Galaxies are social beasts that are mostly found in groups or
clusters – large assemblies of galaxies that are permeated by even
larger amounts of diffuse gas. With temperatures of 10 million degrees
or more, the gas in galaxy groups and clusters is hot enough to shine
brightly in X-rays and be detected by ESA’s XMM-Newton X-ray
observatory.
As galaxies speed through these gigantic cauldrons,
they occasionally jumble the gas and forge it into lop-sided shapes. An
example is revealed in this composite image of the galaxy group NGC
5044, the brightest group in X-rays in the entire sky.
The group
is named after the massive and bright elliptical galaxy at its centre,
surrounded by tens of smaller spiral and dwarf galaxies. The galaxies
are shown in a combination of optical images from the Digitized Sky
Survey with infrared and ultraviolet images from NASA’s WISE and Galex
satellites, respectively. Foreground stars are also sprinkled across the
image.
The large blue blob shows the distribution of hot gas
filling the space between NGC 5044’s galaxies as imaged by XMM-Newton.
From the X-ray observations, astronomers can also see the glow of iron
atoms that were forged in stellar explosions within the galaxies of the
group but streamed beyond. The distribution of iron atoms is shown in
purple.
Embedded within the hot gas are clouds of even more
energetic plasma that emit radio waves – a reminder of the past activity
of a supermassive black hole lurking at the centre of the group. These
are the green filament extending from the central galaxy to the lower
right and the larger green region to its lower left, which were imaged
with the Giant Metrewave Radio Telescope, near Pune in India.
The
distribution of the intergalactic gas and its ingredients is asymmetric,
with a larger splotch in the upper right part of the image and a
smaller one in the lower left.
Astronomers believe that gas in NGC
5044 is sloshing as a consequence of a galaxy that passed through it
several millions of years ago. The culprit is the spiral galaxy NGC
5054, which is not visible here, instead hiding beyond its lower left
corner.
The transit of NGC 5054 through the centre of the group may have also caused the twisted shape of the radio-bright filament.
This image was first published in the XMM-Newton Image Gallery in October 2013. The analysis is reported in the paper by E. O’Sullivan et al. “The impact of sloshing on the intra-group medium and old radio lobe of NGC 5044.”
Source: ESA
