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2008MNRAS.390.1505H - Mon. Not. R. Astron. Soc., 390, 1505-1516 (2008/November-2)
Spatially extended absorption around the z = 2.63 radio galaxy MRC 2025-218: outflow or infall?
HUMPHREY A., VILLAR-MARTIN M., SANCHEZ S.F., DI SEREGO ALIGHIERI S., DE BREUCK C., BINETTE L., TADHUNTER C., VERNET J., FOSBURY R. and STASIELAK J.
Abstract (from CDS):
Lyα absorption is detected across ∼40 x30kpc2, has a covering factor of ∼1, and shows remarkably little variation in its properties across its entire spatial extent. This absorber is kinematically detached from the extended emission line region (EELR). Its properties suggest that the absorber is outside of the EELR. We derive lower limits to the Hi, Hii and H column densities for this absorber of 3x1016,7x1017 and 2x1018/cm2, respectively. Moreover, the relatively bright emission from the active nucleus has allowed us to measure a number of metal absorption lines: Ci, Cii, Civ, Nv, Oi, Siii, Siiv, Alii and Aliii. The column density ratios are most naturally explained using photoionization by a hard continuum, with an ionization parameter U ∼ 0.0005-0.005. Shocks or photoionization by young stars cannot reproduce satisfactorily the measured column ratios. Using the ratio between the Siii* and Siii column densities, we derive a lower limit of ≥10/cm3 for the electron density of the absorber. The data do not allow useful constraints to be placed on the metallicity of the absorber.
We consider two possibilities for the nature of this absorber: the cosmological infall of gas, and an outflow driven by supernovae or the radio jets. We find it plausible that the absorber around 2025-218 is in outflow. We also find good agreement between the observed properties of the Hi absorber and the properties of the Hi absorption expected from the cosmological infall model of Barkana & Loeb.
Abstract Copyright: © 2008 The Authors. Journal compilation © 2008 RAS
Journal keyword(s): galaxies: active - galaxies: evolution - galaxies: individual: MRC 2025-218
Simbad objects: 3
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