NASA Technical Reports Server (NTRS) 20120015661: On the X-Ray Low- and High-Velocity Outflows in Active Galactic Nuclei

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ROrAl. ASTRONOM[CAL SQCIiITY
Mon. Not. R. Astron. Soc. 4U, L64-L68 (2012) doi:l0.llll/j.1745-3933.2011.01180.x
On the X-ray low- and high-velocity outflows in active galactic nuclei
J. M. Ramirezl* and F. Tombesi2
,3
1L eibniz-/nstitut flir Astrophysik Potsdam, An der Sternwarte 16, D·14482 Potsdam, Germany
2DepartmenJ of Astronomy and CRESsr, University ofM aryland, College Park. MD 20742, USA
3Laboratory for High Energy Astrophysics, NASNGoddard Space Flight Center, Greenbelt, MD 20771, USA
Accepted 2011 October 21. Received 2011 October 20; in original form 2011 September 11
ABSTRACT
An exploration of the relationship between bolometric luminosity and outflow velocity for
two classes of X-ray outflows in a large sample of active galactic nuclei has been performed.
We find that line radiation pressure could be one physical mechanism that might accelerate
the gas we observe in warm absorber, v ~ 100-1000 km S-l , and on comparable but less
stringent grounds the ultrafast outflows, v ~ 0.03--D.3c. If comparable with the escape velocity
of the system, the first is naturally located at distances of the dusty torus, '" I pc, and the
second at subparsec scales, "'0.01 pc, in accordance with large set of observational evidence
existing in the literature. The presentation of this relationship might give us key clues for
our understanding of the different physical mechanisms acting in the centre of galaxies, the
feedback process and its impact on the evolution of the host galaxy.
Key words: black hole physics - galaxies: active - X-rays: galaxies.
interpreted as due to resonant absorption from Fe XXV-XXVI associ
1 INTRODUCTION
ated with a zone of circumnuclear gas photoionized by the central
s '"
Mildly relativistic and non-relativistic absorption troughs are ob X-ray source, with ionization parameter log 3-6 erg S-l cm and
served in the X-ray spectra of active galactic nuclei (AGNs). A column density NH '" 1()22-1()24 cm-2. The energies of these ab
qualitative separation is usually done between classical v '" 100- sorption lines are systematically blueshifted and the corresponding
1000kms-1 warm absorbers, which we refer to (throughout this velocities can reach up to mildly relativistic values of "'0.03e-O.3e.
Letter) as low-velocity outflows (Blustin et aL 2005; McKernan, These findings are important because they suggest the presence of
Yaqoob & Reynolds 2007), and ultrafast outflows (UFOs) v > previously unknown massive and highly ionized absorbing material
10000 km S-I, which we refer to as high-velocity outflows (Tornbesi outflowing from their nuclei, possibly connected with accretion disc
et al. 20IOa,b). winds/ejecta (e.g. King & Pounds 2003; Proga & Kallman 2004;
On one hand, the extracted velocity from the classical v '" 100- Sim et al. 2008, 2010.; Ohsuga et al. 2009; King 201Ob).
1000kms-1 warm absorber is mainly obtained using the Fe M Several acceleration mechanisms have been proposed to explain
she1l2p-3d unresolved transition array (Behar, Sako & Kahn 2001; these outflows: (1) thennally accelerated winds (Krolik & Kriss
Ramirez etaL 2008) and o VII or o VIII resonance lines (e.g. George 2001); (2) radiation pressure through Thomson scattering and mag
et al. 1998; the hallmark of the classical warm absorber). The spatial netic forces (MHO; Ohsuga et al. 2009) and (3) radiation pressure
location of this absorbing material is uncertain. Models of X-ray due to the absorption of spectral lines (e.g. Proga & Kallman 2004;
absorbers in AGN place them at a wide range of distances from Ramirez 2008, 2011; Schurch, Done & Proga 2009; Sim et al.
the central source. Specifically. they are suggested to be winds 201Ob). Although the first one can explain the velocities we ob
originating from the accretion disc (Murray et al. 1995; Elvis 2(00), serve in the low-velocity outflows, it can be excluded because it
located at the dusty (-I pc) torus scales (Krolik & Kriss 2001) or cannot explain the "'O.lc-O.2e we observe in UFOs (Tombesi et aI.
