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recently , two sets of observations have allowed us to gain a better understanding of the interaction between agns and their host galaxies .
these are observations of high  velocity wide  angle winds emanating from the vicinity of the smbh , which have been detected in a large fraction of agns ; and detection of kpc  scale quasi  spherical outflows in active galaxies , with enough power and mass flow to sweep their host galaxies clear of gas .
these outflows have kinetic power equal to a few percent of the eddington luminosity of the central black hole and their momentum flow rate is approximately an order of magnitude greater than @xmath7 .    in this paper , we show how the two types of flows can be explained within the framework of agn wind feedback .
radiation pressure from an accreting smbh expels gas in form of a wind from the nucleus ( e.g. * ? ? ?
* ; * ? ? ?
* ) , which then pushes the ambient gas in the host galaxy and produces an outflow . in recent work
@xcite we have shown that large  scale energy  driven flows ( see section [ sec : outflow ] ) can indeed drive much of the interstellar gas out of a galaxy bulge on a dynamical timescale @xmath8  yr , leaving it red and dead .
the remaining mass of the bulge is then similar to the value set by the observed black  hole 
mass relation ( e.g. * ? ? ?
the observable features of such outflows  velocities , kinetic powers and mass and momentum flow rates  are consistent with observations .
therefore agn outflows appear capable of sweeping galaxies clear of gas .
radiation pressure from an agn accreting at close to its eddington limit can expel gas from the vicinity of the nucleus with a momentum rate @xmath9 as the wind on average has scattering optical depth @xmath10 and absorbs all of the radiation momentum .
this creates a mildly relativistic diffuse wind ( @xmath11 and @xmath12 , where @xmath13 is the accretion radiative efficiency * ? ? ?
* ; * ? ? ?
observations of blueshifted x  ray iron absorption lines corresponding to velocities @xmath14 reveal that the majority of quasars produce such winds .
the winds have momentum and energy rates @xmath15
it is clear that the wind has enough kinetic power to drive the observed large scale outflow , provided that it can efficiently transfer this power to the ism . in order for this to happen
, two conditions must be satified .
first , most of the sightlines from the smbh must be covered with diffuse medium .
second , the wind can not cool efficiently . as the wind hits the ism , it shocks and heats to @xmath16
k. at this temperature , the most efficient cooling process is inverse compton scattering of the photons in the agn radiation field @xcite .
the efficiency of this process drops with increasing shock radius , thus the cooling timescale increases as @xmath17 .
since the outflow velocity does not depend strongly on radius @xcite , the flow timescale only increases as @xmath18 .
therefore , there is a critical radius , @xmath19  kpc , within which the shock can be cooled efficiently , whereas outside most of its energy is retained and transferred to the outflow .
the two cases are called momentum  driven and energy  driven flows , respectively ; their salient features are shown schematically in figure [ fig : outflow ] .
an efficiently cooled shocked wind gas is compressed to high density and radiates away almost all of its original kinetic energy , retaining and communicating only its pressure , which is equal to the pre  shock ram pressure @xmath20 , to the host ism .
for an isothermal ism density distribution with velocity dispersion @xmath21 and gas fraction @xmath22 ( the ratio of gas density to background potential density ) the behaviour of the flow depends on the black hole mass @xmath23 @xcite . for @xmath24 , where @xmath25 with @xmath26 and @xmath27 , the wind momentum is too weak to drive away
the swept  up ism , and the flow stalls . for @xmath28
the wind drives the swept  up ism far from the nucleus , quenching its own gas supply and further accretion .
therefore , @xmath29 represents an approximate upper limit to the smbh mass distribution ( see * ? ? ? * for more details ) .
the calculated mass is very similar to that obtained from observations of the @xmath30 relation , despite having no free parameter .      a large  scale ( @xmath31  kpc ) outflow becomes energy driven .
it is essentially adiabatic , and has the wind energy rate , i.e. @xmath32 ( from equation [ eq : pdotedot ] ) . the hot bubble s thermal expansion makes the driving into the host ism more vigorous than in the momentum  driven case .
observed galaxy  wide molecular outflows must be energy  driven , as demonstrated directly by their kinetic energy content ( cf .
equation [ eq : pdotedot ] ) .
the adiabatic expansion of the shocked wind pushes the swept  up interstellar medium in a ` snowplow ' .
in @xcite we derive the analytic solution for the expansion of the shocked wind in a galaxy bulge with an isothermal mass distribution . with agn luminosity @xmath33 ,
all such solutions tend to an attractor @xmath34^{1/3 } \simeq 925\sigma_{200}^{2/3}(lf_{\rm c}/f_{\rm g})^{1/3}~{\rm km\ s}^{-1 } \label{ve}\ ] ] until the agn switches off when the shock is at some radius @xmath35 .
subsequently , the expansion speed decays with @xmath36 as @xmath37 in eq .
