Bibcode
Hall, P. B.; Brandt, W. N.; Petitjean, P.; Pâris, I.; Filiz Ak, N.; Shen, Yue; Gibson, R. R.; Aubourg, É.; Anderson, S. F.; Schneider, D. P.; Bizyaev, D.; Brinkmann, J.; Malanushenko, E.; Malanushenko, V.; Myers, A. D.; Oravetz, D. J.; Ross, N. P.; Shelden, A.; Simmons, A. E.; Streblyanska, A.; Weaver, B. A.; York, D. G.
Bibliographical reference
Monthly Notices of the Royal Astronomical Society, Volume 434, Issue 1, p.222-256
Advertised on:
9
2013
Citations
39
Refereed citations
37
Description
We report the discovery in the Sloan Digital Sky Survey (SDSS) and the
SDSS-III Baryon Oscillation Spectroscopic Survey of 17 broad absorption
line (BAL) quasars with high-ionization troughs that include absorption
redshifted relative to the quasar rest frame. The redshifted troughs
extend to velocities up to v ≃ 12 000 km s-1 and the
trough widths exceed 3000 km s-1 in all but one case.
Approximately 1 in 1000 BAL quasars with blueshifted C IV absorption
also has redshifted C IV absorption; objects with C IV absorption
present only at redshifted velocities are roughly four times rarer. In
more than half of our objects, redshifted absorption is seen in C II or
Al III as well as C IV, making low-ionization absorption at least 10
times more common among BAL quasars with redshifted troughs than among
standard BAL quasars. However, the C IV absorption equivalent widths in
our objects are on average smaller than those of standard BAL quasars
with low-ionization absorption.
We consider several possible ways of generating redshifted absorption.
The two most likely possibilities may be at work simultaneously, in the
same objects or in different ones. Rotationally dominated outflows seen
against a quasar's extended continuum source can produce redshifted and
blueshifted absorption, but variability consistent with this scenario is
seen in only one of the four objects with multiple spectra. The infall
of relatively dense and low-ionization gas to radii as small as 400
Schwarzschild radii can in principle explain the observed range of
trough profiles, but current models do not easily explain the origin and
survival of such gas. Whatever the origin(s) of the absorbing gas in
these objects, it must be located at small radii to explain its large
redshifted velocities, and thus offers a novel probe of the inner
regions of quasars.
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This IAC research group carries out several extragalactic projects in different spectral ranges, using space as well as ground-based telescopes, to study the cosmological evolution of galaxies and the origin of nuclear activity in active galaxies. The group is a member of the international consortium which built the SPIRE instrument for the
Ismael
Pérez Fournon