C. Combet

The radial structure of protostellar accretion disks : influence of jets

Context. The radial structure of accretion disks is a fundamental issue regarding star and planet formation. Many theoretical studies, focussing on different aspects such as e.g. disk emissivity or ionisation, have been conducted in the context of the standard accretion disk (SAD) model, where no jet is present. Aims. We wish to calculate the structure of young stellar object (YSO) accretion disks in an approach that takes into account the presence of the protostellar jets. The radial structure of these jet emitting disks (JED) should then be compared to that of SADs. Methods. The analytical treatment used in this work is similar to standard modelling of accretion disks but uses the parameter space of magnetised accretion-ejection structures that include the jet torque on the underlying disk. In this framework, the analytical expressions of key quantities are derived, such as mid-plane temperatures, surface densities or disk aspect ratios. Results. We find that JEDs present a structure different from the SADs, which can be observationally tested. The implications on planet formation in the inner regions of accretion disks are briefly discussed. We also supply sets of analytical formulae, valid in different opacity regimes, for the disk quantities. These expressions can be readily used for any work where the disk structure is needed as an input for the model.

Disentangling cosmic-ray and dark-matter induced γ-rays in galaxy clusters

Context. Galaxy clusters are among the best targets for indirect dark matter detection in γ-rays, despite the large astrophysical background expected from these objects. Detection is now within reach of current observatories (Fermi-LAT or Cerenkov telescopes); however, assessing the origin of this signal might be difficult. Aims. We investigate whether the behaviour of the number of objects per “flux” bin (log N − log F) and that of the stacked signal could be used as a signature of the dominant process at stake. Methods. We use the Clumpy code to integrate the signal from decaying or annihilating dark matter and from cosmic rays along the line of sight. We assume the standard Navarro-Frenk-White (NFW) profile for the dark matter density and rely on a parametrised emissivity for the cosmic-ray component. In this context, the consequences of stacking are explored using the MCXC meta-catalogue of galaxy clusters. Results. We find the value of the slope of the log N − log F power law (or the increase of the signal with the number of stacked objects) to be a clear diagnosis to disentangle decaying dark matter from cosmic-ray induced γ-rays. For dark matter annihilation, depending on the signal boost from the substructures, it is either similar to the cosmic-ray signal (no boost) or similar to the decay case (large boosts). The shift between the brightest object and its followers also depends on the signal origin. For annihilation, this shift and the stacked signal are poorly constrained because of the large uncertainty affecting the boost. We also underline that the angular dependence of the annihilation signal is not universal because of the substructure contribution.