even beyond the narrow-line region (e.g. Ogle et al. 2000). 201Oa,b). Ohsuga et al. (2009) seem to reproduce the velocities ob
On the other hand, blueshifted Fe K absorption lines have been served in low-and high-velocity outflows. On the other hand. Arav,
detected in recent years at E > 7 keVin the X-ray spectra of sev Li & Begelman (1994), Ramirez (2008), Saez. Chartas & Brandt
eral radio-quiet AGNs (e.g. Chartas et al. 2002; Chartas, Brandt & (2009) and Chartas et al. (2009) invoke radiation pressure due to
Gallagher 2003; Pounds et al. 2003; Dadina et al. 2005; Markowitz, lines to explain the "'O.2e outflow detected in a good signal-to-noise
Reeves & Braito 2006; Braito et al. 2007; Ramirez 2008; Cappi et al. ratio X-ray spectrum of a high-z quasar (the broad absorption line,
2009; Reeves et al. 2009: Tombesi et al. 201Oa,b). They are usually APM 08279+5255), and they reproduce, as part of the procedure,
the Fe XXV-XXVI lines detected at E > 7 k.e V. Here we focus on this
kind of approach, since it allows us to explore, very efficiently, a
*E-mail: [e-mail] wide range of physical parameters of the system.
«:> 2011 The Authors
Monthly Notices of the Royal Astronomical Society 0 2011 RAS
Low- and high-velocity outflows L65
The goal of this Letter is to place a proof of idea for a sys absorbers are highly ionized, with log; ,...., 3-6 erg S-l cm, and have
tematic study about the operating acceleration mechanisms in both large column densities, in the range NH ,...., 1022_1024 cm-2.
X-ray low- and high-velocity outflows, using an.anisotropic radia The 5MBH masses of the Seyferts in the Tombesi et al. (20IOb)
tive pressure framework (e.g. Proga, Stone & Kallman 2000; Proga sample have a mean value of MBH = S.3 X 10' Me:) (Marchesini,
& Kallman 2004; Liu & Zhang 2011), beginning with line radiation Celotti & Ferrarese 2004; Peterson et al. 2004).
pressure. When computing the energetics of these outflows, we see
We present the observables from which we build the model that these are more massive than the low-velocity ones, Mout "-'
in Section 2. The details of the proposed model are presented in 0.1-lM0yr-1 rv MIllX), and also much more powerful, with a
Section 3. The results and the discussion are in Section 4. We sum mechanical power of "-'1043_Hr5 erg S-I (e.g. Pounds et al. 2003;
marize in Section S. Markowitz et al. 2006; Braito et al. 2007; Cappi et al. 2009; Tombesi
et al. 201 Ob). The latter value is "-'S-lO per cent of the bolometric
luminosity. Therefore, the high-velocity outflows may potentially
2 OBSERVABLES play an important role on the expected cosmological feedback from
AGNs (e.g. King 20IOa,b).
In this section we present the observables of the two types of out
flows, since they are the initial motivation for the proposed model.
3 THE MODEL
2.1 The low-velocity outftows We build our model based on observational evidence, basically
from two sources: Blustin et al. (200S) for the classical v ,...., 100-
When describing the physical conditions of wann absorbers, it is
1000 km S-1 wann absorbers, referred here as low-velocity outflows,
common to use the definition of ionization parameter ~ = 4~:Qn andTombesietal. (20IOb) for the UFOs v;>: 10000kms-I, referred
(Tarter, Tucker & Salpeter 1969), where F ion is the total ionizing here as high-velocity outflows.
flux (Fion = Lion/4nr2) and nH is the gas density. The source As we see, together the two classes of outflows cover a wide
spectrum is described by the spectral (specific, energy-dependent
range in velocity and black hole masses. We seek a physical model
e) luminosity Lf. = Liorfo where Lwn is the integrated luminosity
IioooR,d which provides the context to explain (to first approximation) part
from 1 to 1000 Ryd, and l,dE = 1.
of the observational evidence we have up to now.
So we describe the ...... 1000 km S-I wann absorber outflows as ab In order to do that, and to gain some insight into the relation
sorbing material around a supermassive black hole (SMBH) with
mass MBH - 3 X 107 (Peterson et al. 2004; BIustin et al. 2(05), col vsheilpo cbiteytw peroenfi loeu atfsl oaw f uvnelcoticoitny o(vf oruatd) iaunsd, gluivmeinn obsyit yh,y wdreo dinyvnoakme itchael
umn density of the absorbing material NH ,...., 1020_1022 cm-2, flow calculations (Proga et al, 20(0). The mathematical shape of the
ing outwards at velocities v - 1O()-2000kms-1 (e.g. Kaspi et al.
