The Distance and Properties of Hydrogen Clouds in the Leading Arm of the Magellanic System

TL;DR

This study uses high-resolution radio observations to analyze the structure, properties, and potential distance variations of hydrogen clouds in the Magellanic Leading Arm, revealing insights into their origin and evolution.

Contribution

It provides the first observational evidence of varying distances within the Leading Arm region using combined high-resolution and single-dish data.

Findings

Detected a gradient in physical properties along the Leading Arm

Identified cold, compact clumps with narrow linewidths

Suggested the leading part of the Leading Arm is closer to the Galactic disc

Abstract

We present a high-resolution study of five high-velocity clouds in the Magellanic Leading Arm region. This is a follow-up study of our widefield Parkes survey of the region in order to probe the multiphase structures of the clouds and to give an insight to their origin, evolution and distance. High-resolution data were obtained from the Australia Telescope Compact Array. By combining with single-dish data from the Galactic All-Sky Survey (GASS), we are able to probe compact and diffuse emission simultaneously. We identify resolved and unresolved clumps. Physical parameters were derived for both diffuse structure and compact clumps. The latter are cold with typical velocity linewidths of 5 km/s. We find a gradient in thermal halo pressure, hydrogen density and HI column density of HVC as a function of Galactic latitude. This is possibly the first observational evidence of varying distance in the Leading Arm region, with the leading part of the Leading Arm (LA II and III) probably being closer to the Galactic disc than the trailing end (LA I).