q and the catastrophic losses. The magnetic field enters the transport equation since magnetic mirrors reflect particles away from locations with converging field lines, so that the CR population tries to establish a constant density per volume, and not per magnetic flux.…”

Section: Cr Transportmentioning

confidence: 99%

Cosmic ray transport in galaxy clusters: implications for radio halos, gamma-ray signatures, and cool core heating

Enßlin

Pfrommer

Miniati

et al. 2011

A&A

199

294

View full text Add to dashboard Cite

We investigate the interplay of cosmic ray (CR) propagation and advection in galaxy clusters. Propagation in form of CR diffusion and streaming tends to drive the CR radial profiles towards being flat, with equal CR number density everywhere. Advection of CR by the turbulent gas motions tends to produce centrally enhanced profiles. We assume that the CR streaming velocity is of the order of the sound velocity. This is motivated by plasma physical arguments. The CR streaming is then usually larger than typical advection velocities and becomes comparable or lower than this only for periods with trans-and super-sonic cluster turbulence. As a consequence a bimodality of the CR spatial distribution results. Strongly turbulent, merging clusters should have a more centrally concentrated CR energy density profile with respect to relaxed ones with very subsonic turbulence. This translates into a bimodality of the expected diffuse radio and gamma-ray emission of clusters, since more centrally concentrated CR will find higher target densities for hadronic CR proton interactions, higher plasma wave energy densities for CR electron and proton re-acceleration, and stronger magnetic fields. Thus, the observed bimodality of cluster radio halos appears to be a natural consequence of the interplay of CR transport processes, independent of the model of radio halo formation, be it hadronic interactions of CR protons or re-acceleration of low-energy CR electrons. Energy dependence of the CR propagation should lead to spectral steepening of dying radio halos. Furthermore, we show that the interplay of CR diffusion with advection implies first order CR re-acceleration in the pressure-stratified atmospheres of galaxy clusters. Finally, we argue that CR streaming could be important in turbulent cool cores of galaxy clusters since it heats preferentially the central gas with highest cooling rate.

show abstract

“…Montmerle 2010) raised the questions about the origin of the CR flux that generates such a high ionisation rate and how to reconcile these values with those ones measured in denser clouds that are more than one order of magnitude lower. A number of studies approached this problem using different strategies, analysing the effects of Alfvén waves on CR streaming (Skilling & Strong 1976;Hartquist et al 1978;Padoan & Scalo 2005;Rimmer et al 2012), magnetic mirroring and focusing (Cesarsky & Völk 1978;Chandran 2000;Padovani & Galli 2011), or the possible existence of a low-energy flux of CR particles able to ionise diffuse but not dense clouds (Takayanagi 1973;Umebayashi & Nakano 1981;McCall et al 2003;Padovani et al 2009). …”

Section: Introductionmentioning

confidence: 99%

Cosmic-ray ionisation in collapsing clouds

Padovani

Hennebelle

Galli

2013

A&A

103

118

View full text Add to dashboard Cite

Context. Cosmic rays play an important role in dense molecular cores, affecting their thermal and dynamical evolution and initiating the chemistry. Several studies have shown that the formation of protostellar discs in collapsing clouds is severely hampered by the braking torque exerted by the entrained magnetic field on the infalling gas, as long as the field remains frozen to the gas. Aims. In this paper we examine the possibility that the concentration and twisting of the field lines in the inner region of collapse can produce a significant reduction of the ionisation fraction. Methods. To check whether the cosmic-ray ionisation rate can fall below the critical value required to maintain good coupling, we first study the propagation of cosmic rays in a model of a static magnetised cloud varying the relative strength of the toroidal/poloidal components and the mass-to-flux ratio. We then follow the path of cosmic rays using realistic magnetic field configurations generated by numerical simulations of a rotating collapsing core with different initial conditions. Results. We find that an increment of the toroidal component of the magnetic field, or, in general, a more twisted configuration of the field lines, results in a decrease in the cosmic-ray flux. This is mainly due to the magnetic mirroring effect that is stronger where larger variations in the field direction are present. In particular, we find a decrease of the cosmic-ray ionisation rate below 10 −18 s −1 in the central 300-400 AU, where density is higher than about 10 9 cm −3 . This very low value of the ionisation rate is attained in the cases of intermediate and low magnetisation (mass-to-flux ratio λ = 5 and 17, respectively) and for toroidal fields larger than about 40% of the total field. Conclusions. Magnetic field effects can significantly reduce the ionisation fraction in collapsing clouds. We provide a handy fitting formula to compute approximately the attenuation of the cosmic-ray ionisation rate in a molecular cloud as a function of the density and the magnetic configuration.

show abstract

Régions Ioniséesémission Radio Des Régions H Ii

Cited by 57 publications

References 0 publications

Observing a column-dependentζin dense interstellar sources: the case of the Horsehead nebula

Observing a column-dependentζin dense interstellar sources: the case of the Horsehead nebula

Cosmic ray transport in galaxy clusters: implications for radio halos, gamma-ray signatures, and cool core heating

Cosmic-ray ionisation in collapsing clouds

Contact Info

Product

Resources

About