A&A 601, A143 (2017)
DOI: 10.1051/0004-6361/201629478
c
ESO 2017
Astronomy
&
Astrophysics
AGN wind scaling relations and the co-evolution of black
holes and galaxies
F. Fiore
1
, C. Feruglio
2
, F. Shankar
3
, M. Bischetti
1
, A. Bongiorno
1
, M. Brusa
4, 5
, S. Carniani
6, 7
, C. Cicone
8, 9
, F. Duras
1
,
A. Lamastra
1
, V. Mainieri
10
, A. Marconi
6, 11
, N. Menci
1
, R. Maiolino
7
, E. Piconcelli
1
, G. Vietri
1
, and L. Zappacosta
1
1
INAF–Osservatorio Astronomico di Roma, via Frascati 33, 00078 Monteporzio Catone, Italy
e-mail: fabrizio.fiore@oa-roma.inaf.it
2
INAF–Osservatorio Astronomico di Trieste, via G. Tiepolo 11, 34124 Trieste, Italy
3
Department of Physics and Astronomy, University of Southampton, Highfield, SO17 1BJ, UK
4
Dipartimento di Fisica e Astronomia, Alma Mater Studiorum – Universitá di Bologna, viale Berti Pichat 6/2, 40127 Bologna, Italy
5
INAF–Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
6
Dipartimento di Fisica e Astronomia, Universitá di Firenze, via G. Sansone 1, 50019 Sesto F.no, Firenze, Italy
7
Cavendish Laboratory, University of Cambridge, 19 J. J. Thomson Ave., Cambridge CB3 0HE, UK
8
INAF–Osservatorio Astronomico di Brera, via Brera 28, 20121 Milan, Italy
9
ETH, Institute for Astronomy, Department of Physics, Wolfgang-Pauli-Strasse 278093 Zurich, Switzerland
10
European Southern Observatory, Karl-Schwarzschild-str. 2, 85748 Garching bei München, Germany
11
INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
Received 4 August 2016 / Accepted 13 February 2017
ABSTRACT
Context. Feedback from accreting supermassive black holes (SMBHs) is often identified as the main mechanism responsible for
regulating star formation in active galactic nucleus (AGN) host galaxies. However, the relationships between AGN activity, radiation,
winds, and star formation are complex and still far from being understood.
Aims. We study scaling relations between AGN properties, host galaxy properties, and AGN winds. We then evaluate the wind mean
impact on the global star formation history, taking into account the short AGN duty cycle with respect to that of star formation.
Methods. We first collect AGN wind observations for 94 AGN with detected massive winds at sub-pc to kpc spatial scales. We then
fold AGN wind scaling relations with AGN luminosity functions, to evaluate the average AGN wind mass-loading factor as a function
of cosmic time.
Results. We find strong correlations between the AGN molecular and ionised wind mass outflow rates and the AGN bolometric
luminosity. The power law scaling is steeper for ionised winds (slope 1.29 ± 0.38) than for molecular winds (0.76 ± 0.06), meaning
that the two rates converge at high bolometric luminosities. The molecular gas depletion timescale and the molecular gas fraction of
galaxies hosting powerful AGN driven winds are 3–10 times shorter and smaller than those of main sequence galaxies with similar
star formation rate (SFR), stellar mass, and redshift. These findings suggest that, at high AGN bolometric luminosity, the reduced
molecular gas fraction may be due to the destruction of molecules by the wind, leading to a larger fraction of gas in the atomic ionised
phase. The AGN wind mass-loading factor η =
˙
M
OF
/SFR is systematically higher than that of starburst driven winds.
Conclusions. Our analysis shows that AGN winds are, on average, powerful enough to clean galaxies from their molecular gas only
in massive systems at z
<
∼
2, i.e. a strong form of co-evolution between SMBHs and galaxies appears to break down for the least
massive galaxies.
Key words. galaxies: active – galaxies: evolution – quasars: general
1. Introduction
The past decades have seen a hot debate on whether, and how,
the evolution of galaxies and of the supermassive black holes
(SMBHs) hosted in their nuclei is correlated.
