Lyman-alpha blob

A Lyman-alpha blob (LAB) is a huge concentration of a gas emitting the Lyman-alpha emission line. The Lyman-alpha emission line is produced by recombination of electrons with ionized hydrogen atoms. LABs are some of the largest known individual objects in the Universe. Some of these gaseous structures are more than 400,000 light years across. So far they have only been found in the high-redshift universe because of the ultraviolet nature of the Lyman-alpha emission line. Since the Earth's atmosphere is very effective at filtering out UV photons, the Lyman-alpha photons must be redshifted in order to be transmitted through the atmosphere.

The most famous Lyman-alpha Blobs were discovered in 2000 by Steidel "et al."Steidel "et al." 2000, "Astrophysical J.", 532, 170–182.] Matsuda "et al.", using the Subaru Telescope of the National Astronomical Observatory of Japan extended the search for LABs [ [http://www.subarutelescope.org/Pressrelease/2006/07/26/index.html Subaru Telescope, National Astronomical Observatory of Japan press release] ] and found over 30 new LABs in the original field of Steidel "et al.", although they were all smaller than the originals. These LABs form a structure which is more than 200 million light-years in extent. It is currently unknown whether LABs trace overdensities of galaxies in the high-redshift universe (as high redshift radio galaxies — which also have extended Lyman-alpha halos — do, for example), nor which mechanism produces the Lyman-alpha emission line, or how the LABs are connected to the surrounding galaxies. Lyman-alpha Blobs may hold valuable clues for scientists to determine how galaxies are formed.

The most massive Lyman-alpha blobs have been discovered by Steidel "et al." (2000), Francis "et al." (2001),Francis "et al.," 2001, "ApJ", 554, 1001.] Matsuda "et al." (2004),Matsuda "et al.", 2004, "AJ", 128, 569.] Dey "et al." (2005),Dey "et al.", 2005, "ApJ", 629, 654.] Nilsson "et al." (2006),Nilsson "et al.", 2006, "A&A", 452, 23.] and Smith & Jarvis "et al." (2007)Smith "et al.", 2007, MNRAS, 378, 49.]

ee also

* Lyman-alpha forest

References