Extinction and dust properties in a clumpy medium

Abstract

(abridged) The dust content of the universe is primarily explored via its interaction with stellar photons, producing interstellar extinction. However, owing to the physical extension of the observing beam, observations may detect scattered photons, resulting in a change in the observed (or effective) extinction, depending on the spatial distribution of the dust and the resolution of the instrument. We investigate the influence of clumpy dust distributions on effective extinction toward embedded sources and those in the diffuse ISM. We use Monte Carlo radiative transfer to examine effective extinction for various geometries. By varying the number, optical depth and volume-filling factor of clumps in models of spherical shells and the diffuse ISM, we explore the evolution of extinction. Depending on the number of scattering events in the beam, the extinction curve steepens in homogeneous media and flattens in clumpy media. As a result, clumpy dust distributions can to reproduce extinction curves with arbitrary R_v, the effective ratio of total-to-selective extinction. The flattening `washes out' the 2175 Åbump and shifts the peak to shorter wavelengths. The mean R_v of a shell correlates with the optical depth of an individual clump and the wavelength at which a clump becomes optically thick. Similar behaviour is seen for edge-on discs or tori. However, at grazing inclinations the combination of extinction and strong forward scattering results in chaotic behaviour. Caution is therefore advised when measuring extinction in, for example, AGN tori or toward SNIa or GRB afterglows. In face-on discs, the shape of the scattered continuum changes with clumpiness, however, unlike absorption features, individual features in the scattering cross-sections are preserved. Finally, we show that diffuse interstellar extinction is not modified by scattering on scales of a few kpc.

12 pages, 15 figures; A&A, accepted

References in corpus (2)

• An Analysis of the Shapes of Interstellar Extinction Curves. V. The IR-Through-UV Curve Morphology
• Dust in Active Galactic Nuclei: Anomalous Silicate to Optical Extinction Ratios?

Cited by in corpus (16)

• Characterizing the UV-to-NIR shape of the dust attenuation curve of IR luminous galaxies up to z$\sim$2
• Evolution of dust extinction curves in galaxy simulation
• Polar dust obscuration in broad-line active galaxies from the XMM-XXL field
• Investigation of dust attenuation and star formation activity in galaxies hosting GRBs
• MUSE stares into the shadows: the high-resolution dust attenuation curve of NGC 5626
• Geometry effects on dust attenuation curves with different grain sources at high redshift
• Dark Dust and single-cloud sightlines in the ISM
• Large Interstellar Polarisation Survey II. UV/optical study of cloud-to-cloud variations of dust in the diffuse ISM
• Dust evolution processes constrained by extinction curves in nearby galaxies
• Resolved imaging of the AR Puppis circumbinary disk
• Constraints on interstellar dust models from extinction and spectro-polarimetry
• Far-infrared emission of massive stars
• Optical properties and dust temperatures in clumpy diffuse medium
• Capture and Escape: The Dependence of Radiation Forces on Clumping in Dusty Envelopes
• Paradigmatic examples for testing models of optical light polarization by spheroidal dust
• Evaluating star formation rates at z = 5