The debate started with the HST discovery of SMBHs in
most local bulges (Richstone et al. 1998). SMBH mass and
host bulge properties – such as velocity dispersion, luminos-
ity, and mass – were found to closely correlate with each other
(Gebhardt et al. 2000; Ferrarese & Ford 2005; Kormendy & Ho
2013, and references therein, but see also Shankar et al. 2016,
2017). Furthermore, the comparison of the SMBH mass func-
tion derived from the active galactic nucleus (AGN) luminos-
ity function and from the local bulge luminosity function sug-
gests that SMBH growth is mostly due to accretion of matter
during their active phases, and therefore that most bulge galaxies
passed a phase of strong nuclear activity (Soltan 1982; Marconi
et al. 2004; Shankar et al. 2004; Merloni & Heinz 2008). Both
findings seemed to imply links between SMBH accretion and
bulge formation, i.e. a strong form of AGN/galaxy co-evolution.
Indeed, soon after the discovery of the SMBH-bulge relation-
ships, several authors (Silk & Rees 1998; Fabian 1999; King
2003; Granato et al. 2004) suggested that they can be naturally
explained if AGN winds efficiently interact with the galaxy ISM.
When the black hole reaches a critical mass it may be powerful
enough to heat up and eject the gas from the galaxy, terminat-
ing the growth of both SMBH and galaxy, and giving rise to
the observed scaling between SMBH mass and bulge velocity
dispersion. AGN feedback not only modify AGN host galaxies
it can also affect the intra-cluster matter (ICM) in groups and
Article published by EDP Sciences A143, page 1 of 21
A&A 601, A143 (2017)
clusters of galaxies. Two modes for AGN feedback have been
indeed postulated, the so-called radio-mode in the central clus-
ter galaxies and the quasar-mode, characterised by slower winds
of both ionised, neutral atomic, and molecular matter.
Radio-mode feedback is evident in cool core clusters and
groups, where the ICM is heated up by AGN jet-driven radio
bubbles. The power to excavate cavities in the ICM is pro-
portional to the X-ray luminosity, and the power in cavities is
proportional to the AGN radio luminosity (see McNamara &
Nulsen 2007; Cattaneo et al. 2009; Fabian 2012, for reviews).
Interestingly, only the brightest central galaxies (BCGs) in clus-
ters/groups with low inner entropy (short cooling time) have an
active nucleus, and are actively forming stars (Cavagnolo et al.
2008, 2009). The situation is best described by Voit & Donahue
(2015): “a delicate feedback mechanism where AGN input en-
ergy regulates the gas entropy and in turn further gas accretion
and star formation (stars can form from low entropy, cold and
dense gas only)”. Thus, a multiphase gas structure naturally de-
velops in cluster cores and within the BCGs leading to AGN
feedback triggered by cold accretion (Gaspari et al. 2012, 2013,
2014, 2017).
Similar autoregulation may occur in galaxies other than
BCGs, where feedback might be due to more common AGN
winds. Indeed, several direct observation of ISM modifications
by AGN winds have been collected so far. Cano-Diaz et al.
(2012), Cresci et al. (2015), and Carniani et al. (2016) have
found that AGN winds and actively star-forming regions are spa-
tially anti-correlated. Similarly, Davies et al. (2007) and Lipari
et al. (2009) found little evidence for young (Myr) stellar pop-
ulations in the
<
∼
1 kpc region of Markarian 231 where a power-
ful molecular outflow is observed (Feruglio et al. 2010, 2015).
However, although promising, these quasar-mode feedback ob-
servations are still too sparse to derive strong conclusions. The
correlation between SMBHs and bulge properties do not nec-
essarily require feedback, and can be also explained if SMBHs
and bulges formed simultaneously, during episodes when a fixed
fraction of gas accretes toward the central black hole while the
rest forms the spheroid stars. Menci et al. (2003) reproduced the
BH mass – σ
bulge
correlation as the combination of three factors:
a) the merging histories of the galactic dark matter clumps, im-
plying that the mass of the available cold gas scales as σ
2.5
; b) the
destabilisation of cold gas by galaxy interactions, which steepens
the correlation by another factor σ; and c) SNe feedback, which
depletes the residual gas content of shallow potential wells, fur-
ther steepening the correlation. Later, Peng (2007) showed that
galaxy mergers are efficient in averaging out extreme values of
M
BH
/M
∗
, converging toward a narrow correlation between these
quantities, close to the observed one, even starting from arbitrary
distributions. Jahnke & Macció (2011) showed that the number
of mergers needed to this purpose is consistent with that of stan-
dard merger tree models of hierarchical galaxy (and SMBH) for-
mation. In this scenario the SMBHs and bulges do not necessar-
ily know about each other. No causal connection exists between
these systems, and their properties are connected just by natural
scaling relations. We can call this as a weak form of AGN/galaxy
co-evolution. More recently, the analysis of Shankar et al. (2016)
supports a strong dependence between SMBH mass and bulge
velocity dispersion, while the dependence with the bulge mass is
weaker, disfavouring this scenario, and suggesting to investigate
AGN/galaxy co-evolution independently from the SMBH mass
– bulge mass scaling relations.
