In recent years, this type of feedback from
accreting black holes has become a key element in modeling galaxy evolution. Feedback can, in principle, explain galaxy/black
hole correlations and the lack of overly
massive blue galaxies in the local universe.
As significant as these achievements are, it
has been challenging to find direct observational evidence of black hole/galaxy selfregulation and to obtain measurements of
feedback energetics.
Quasar Winds
Quasars are so luminous (L=1045 -1047 erg/s)
that they should be able to launch powerful winds just by exerting radiation pressure
on the surrounding gas. The gas near the
quasar may be accelerated to thousands of
kilometers per second (km/s); it then pushes
on the gas further out, which in turn pushes on the gas at even larger distances from
the quasar –– thus launching a large-scale
(galaxy-wide) wind. Over the last few years,
we and our collaborators have studied the
distribution and kinematics of warm ionized
gas around quasars to search for such winds.
Figure 1.
Since the 1980s, several other groups have
independently conducted similar types of
observations. One of the most striking conclusions of these previous studies is that
quasars with relativistic jets (and those without them) showed very different morphologies of ionized gas on galaxy-wide scales.
Quasars without radio jets often showed no
detectable extended emission at all. Objects
with jets, both at low and high redshifts, routinely showed ionized gas emission on the
scale of tens of kiloparsecs (kpc), with velocities of several hundred km/s – often well in
excess of the escape velocity from the galaxy – and with high levels of turbulence.
Sometimes these outflows align nicely with
the direction of the radio jet; sometimes, the
extended ionized gas is oriented in a completely different direction. Some outflows,
especially those observed in high-redshift
radio galaxies, entrain a significant fraction
of the entire galaxy’s gas content. Thus, clear
evidence exists that powerful radio jets exert
a strong feedback effect on their hosts. The
jet heads slam into the interstellar medium
and drive shocks which engulf and accelerate at least some of the gas in the galaxy.
However, only a small fraction (~10 percent)
of accreting black holes produce powerful
jets at any given time — perhaps only some
black holes are capable of launching them,
or all black holes have them but for only a
small fraction of their active lifetime. In either case, jet-driven feedback alone is probably insufficient to make the kind of impact
necessary for establishing black hole/galaxy
correlations and for limiting galaxy mass.
Therefore, we decided to revisit observations of ionized gas around quasars without
jets (so-called “radio-quiet” quasars) to see
whether accreting black holes launch winds
in their most common phase of activity.
In order to study this we made two key
changes compared to the previous studies.
Brightness
distribution of [O iii]
emission in radioquiet quasar nebulae
on a logarithmic
scale, as measured
from our GMOS
observations (in units
of 10−17 erg s−1cm−2
arcsec−2).
10
GeminiFocus
December2012