VISION - Vienna Survey in Orion II. Infrared extinction in Orion A

Abstract

We have investigated the shape of the extinction curve in the infrared up to ~25 μm for the Orion A star-forming complex. The basis of this work is near-infrared data acquired with VISTA, in combination with Pan-STARRS and mid-infrared Spitzer photometry. We obtain colour excess ratios for eight passbands by fitting a series of colour-colour diagrams. The fits are performed using Markov chain Monte Carlo methods, together with a linear model under a Bayesian formalism. The resulting colour excess ratios are directly interpreted as a measure of the extinction law. We show that the Orion A molecular cloud is characterized by flat mid-infrared extinction, similar to many other recently studied sightlines. Moreover, we find statistically significant evidence that the extinction law from ~1 μm to at least ~6 μm varies across the cloud. In particular, we find a gradient along galactic longitude, where regions near the ONC show a different extinction law compared to L1641 and L1647, the low-mass star-forming sites in the cloud complex. These variations are of the order of only 3% and are most likely caused by the influence of the massive stars on their surrounding medium. While the observed general trends in our measurements are in agreement with model predictions, both well-established and new dust grain models are not able to fully reproduce our infrared extinction curve. We also present a new extinction map featuring a resolution of 1 arcmin and revisit the correlation between extinction and dust optical depth. This analysis shows that cloud substructure, which is not sampled by background sources, affects the conversion factor between these two measures. In conclusion, we argue that specific characteristics of the infrared extinction law are still not well understood, but Orion A can serve as an unbiased template for future studies.

accepted by Astronomy & Astrophysics

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• VISION - Vienna survey in Orion. III. Young stellar objects in Orion A
• Ruprecht 147: a paradigm of dissolving star cluster
• The $\rho$ Oph region revisited with Gaia EDR3
• Galactic extinction laws: I. A global NIR analysis with 2MASS photometry
• Spatial field reconstruction with INLA: Application to IFU galaxy data
• ALMA Survey of Orion Planck Galactic Cold Clumps (ALMASOP): How do dense core properties affect the multiplicity of protostars?
• VISIONS: The VISTA Star Formation Atlas -- I. Survey overview
• Dust extinction map of the Galactic plane based on the VVV survey data
• The CARMA-NRO Orion Survey: Core Emergence and Kinematics in the Orion A Cloud
• Optimal extinction measurements - I. Single-object extinction inference
• Optical Properties of Interstellar Dust around the Orion A Molecular Cloud
• Systematic Investigation of Dust and Gaseous CO in 12 Nearby Molecular Clouds