Comparing model predictions to the observed SMBH mass –
bulge properties hardly allows one to discriminate between weak
and strong forms of AGN/galaxy co-evolution. This is probably
due to the fact that SMBH mass and bulge properties are quan-
tities integrated along cosmic time, with SMBHs and bulges as-
sembled during the Hubble time, as a consequence of several
merging and accretion events. A different route attempted to dis-
tinguish between weak and strong forms of co-evolution, is to
study derivative quantities, such as the SMBH accretion rate
and the star formation rate (SFR), or, the cosmological evolu-
tion of the AGN and galaxy luminosity densities. Franceschini
et al. (1999) were among the first to realise that the luminos-
ity dependent evolution of AGN, with lower luminosity AGN
peaking at a redshift lower than luminous QSOs (Ueda et al.
2003, 2014; Fiore et al. 2003; La Franca et al. 2005; Brandt &
Hasinger 2005; Bongiorno et al. 2007; Aird et al. 2015; Brandt
& Alexander 2015), mirrors that of star-forming galaxies and
of massive spheroids. These trends, dubbed “downsizing” by
Cowie et al. (1996), and in general the relationship between the
evolution of AGN and galaxy growth, may arise from feedback
mechanisms linking nuclear and galactic processes.
Indirect evidence for AGN feedback come from the
statistical properties of AGN host galaxies with respect to the
inactive population. It is well known since the pioneering HST
studies of Bahcall et al. (1997) that luminous QSOs reside pref-
erentially in massive, spheroid-dominated host galaxies, whereas
lower luminosity QSOs are found in both spheroidal and disky
galaxies (Dunlop et al. 2003; Jahnke et al. 2004, and references
therein). The distribution of AGN host galaxy colours, mor-
phologies, SFR, specific SFR are wider than that of star-forming
galaxies of similar masses, and skewed toward redder/more in-
active galaxies (e.g. Alexander et al. 2002; Mignoli et al. 2004;
Brusa et al. 2005, 2009, 2010; Nandra et al. 2007; Mainieri et al.
2011; Bongiorno et al. 2012; Georgakakis et al. 2014). Many
AGN are hosted in red-and-dead galaxies, or lie in the so called
green valley. Recent ALMA observations of X-ray selected AGN
in the GOODS field (Mullaney et al. 2015) confirmed these ear-
lier results, showing that the bulk of the AGN population lie be-
low the galaxy main sequence (see Daddi et al. 2007; Rodighiero
et al. 2011, and refs. therein). Because the stellar mass func-
tion of star-forming galaxies is exponentially cut-offed above a
quenching mass M
∗
∼ 10
11
M
(Peng et al. 2010), the galaxy
main sequence flattens above the same mass, whereas the star
formation efficiency and the gas-to-star mass fraction decrease
(Genzel et al. 2010, and references therein). AGN feedback may
well be one of the drivers of these transformations, as well as
the main driver for the quenching of star formation in massive
galaxies (Bongiorno et al. 2016), pointing toward a strong form
of AGN/galaxy co-evolution. We explore this possibility in this
paper.
This paper is organised as follows. In Sect. 2 we review AGN
massive wind observations, and study the scaling relationships
between wind mass outflow rate, velocity, kinetic power, mo-
mentum load, AGN bolometric luminosity and host galaxy SFR.
