The browser you are using is not supported by this website. All versions of Internet Explorer are no longer supported, either by us or Microsoft (read more here:

Please use a modern browser to fully experience our website, such as the newest versions of Edge, Chrome, Firefox or Safari etc.

Oscar Agertz. Profile photo.

Oscar Agertz

Associate Professor / Senior university lecturer / Wallenberg Academy Fellow

Oscar Agertz. Profile photo.

The source of ionization along the magellanic stream


  • Joss Bland-Hawthorn
  • Ralph Sutherland
  • Oscar Agertz
  • Ben Moore

Summary, in English

Since its discovery in 1996, the source of the bright Ha emission (up to 750 mR) along the Magellanic Stream has remained a mystery. There is no evidence of ionizing stars within the H I stream, and the extended hot halo is far too tenuous to drive strong shocks into the clouds. We now present a hydrodynamical model that explains the known properties of the Ha emission and provides new insights on the lifetime of the Stream clouds. The upstream clouds are gradually disrupted due to their interaction with the hot halo gas. The clouds that follow plow into gas ablated from the upstream clouds, leading to shock ionization at the leading edges of the downstream clouds. Since the following clouds also experience ablation, and weaker Ha (100-200 mR) is quite extensive, a disruptive cascade must be operating along much of the Stream. In our model, the clouds are evolving on timescales of 100-200 Myr, such that the Stream must be replenished by the Magellanic Clouds at a fairly constant rate. The ablated material falls onto the Galaxy as a warm drizzle, which suggests that diffuse ionized gas at 104 K may be an important constituent of galactic accretion. The observed Ha emission provides a new constraint on the rate of disruption of the Stream and, consequently, the infall rate of metal-poor gas onto the Galaxy. When the ionized component of the Stream is fully accounted for, the rate of gas accretion is 0.4 Modot; yr-1, roughly twice the rate deduced from H i observations alone.

Publishing year





Astrophysical Journal




2 PART 2

Document type

Journal article


American Astronomical Society


  • Astronomy, Astrophysics and Cosmology


  • Galaxies: evolution
  • Galaxies: interactions
  • Hydrodynamics
  • Instabilities
  • Magellanic Clouds
  • Shock waves




  • ISSN: 0004-637X