( [ ve ] ) , the current gas fraction @xmath38 may be lower than @xmath22 ( cf .
. [ msig ] ) .
the outflow persists for an order of magnitude longer than the duration of the quasar outburst that is driving it , and reaches radii of @xmath39  pc .
it is evident that energy 
driven outflows are capable of sweeping gas out of galaxies , quenching further star formation and establishing the smbh  bulge mass relationship @xcite .
the solutions ( [ ve ] , [ dotr ] ) describe the motion of the contact discontinuity see figure [ fig : outflow ] ) .
outflows are usually observed in molecular gas , which is embedded in the outflowing shell ( see * ? ? ? * for more details ) , which moves with velocity @xmath40 from adiabatic shock conditions , using @xmath41 , and the mass outflow rate is @xmath42 assuming @xmath43 . if the agn luminosity is still close to eddington and @xmath44 , the mass loading factor ( @xmath45 ) and mass outflow rates are @xmath46 if the central quasar is no longer active , @xmath47 is lower by @xmath48 , with @xmath49 given by eq .
( [ dotr ] ) .
one can show from equations ( [ vout ] ) and ( [ eq : flmout ] ) that @xmath50 , i.e. most of the wind kinetic energy is transferred to the outflow , as expected for energy driving ( more precisely , while the quasar is active , the outflow contains @xmath51rds of the total energy ) .
we can also derive an expression for the momentum flow rate @xmath52 in the outflow : @xmath53    [ cols="^,^,^,^,^,^,^,^,^",options="header " , ]     first two columns : observed mass flow rate ( in @xmath54  yr@xmath5 ) and velocity ( in km s@xmath5 ) of large  scale outflows in molecular ( mrk231 , iras 08572 + 3915 and iras 131205453 ) and warm ionised gas ( mrk1157 ) .
middle three columns : quantities derived from observations .
last three columns : mass flow rate , velocity and mass loading factor derived from our equations ( [ vout ] ) and ( [ eq : flmout ] ) . all derived quantities show good agreement with those observed and with each other .    references : @xmath55 - @xcite ; @xmath56 - ; @xmath57 - @xcite .    [ table : obs ]
we see that in principle , large 
scale wide  angle outflows driven by a mildly relativistic wind launched by the agn radiation pressure can sweep galaxies clear of gas .
the observable properties of such outflows are typical velocities @xmath58  kms@xmath5 and mass flow rates up to @xmath59 ( equations ( [ vout ] ) and([eq : flmout ] ) ) .
the outflows should have mechanical luminosities @xmath60 , but ( scalar ) momentum rates @xmath61 , consistent with observations ( see table [ table : obs ] ) .
such outflows leave several observable signatures .
cold gas clumps entrained within the shell produce the observed molecular emission .
the inner wind shock accelerates cosmic ray particles , which can emit synchrotron radiation in the radio band and produce gamma rays when interacting with the ism .
these signatures resemble those of the gamma  ray emitting bubbles in our galaxy recently discovered by _ fermi _
@xcite , which can be explained as relics of a short quasar outburst about 6  myr ago ( * ? ? ?
* also the contribution by zubovas to this volume ) .
during the last decade , wide  angle powerful outflows from agn , both on parsec and kpc scales , have been detected in many galaxies . 
 these outflows are widely suspected to be responsible for sweeping galaxies clear of their gas . 
 we present the analytical model describing the propagation of such outflows and calculate their observable properties . 
 large  
 scale agn  
 driven outflows should have kinetic luminosities @xmath0 and momentum rates @xmath1 , where @xmath2 is the eddington luminosity of the central black hole and @xmath3 its radiative accretion efficiency . 
 this creates an expanding two  phase medium in which molecular species coexist with hot gas , which can persist after the central agn has switched off . 
 this picture predicts outflow velocities @xmath4  kms@xmath5 and mass outflow rates up to @xmath6 on kpc scales , fixed mainly by the host galaxy velocity dispersion ( or equivalently black hole mass ) . 
 we compare our prediction with recent observational data , finding excellent agreement , and suggest future observational tests of this picture .