2008/12/08 by Joshua J. Adams, Joshua J Adams, Gary J. Hill +1
Physics and Astronomy · #Astronomy #Astronomy and Astrophysical Research #Astrophysics #Galaxies: Formation, Evolution, Phenomena #Galaxy #Halo #Physics #Population #RADIUS #Radio Astronomy Observations and Technology #Redshift #Virial theorem #astro-ph
paper · pdf · doi:10.1088/0004-637x/694/1/314
published as Astrophys.J.694:314-326,2009 · 30 pages, 8 figures, 4 tables, accepted in ApJ
arxiv created 2008/12/08 · openalex publication_date 2009/03/16 · arxiv updated 2014/11/18 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We have used the visible integral-field replicable unit spectrograph prototype, a new integral field spectrograph, to study the spatially and spectrally resolved Lyman-α emission line structure in the radio galaxy B2 0902+34 at z = 3.4. We observe a halo of Lyman-α emission with a velocity dispersion of ≈250 km s −1 extending to a radius of 50 kpc. A second feature is revealed in a spatially resolved region where the line profile shows blueshifted structure. This may be viewed as either H i absorption at ≈−450 km s −1 or secondary emission at ≈−900 km s −1 from the primary peak. B2 0902+34 is also the only high-redshift radio galaxy with a detection of 21 cm absorption. Our new data, in combination with the 21 cm absorption, suggest two important and unexplained discrepancies. First, nowhere in the line profiles of the Lyman-α halo is the 21 cm absorber population evident. Second, the 21 cm absorption redshift is higher than the Lyman-α emission redshift. In an effort to explain these two traits, we have undertaken the first three-dimensional Monte Carlo simulations of resonant scattering in radio galaxies. We have created a simple model with two photoionized cones embedded in a halo of neutral hydrogen. Lyman-α photons propagate from these cones through the optically thick H i halo until reaching the virial radius. Though simple, the model produces the features in the Lyman-α data and predicts the 21 cm properties. To reach agreement between this model and the data, global infall of the H i is strictly necessary. The amount of gas necessary to match the model and data is surprisingly high, ⩾10 12 M ☉ , an order of magnitude larger than the stellar mass. The collapsing structure and large gas mass lead us to interpret B2 0902+34 as a protogiant elliptical galaxy. This interpretation is a falsifiable alternative to the presence of extended H i shells ejected through feedback events such as starburst superwinds. An understanding of these gas features and a classification of this system's evolutionary state give unique observational evidence of the formation events in massive galaxies.