We then plug AGN wind studies in the broader scenario of star-
forming galaxies scaling relations (Genzel et al. 2015, and refer-
ences therein), to understand whether AGN hosting strong winds
are outliers in these relationships. We study the relationships be-
tween the depletion timescale (the ratio between molecular gas
mass and SFR), and gas fraction (the ratio between molecular
gas mass and galaxy stellar mass), with the offset from the galaxy
main sequence, redshift and host galaxy stellar mass, for a sam-
ple of sources with interferometric molecular measurements. In
Sect. 3 we evaluate the wind statistical relevance on the global
star formation history, by folding the AGN wind scaling rela-
tions with the AGN luminosity functions. This accounts for the
fact that AGN shine in a relatively small fraction of galaxies, i.e.
A143, page 2 of 21
F. Fiore et al.: AGN wind scaling relations
the AGN timescales are usually shorter than the star formation
timescales. We compare the cosmic, average AGN outflow rate,
computed by using the AGN wind scaling relations, to the galaxy
cosmic star formation rate, to study the regimes (galaxy masses,
cosmic epoch) where AGN winds are statistically strong enough
to affect star formation in the global galaxy population. Section
4 presents our conclusions. A H
0
= 70 km s
−1
Mpc
−1
, Ω
M
= 0.3,
Ω
Λ
= 0.7 cosmology is adopted throughout.
2. AGN wind scaling relations
Although wind observations are very common in AGN (see Elvis
2000; Veilleux et al. 2005; and Fabian 2012, for reviews), most
studies concern ionised gas and uncertain spatial scales. In the
past few years the situation changed drastically. Several fast (v
OF
of the order of 1000 km s
−1
), massive outflows of ionised, neutral
and molecular gas, extended on kpc scales, have been discovered
thanks to three techniques: 1) deep optical/NIR spectroscopy,
mainly from integral field observations (IFU, e.g. Nesvadba
et al. 2006, 2008; Alexander et al. 2010; Rupke & Veilleux
2011; Riffel & Storchi-Bergmann 2011; Cano-Diaz et al. 2012;
Greene et al. 2012; Harrison et al. 2012, 2014; Liu et al. 2013a,b;
Cimatti et al. 2013; Tadhunter et al. 2014; Genzel et al. 2014;
Brusa et al. 2015a; Cresci et al. 2015; Carniani et al. 2015; Perna
et al. 2015a,b; Zakamska et al. 2016); 2) interferometric obser-
vations in the (sub)millmetre domain (e.g. Feruglio et al. 2010,
2013a,b, 2015; Alatalo et al. 2011; Aalto et al. 2012; Cicone
et al. 2012, 2014, 2015; Maiolino et al. 2012, Krips et al. 2011;
Morganti et al. 2013a,b; Combes et al. 2013; Garcia-Burillo
et al. 2014); and 3) far-infrared spectroscopy from Herschel (e.g.
Fischer et al. 2010; Sturm et al. 2011; Veilleux et al. 2013; Spoon
et al. 2013; Stone et al. 2016; Gonzalez-Alfonso et al. 2017). In
addition, AGN-driven winds from the accretion disk scale up to
the dusty torus are now detected routinely both in the local and
in the distant Universe, as blue-shifted absorption lines in the
X-ray spectra of a substantial fraction of AGN (e.g. Piconcelli
et al. 2005; Kaastra et al. 2014). The most powerful of these
winds, observed in 20–40% of local AGN (e.g. Tombesi et al.
2010) and in a handful of higher redshift objects (e.g. Chartas
et al. 2009; Lanzuisi et al. 2012), have extreme velocities (ultra-
fast outflows, UFOs, v 0.1-0.3c) and are made by highly ionised
gas which can be detected only at X-ray energies.
We collected from the literature observations of AGN with
reliable massive outflow detections, for which there is an es-
timate (or a robust limit) on the physical size of the high ve-
locity gas involved in the wind. The sample includes molecular
winds, ionised winds (from [OIII], Hα and Hβ lines), broad ab-
sorption line (BAL) winds and X-ray absorbers (both UFOs and
the slower “warm absorbers”). We give in Appendix A a short
description of the source samples used in the following analysis.
We have recomputed the wind physical properties (mass
outflow rate, kinetic energy rate) using the same assumptions
for all sources of each sample (as detailed in Appendix B).
