On the scarcity of Magellanic Cloud-like satellites

TL;DR

This study uses H alpha imaging to investigate the frequency and properties of star-forming satellite galaxies around luminous spirals, revealing that Magellanic Cloud-like satellites are rare and the Milky Way's satellites are unusual.

Contribution

It provides the first large survey quantifying the scarcity of Magellanic Cloud-like satellites around similar galaxies.

Findings

Star-forming satellites are rare, with two-thirds of galaxies having none.

The median luminosity difference between central galaxies and satellites is 4.6 mag.

Close satellite pairs like the Magellanic Clouds are extremely uncommon.

Abstract

We have used H alpha narrow-band imaging to search for star-forming satellite galaxies around 143 luminous spiral galaxies, with the goal of quantifying the frequency of occurrence of satellites resembling the Magellanic Clouds, around galaxies comparable to the Milky Way. For two-thirds of the central galaxies, no star-forming satellites are found, down to luminosities and star-formation rates well below those of the Magellanic Clouds. A total of 62 satellites is found, associated with 47 of the central galaxies searched. The R-band magnitude difference between central galaxies and their satellites has a median value of 4.6 mag, and a maximum of 10.2 mag. The mean projected separation of the satellites from their central galaxies is 81 kpc, or 98 kpc for systems beyond 30 Mpc. Thus star-forming satellites are quite rare, and the Milky Way is unusual both for the luminosity and the proximity of its two brightest satellites. We also find that the Clouds themselves are unusual in that they appear to form a bound binary pair; such close satellite pairs, of any luminosity, are also extremely rare in our survey.