2006/12/05 by M. Villar-Martin, M. Villar‐Martín, A. Humphrey +5 · 69 citations
Physics and Astronomy · #Astronomy #Astrophysics #Astrophysics and Cosmic Phenomena #Astrophysics and Star Formation Studies #Galaxies: Formation, Evolution, Phenomena #Galaxy #Galaxy formation and evolution #Ionization #Photoionization #Physics #Population #Radio galaxy #Redshift #Star formation #astro-ph
paper · pdf · doi:10.1111/j.1365-2966.2006.11371.x
published in Monthly Notices of the Royal Astronomical Society 375(4), 1299-1310 (Oxford University Press) · 14 pages, 5 figures, accepted for publication in MNRAS
arxiv created 2006/12/05 · openalex publication_date 2007/02/03 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/08
About 54% of radio galaxies at z>3 and 8% of radio galaxies at 2<z<3 show unusually strong Ly-alpha emission, compared with the general population of high redshift (z>2) radio galaxies. These Ly-alpha excess objects (LAEs) show Ly-alpha/HeII values consistent with or above standard photoionization model predictions. We show that the most successful explanation is the presence of a young stellar population which provides the extra supply of ionizing photons required to explain the Ly-alpha excess in at least the most extreme LAEs (probably in all of them). The measurement of unusually high Ly-alpha ratios in the extended gas of some high redshift radio galaxies suggests that star formation activity occurs in spatial scales of tens of kpc. We argue that, although the fraction of LAEs may be incompletely determined, both at 2<z<3 and at z>3, the much larger fraction of LAEs found at z>3 is a genuine redshift evolution and not due to selection effects. Therefore, our results suggest that the radio galaxy phenomenon is more often associated with a massive starburst at z>3 than at z<3.