While wind geometry, wind gas density, temperature, metallic-
ity etc. may well differ from source to source, applying a uni-
form analysis strategy minimizes systematic differences from
sample to sample. In fact, self-consistent information of the gas
physical and chemical properties is not available for the ma-
jority of the sources with detected winds, and thus assump-
tions on these properties must be done in any case. For ionised
wind parameters, the chain of assumptions needed to convert
observed quantities into physical quantities is particularly long
(see Appendix B), and therefore the largest uncertainties con-
cern these winds (about one order of magnitude or even more,
see Harrison et al. 2014). We also collected from the literature
AGN and galaxy properties, such as luminosities, SFRs, stel-
lar masses, molecular gas masses. We note that these quanti-
ties are calculated by different authors, using non-homogeneous
recipes. In particular, bolometric luminosity are calculated ei-
ther from fitting optical-UV spectral energy distributions (SEDs)
with AGN templates and from X-ray or infrared luminosities by
applying a bolometric correction. Most SFRs are calculated from
far infrared luminosities and therefore are not instantaneous
SFRs. Stellar masses are calculated from modelling optical-near-
infrared galaxy SEDs with galaxy templates or by converting
near infrared luminosities from IFU observations of nearby AGN
host galaxies into stellar masses. Molecular gas masses are cal-
culated converting CO luminosities into H
2
gas masses, by as-
suming a standard conversion factor (see Appendix for details).
This unavoidably introduces some scatter in the correlations dis-
cussed in the following sections.
Altogether, we have assembled a sample of 109 wind mea-
surements of 94 AGN with detected massive winds at different
scales (sub-pc to kpc) and ionisation states, that we use to con-
strain the relationships between wind parameters, AGN param-
eters and host galaxy parameters. This sample is definitely not
complete and suffers from strong selection biases; above all, we
note that most molecular winds and UFOs are found in local
ULIRGs and Seyfert galaxies. Ionised winds are found in both
low-redshift AGN and z = 2–3 luminous/hyper-luminous QSOs.
BALs are from z = 2–3 QSOs.
2.1. Wind parameters vs. AGN parameters
Figure 1 shows the wind mass outflow rate (left panel) and ki-
netic power (right panel) as a function of the AGN bolometric
luminosity. The mass outflow rate and kinetic power of molecu-
lar winds (blue symbols) are correlated rather well with the AGN
bolometric luminosity (see Table 1, which gives for each corre-
lation the Spearman rank, SR, correlation coefficient, the prob-
ability of the correlation and the best fit slope, obtained from a
least square fit between the two variables). The log linear slope
is 0.76 ±0.06 for the mass outflow rate and 1.27± 0.04 for the ki-
netic power. The average ratio
˙
E
kin
/L
bol
in the molecular winds
sample is 2.5%.
Ionised winds (green symbols), BAL winds (black symbols),
and X-ray absorbers (red symbols), lie below the correlation
found for molecular winds. Most ionised winds have
˙
M
OF
10–
100 times smaller than molecular winds at L
bol
<
∼
10
46
erg/s.
Above this luminosity, ionised winds have
˙
M
OF
similar or a
few times lower than molecular winds. There is a good cor-
relation between
˙
M
OF
,
˙
E
kin
, and the bolometric luminosity for
ionised winds (see Table 1) with log linear slopes 1.29 ± 0.38
and 1.50 ± 0.34 respectively. The average ratio
˙
E
kin
/L
bol
for the
ionised winds sample is 0.16% at log L
bol
= 45 and 0.30% at
log L
bol
= 47.
X-ray absorbers and BAL winds have respectively
˙
M
OF
∼
500, 30 times lower than what expected from the best fit lin-
ear correlation for molecular winds, again showing a trend for
higher differences with respect to molecular winds at lower bolo-
metric luminosities. About half X-ray absorbers and BAL winds
have
˙
E
kin
/L
bol
in the range 1–10% with another half having
˙
E
kin
/L
bol
< 1%.