relation is given by assuming an outflow accelerated by radiation
2002; Krongold et al. 2003, 2005; Ramirez, Bautista & Kallman
pressure from a central source with a bolometric luminosity Lbol
200S), at medium ionization states log ~ ,...., .0-3 erg S-1 cm (Blustin and a mass of MBH:
et al. 2005). (1 1)] 1/2
MoWut h~e n0 .c6oMmp0u ytinegl , trhaet ioesn eorfg Metiocust ,t ot haecyc rfeitnido nmraatsess-2l oMsso utr/a MteIs/X o ~fl Vout[i] = [ 2GMBH[i] ( rLLf Edd~[[.,]] - 1) -R;.n - -R , (1)
=
5 and kinetic 1uminositr LEK Mmt2, of the orders of 1(J38- where LEdd is the Eddington luminosity, r f is the force multiplier,
UrI erg S-I, representing less than 1 per cent of the bolometric where the acceleration due to the absorption of discrete lines is
luminosity (Blustin et al. 2(05). The main conclusion from these encapsulated (Laar & Brandt 2002), Rin is the radius at which the
estimations is that these outflows contributes little to the energy wind is launched from the disc, and R is. the distance of the accel
injected in to the host galaxy. But the amount of matter processed erated portion of the outflow from the central source. The index i
over the AGN lifetime can be significant (also in accordance with runs simultaneously over the two distributions: velocitylBH mass.
Krongold et a!. 2007, for instance). Assuming that we observe the gas when it has reached the terminal
velocity of the wind, i.e. Vout atR = 00, we can write
(voo Rio 1) .
2,2 The high-velocity outflows L"",[i] = LEdd[i] ,[i]2 +
r, (2)
2GM [i]
The characteristics of the UFOs with v;>: 10000kms-1 (;>:0.03c) BH
can be derived from the blueshifted Fe XXV-XXVI absorption lines Now we have the basic ingredient of the model, and we are ready
detected by Tombesi et a!. (20IOb) in a complete sample of local to build our two classes of outflows.
Seyfert galaxies. Such features are detected in ,....,40--60 per cent Set 1: high velocity. This synthetic sample is composed from 1000
=
of the sources, which suggests a covering fraction of C ,...., 0.5. black holes with masses normally distributed with mean li-m 2.6 X
Tombesi, Cappi & Reeves (2011) also performed a photoionization 107 Me:) and standard deviation u m = 1.3 X 107 Me:).4 Also we use
modelling of these lines. They derived the distribution of the outflow a normal distribution for the outflow velocity of the absorbing gas
velocities, which ranges from "-'0.03c up to mildly relativistic values around the BH with /L, = 57 OOOkm S-I (this is the best-fitting value
of """O.3c, with a peak and mean value at ,....,0. 14c. As expected, these for set l)anduv = lS000kms-l.
=
4We take the middle point (ILm 2.6 x lQ'M0) between the mean ex
I Mean of the Moot reported by Blustin et al. (2005) in their table 4, excluding tracted from Tombesi et al. (2011) (ILm = 5.3 x 107 M0), excluding the
Ark 564 (outlier Mout = 23M0 yel). mass of Mrk 205 (outlier MBH = 44 X 10' M0), and the mean extracted
2 Mean of the Moud Mace reported by Blustin et al. (2005) in their table 4, from table 5 of Blustin et al. (2005) (ILm = 2.7 x 107 M0), excluding the
excluding Ark 564 (outlier MoudM ace = 550). mass of IRAS 13349+2438 (outlier MBH = 80 X 107 M0)' Also we take
=
3 Excluding PG 0844+349 and PG 1211+143. the larger value of the observed dispersion O"m(obs) 1.3 x 10' M0.
10 2011 The Authors, MNRAS 419, L64-L68
Monthly Notices of the Royal Astronomical Society 0 2011 RAS
L66 J. M. Ramirez and F. Tombesi
,
Sol' 801'
..
-o Bh"dn III Ill. 2005
~.
il l
P I~ i
, I
tVl
~ "V
J
~ ,I 1
. \
O.Oe+OO 1.0e+46 2.0e+46 O.Oe+OO· 1.0e+46
O.Oe+oo 1.09+45 2.09+45 Lool (erg/a) "'" (e"".)
loot (erg/s) "'" (e"".)
Figure 2. Theoretical versus observational outflow velocity against lumi
Figure 1. Velocity of the outflow versus the bolomett'ic luminosity needed nosity. Ellipses (10', 20' and 30' contours of the model) are thooretical
to accelen:te the wind. Filled circles are the velocities observed if we see calculations coming from two samples of outflows -left-hand panel: high
the wind a;ong the flow. Open squares are including the effects of random velocity (set 3, i.e. including the effects of random lines of sight) and rigbt
lines of siEht (see text for discussion). band panel: low velocity (set 4, i.e. including the effects of random lines of
sight). Open squares are observational points from the XMM-Newton radio
quite samplo of Tombesi et al. (2011), for the UFOs. The open diamonds
Set 2: lov.l velocity. In this case we use 1000 black holes with masses
are points compiled by Blustin et al. (2005).
nonnaliy distributed with the same mean, J.l-m = 2.6 X 107 Me::>. and
u
standard deviation, m = 1.3 X 107 M0. as before but we use a ity, i.e. vobs = VoutCOS (J, where (J is the angle between the outflow
nonnal d:stribution for the outflow velocity of the absorbing gas
direction and the line of sight. Then using the same luminosities
around the BH with f.i,v = 1800 kIn 8-1 (this is the best-fitting value produced by set 2, but plotting (open squares) against 1000 v,,,,(s)
forset 2) and", = 600 km S-I.
