Star-forming rings and disks

 

Early-type galaxies are usually considered red and dead. However, some of them exhibit in their surroundings a faint disk, forming stars at low rate. It may resemble a ring (below) or a spiral disk (to the left).  These structures are usually gas-rich, with so far HI detected in them. They also show up on GALEX UV images.

Star-forming rings and disks in a nutshell


  1. • Shape: disk, ring or spiral

  2. • Surface brightness: fainter than 26 mag.arcsec-2

  3. • Number: one, surrounding the galaxy

  4. • Color: blue typically g-r = 0.4


Examples of low surface brightness star-forming structures around ETGs, from the MATLAS imaging database.