The left panel of Fig. 2 show the AGN bolometric luminos-
ity as a function of the maximum wind velocity, v
max
, defined
following Rupke & Veilleux (2013) as the shift between the
velocity peak of broad emission lines and the systemic veloc-
ity plus 2 times the σ of the broad Gaussian component, see
A143, page 3 of 21
A&A 601, A143 (2017)
Fig. 1. Left panel: the wind mass outflow rate as a function of the AGN bolometric luminosity. AGN for which molecular winds have been reported
in the literature (mostly local ULIRGs and Seyfert galaxies) are shown with blue symbols. In particular: open circles are CO outflows; the open
square is the measurement for IRAS 23060; filled squares are OH outflows; the starred open circles are for Markarian 231 (large symbol for the
outflow measured within R
OF
= 1 kpc and small symbol for the outflow at R
OF
= 0.3 kpc); the crossed open circles are the measurements for
NGC 6240 (large symbol for R
OF
= 3.5 kpc and small symbol for R
OF
= 0.6 kpc); the small dotted open triangle marks the measurement in the
circum nuclear disk of NGC 1068 (R
OF
= 0.1 kpc) and NGC 1433 (R
OF
= 0.06 kpc); the small dotted open circles represent the measurements
for NGC 1266, IC 5066 at R
OF
= 0.5 kpc; the squared open circle marks IRAS F11119+13257 measurement at R
OF
= 0.3 kpc. Green symbols
mark ionised outflows measurements. In details: filled squares mark z > 1 AGN; filled triangles mark z = 0.1–0.2 AGN; open triangles mark
z = 0.4–0.6 type 2 AGN; pentagons mark z = 2–3 radiogalaxies; filled circles mark hyper-luminous z = 2–3 QSOs. BAL winds are shown with
black stars. The black open pentagon highlights the [CII] wind in J1148+5251 at z = 6.4. Finally, red symbols mark X-ray outflows. In details:
large five pointed stars are local UFOs; the starred open circle, the filled triangle and the circled square are the measurement for Markarian 231,
PDS456 and IRAS F11119+13257, respectively. Small five point stars are slower warm absorbers. The dashed blue, green and red lines are the
best fit correlations of the molecular, ionised, and X-ray absorber samples, respectively. Right panel: wind kinetic power as a function of the AGN
bolometric luminosity. Solid, dashed and dotted line represent the correlations
˙
E
kin
= 1, 0.1, 0.01 L
bol
.
Fig. 2. Left panel: AGN bolometric luminosity as a function of the maximum wind velocity, v
max
. The black dashed lines mark a v
5
max
scaling.
The magenta solid line is the best fit correlation found by Spoon et al. (2013) for OH outflows. The two cyan solid lines are the best fit scaling
found by Veilleux et al. (2013) for OH outflows, using v
max
and v
80
. The cyan boxes and filled dot are the loci covered by two groups of Swift BAT
AGN with 42.3 < L
bol
< 43.3 and 43.7 < L
bol
< 44.3 and by the outlier NGC 7479, from Stone et al. (2016). Right panel: wind momentum load
(outflow momentum rate divided by the AGN radiation momentum rate L/c) as a function of v
max
. The red dashed line mark the expectations for
a momentum conserving outflow. The two blue solid lines mark the expectations for pure energy conserving outflows for Markarian 231 (starred
circle) and IRAS F11119+13257 (squared circle). Symbols as in Fig. 1.
A143, page 4 of 21
F. Fiore et al.: AGN wind scaling relations
Fig. 3. Left panel: outflow kinetic power as a function of the star formation rate in the host galaxy (computed, when possible, in a region similar
to that where the outflow has been detected). The dashed line is the expectation of a SN-driven wind, by assuming 0.0066 SNe per solar mass of
newly formed star (Salpeter IMF) a total luminosity for each SN of 10
51
erg/s and an efficiency of releasing this luminosity in the ISM to drive a
shock of 10%. The solid red line is the expected SFR obtained using the Netzer (2009) relationship between SFR and AGN bolometric luminosity
and assuming the average
˙
E
kin
/L
bol
= 0.025 found for molecular winds in Fig. 1. Right panel: AGN bolometric luminosity as a function of the
host galaxy star formation rate. The red, magenta and cyan lines in the right panel are the expected relations based on the SFR−L
bol
correlations
by Netzer (2009), Hickox et al. (2014; z = 0) and Hickox et al. (2014, z = 2), respectively. Symbols as in Fig. 1.
