ESO Chile Image of the Month - April 2008 A composite infrared image of the X-ray luminous galaxy cluster XMMU J2235.3-2557 at redshift 1.4, one of the most distant galaxy clusters known.
The composite is made of 4 HAWK-I pointings in both J and Ks and covers 13.5 arc minutes on a side. The cluster is right in the middle of the frame and is difficult to see, given the large field of view, so a blow-up centred on the cluster is shown in the inset. As can be seen by eye, the core of the cluster is dominated by red galaxies with very similar colours. The stars in these galaxies are already very old. On average they formed when the Universe was only one billion years old. As one moves away from the center of the cluster, cluster galaxies become slightly bluer, suggesting that galaxies in the outskirts are either younger or have recently experienced a small amount of star formation (commonly called "frosting"). As one moves even further out, the authors hope to find small groups of galaxies that will, one day, merge with the core.
In the standard flat, lambda-dominated cosmology, the universe is 4.6 billion years old at redshift 1.4 and 1.1 billion years old at redshift 5. The universe at redshift 0 (today) is 13.7 billion years old.
At a redshift of 1.4, 10 arc minutes on the sky corresponds to a linear distance of 5 Mpc (15,000,000,000,000,000,000 km).
The composite is made of 4 HAWK-I pointings in both J and Ks and covers 13.5 arc minutes on a side. The cluster is right in the middle of the frame and is difficult to see, given the large field of view, so a blow-up centred on the cluster is shown in the inset. As can be seen by eye, the core of the cluster is dominated by red galaxies with very similar colours. The stars in these galaxies are already very old. On average they formed when the Universe was only one billion years old. As one moves away from the center of the cluster, cluster galaxies become slightly bluer, suggesting that galaxies in the outskirts are either younger or have recently experienced a small amount of star formation (commonly called "frosting"). As one moves even further out, the authors hope to find small groups of galaxies that will, one day, merge with the core.
In the standard flat, lambda-dominated cosmology, the universe is 4.6 billion years old at redshift 1.4 and 1.1 billion years old at redshift 5. The universe at redshift 0 (today) is 13.7 billion years old.
At a redshift of 1.4, 10 arc minutes on the sky corresponds to a linear distance of 5 Mpc (15,000,000,000,000,000,000 km).
Authors: Chris Lidman, Piero Rosati,
Masyuki Tanaka and the HAWK-I science verification team.
ESO - European Organisation
for Astronomical Research in theSouthern Hemisphere
Masyuki Tanaka and the HAWK-I science verification team.
ESO - European Organisation
for Astronomical Research in theSouthern Hemisphere
