Spatially extended absorption around the z = 2.63 radio galaxy MRC 2025-218: outflow or infall?
Humphrey, A.; Villar-Martín, M.; Sánchez, S. F.;di Serego Alighieri, S.; De Breuck, C.; Binette, L.;Tadhunter, C.; Vernet, J.; Fosbury, R.;Stasielak, J.. Spatially extended absorption around the z = 2.63 radio galaxy MRC 2025-218: outflow or infall?. Monthly Notices of the Royal Astronomical Society. 2008, Vol. Volume 390, Issue 4, pp. 1505-1516., p. -2008.
We present an investigation into the absorber in front of the z = 2.63
radio galaxy MRC 2025-218, using integral field spectroscopy obtained at
the Very Large Telescope, and long-slit spectroscopy obtained at the
Keck II telescope. The properties of MRC 2025-218 are particularly
conducive to study the nature of the absorbing gas, i.e. this galaxy
shows bright and spatially extended Lyα emission, along with
bright continuum emission from the active nucleus.
Lyα absorption is detected across ~40 × 30kpc<SUP>2</SUP>,
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 3 × 10<SUP>16</SUP>,7 × 10<SUP>17</SUP> and 2
× 10<SUP>18</SUP>cm<SUP>-2</SUP>, 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 >=10cm<SUP>-3</SUP> 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.
We present an investigation into the absorber in front of the z = 2.63
radio galaxy MRC 2025-218, using integral field spectroscopy obtained at
the Very Large Telescope, and long-slit spectroscopy obtained at the
Keck II telescope. The properties of MRC 2025-218 are particularly
conducive to study the nature of the absorbing gas, i.e. this galaxy
shows bright and spatially extended Lyα emission, along with
bright continuum emission from the active nucleus.
Lyα absorption is detected across ~40 × 30kpc<SUP>2</SUP>,
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 3 × 10<SUP>16</SUP>,7 × 10<SUP>17</SUP> and 2
× 10<SUP>18</SUP>cm<SUP>-2</SUP>, 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 >=10cm<SUP>-3</SUP> 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.