Dust in a compact, cold, high-velocity cloud: A new approach to removing foreground emission

TL;DR

This study introduces a novel foreground removal method using a regularised linear model and Bayesian fitting to detect dust in a high-velocity cloud, but finds no significant dust emission, setting new upper limits.

Contribution

The paper presents a new approach combining regularised linear modeling and Bayesian fitting for foreground removal in dust detection within high-velocity clouds.

Findings

Foreground dust emission can be modeled accurately with the proposed method.

No significant dust emission detected in the studied HVC.

Upper limit to dust emissivity is an order of magnitude below typical Galactic values.

Abstract

Because isolated high-velocity clouds (HVCs) are found at great distances from the Galactic radiation field and because they have subsolar metallicities, there have been no detections of dust in these structures. A key problem in this search is the removal of foreground dust emission. Using the Effelsberg-Bonn HI Survey and the Planck far-infrared data, we investigate a bright, cold, and clumpy HVC. This cloud apparently undergoes an interaction with the ambient medium and thus has great potential to form dust. To remove the local foreground dust emission we used a regularised, generalised linear model and we show the advantages of this approach with respect to other methods. To estimate the dust emissivity of the HVC, we set up a simple Bayesian model with mildly informative priors to perform the line fit instead of an ordinary linear least-squares approach. We find that the foreground can be modelled accurately and robustly with our approach and is limited mostly by the cosmic infrared background. Despite this improvement, we did not detect any significant dust emission from this promising HVC. The 3-sigma upper limit to the dust emissivity is an order of magnitude below the typical values for the Galactic interstellar medium.