Chandra observations of merging galaxies

The following images show brand-new Chandra X-ray images, together with grey-scale optical images for a number of interacting galaxies. The Chandra images are colour-coded, such that red represents soft (cool) X-ray emission [0.2-0.9 keV], green intermediate [0.9-2.5 keV] and blue hard (hot) X-ray emission [2.5-10 keV].

[Arp270: Chandra] [Arp270: Optical]

The two images shown above of the early merger Arp 270 (where the galaxy disks are still very distinct) are of approximately equal size. Cool (less than 1 million degree) diffuse gaseous emission is seen associated with the two galaxy disks and several point sources of varying hardness (temperature) are seen scattered within the galaxies. Of great and novel interest are the hard point sources seen where the disks collide. A new idea that is being considered is that they may be due to strong star-formation as the two gaseous disks rotate through each other.

[The Mice: Chandra] [The Mice: Optical]

The Mice (Arp 242), so-called because of their distinctive tails, are shown above. The X-ray image is taken from an area far smaller than the optical image, such that the two main X-ray features are from the two galaxy nuclei. The southern nucleus appears harder in X-rays than the northern, and further emission is seen from within the northern tail. The northern galaxy also shows what appears to be a small bipolar X-ray outflow - a great rarity in such a violently evolving classic merger system.

[Mkn266: Chandra] [Mkn266: Optical]

Mkn 266 above consists of two galaxies about to merge (the two nuclei can just be distinguished in the optical image). The Chandra image resolves the two nuclei, with the northern nucleus appearing significantly harder. Interestingly, very soft, diffuse gaseous emission is seen to the north and to the east of the system - thought to be due to a stronger and more evolved and distorted outflow than the type seen in e.g. the Mice.

Further X-ray and optical images of merging (and other) galaxies can be found here.
This page was written by Andy Read, and last updated on