the Appendix. v
max
correlates with the bolometric luminosity
for molecular winds, and ionised winds. Considering the two
winds together again produces a strong correlation and a log
linear slope of 4.6 ± 1.5 (see Table 1). For X-ray absorbers the
situation is more complex, since they are divided in two broad
groups, warm absorbers with lower velocities and UFOs with
higher velocities. For UFOs with v
max
> 10
4
km s
−1
the correla-
tion between AGN bolometric luminosity and maximum veloc-
ity is still remarkably strong, with a log linear slope of 3.9 ± 1.3
(Table 1), statistically consistent with that of molecular+ionised
winds. This means that at each given bolometric luminosity the
ratio between UFO maximum velocity and molecular-ionised
wind maximum velocity is similar, and equal to ∼40−50. We
also report in Fig. 2 the scalings found by Spoon et al. (2013)
and Veilleux et al. (2013) for OH outflows in samples of ULIRGs
and QSOs at z < 0.3. Four of the objects in Veilleux et al. (2013)
are also part of our sample, see Table B.1.
BALs and the lower velocity X-ray absorbers v
max
<
10
4
km s
−1
(the so called X-ray warm absorbers), also seem
to show a correlation between AGN bolometric luminosity and
maximum velocity, with a slope close to the fourth-fifth power,
with the warm absorbers present in low luminosity systems and
BALs present in high luminosity systems.
The right panel of Fig. 2 shows the wind momentum load
(i.e. the wind momentum rate,
˙
P
OF
=
˙
M
OF
× v
max
, divided by the
AGN radiation momentum rate,
˙
P
AGN
= L
bol
/c) as a function of
v
max
(see also Stern et al. 2016). The blue solid lines are the ex-
pectations for energy conserving winds (
˙
P
OF
/
˙
P
AGN
≈ v
UFO
/v
OF
)
for the cases of Markarian 231 and IRAS F11119+13257, the
only two sources for which both X-ray winds and molecular
winds have been detected (Tombesi et al. 2015; Feruglio et al.
2015). Molecular winds have momentum load in the range 3–
100, about half have momentum load >10, suggesting again that
most massive-extended outflows are not momentum conserving
but rather energy conserving winds, extended on the host galaxy
scales.
Ionised winds have velocities intermediate between molec-
ular winds and X-ray absorbers. The range of their momentum
load is wide, from 0.01 to 30. Most BAL and X-ray winds have
˙
P
OF
/
˙
P
AGN
<
∼
1, suggesting that they are probably momentum
conserving, as predicted by the King (2003) model.
2.2. Wind parameters vs. host galaxy star formation rate
We now study the correlations between massive, extended
winds, i.e. molecular and ionised winds, and the properties of
their host galaxies.
Figure 3 shows the outflow kinetic power and AGN bolomet-
ric luminosity as a function of SFR in the host galaxy (correla-
tion coefficients given again in Table 1). There is a loose corre-
lation between log(
˙
E
kin
) and log(SFR). It should be kept in mind
that the SFR plotted in Fig. 3 is, in most cases, not the instan-
taneous SFR but rather the conversion from the observed FIR
luminosity. The instantaneous SFR can be zero in these systems,
and what we are observing is light from stars born hundreds of
millions of years before the AGN shutting off and its feedback.
This SFR is therefore an upper limit to the on going SFR. Indeed,
Davies et al. (2007) found that the on going SFR in the nuclei of
Markarian 231 and NGC 1068 is probably very small, because
of the small observed Brγ equivalent width within 0.1–0.5 kpc
from the active nucleus.
A correlation between
˙
E
kin
and SFR would naturally emerge
if winds were supernova (SN) driven. The dashed line in Fig. 3,
left panel, is the expectation for SN-driven winds, by assuming
0.0066 SNe per solar mass of newly formed star (Salpeter IMF),
a total luminosity for each SN of 10
51
erg/s, and a 10% efficiency
in releasing this luminosity into the ISM to drive a shock. The
SN rate per solar mass is 0.0032 and 0.0083 M
−1
for a Scalo and
Chabrier IMF, respectively (Somerville & Primack 1999; Dutton
& van der Bosh 2009). Therefore, SNe do not seem powerful or
numerous enough to drive most observed winds.
A143, page 5 of 21