= randomly computed using a random generator of numbers (with
The best·fitting values of ~,(l) and ~,(2) [as well as r,(l) 250
'!t/12 ~ (J ~ '!t/2),5 and equation (2) with Vobs = Voutcos(J, we
and r f(2) = 40; see next section] are estimated by comparing a grid
produce the subsample set 4. It is easy to see that set 4 resembles
of model; computed using 10000::: ~,(1)::: 70000 (kms-I) and
100 :s. JL.[ (2) ::::: 2000 (lem 5-1), with the corresponding set of obser better the plot shown in fig. 4 of Blustin et al. (2005), taking into
account the possible incompleteness of the sample.
vation: set 3 versus Tombesi et al. (2011) and set 4 versus Blustin
Doing the same for the UFOs, we use the luminosities produced
et al. (2005). We performed the comparison using a Kolmogorov
Smirnovtest. We take the ~,(l) and ~,(2) [as well as r,(1) = 250 by set 1 (rf = 250, this is the best-fitting value for set 1 and set
and r (2) = 40; see next section] which give maximump-values of 3; see section 3) but plotting (open squares) against 1000 Vobs(S)
f randomly computed using a random generator of numbers (with
the test. The final p-value for the comparison set 3 versus Tombesi
",/12 ::: 9 ::: ",/2). and equation (2) with v,'" = voo,cos9, to
et al. (20ll) gives 0;0.8 (D = 0.16) and for the set 4 versus Blustin
= produce the subsample set 3. In this case, set 3 better resembles the
et al. (2005) 0;0.07 (D 0.38).
relationship between Voul and luminosity (see Fig. 2 ).
The launching radius, Rin• for each set of simulations is based In Fig. 2, we place both classes of outflows together along with
on the results of Blustin et al. (2005) for set 2, i.e. R;n(set2) = 1 pc
observational points taken from two samples of objects: 14 points
(orders of magnitude value). For set 1, we set Rin(setl) = 0.01 pc,
out of the 23 objects reported by Blustin et al. (2005) (the others
based on Tombesi et al. (201Oa,b).
either did not report outflow velocity or were unknown), in the right
hand panel, and 19 points from the sample of 19 objects where UFOs
have been detected by Tombesi et al. (2011), in the left-hand panel.
4 RESULTS AND DISCUSSION
There are several interesting facts about the plot: (1) the obser
In this section we discuss the results of our simulated samples and vational points cover R::3.8 orders of magnitude in velocity; (2)
summarize their physical context and implications. they cover R::3 orders of magnitude in bolom.etric luminosity (from
Fig. 1 shows the theoretical relationship between outflow velocity _1043 to lQ'6ergs-l) and (3) that our proposed model is able to
and bolometric luminosity. reproduce most of the low-velocity points (11/14) (two of the points
The curvature we see in Vout of set 2 (and also set I, filled circles, migbt fall in the high-velocity set instead) and, less stringently, half
our line of sight is along the flow; see below) is due to the quadratic of the points for the higb-velocity set (11/19), using one physi
dependence of the luminosity with Vout given by equation (2). It is cal acceleration mechanism and three free parameters: mass of the
worth noting that if we assume a force multiplier of r f = 40 (this is BH (M'H), outflcrw velocity (v,,,,) and force multiplier (rr). On
the best-fitting value for set 2 and set 4; see Section 3), we are able the other hand, there are two sectors where the deviations between
to reprod:lce the range of luminosities seen in fig. 4 of Blustin et al. model and theory are large: (1) the higb velocityllow luminosity
(2005). and (2) the low velocitylhigh luminosity, both requiring a closer
On the other hand, this model is not reproducing well the dis inspection to the completeness of the samples andlor the addition of
persion we observe in fig. 4 of Blustin et aI. (2005), which could other acceleration mechanisms, like magnetic thrust, for instance.
be explained by the fact that equation (2) will give radially acceler But, this may be the topic of future work.
ated flows, or in other words, that we are observing all the objects
radially along the flow. To include the effect of observing random
lines of sight transversely through different sections of the flow, we 5 The lower limit assumes that the torus covers """300, so we are able to
connect the observed velocity Vobs with the intrinsic radial veloc- observe the outflow only from () :::: 7t/12.
@ 2011 The Authors, MNRAS 419, L64-L68
e
Monthly Notices of the Royal Astronomical Society 2011 RAS
Low- and high-velocity outflows L67
4.1 Anisotropic radiation pressure picture from the referee which helped to improve several aspects of the
work. Ff provided the data based on observations obtained with the
We propose here that the low- and high-velocity outflows can be
XMM-Newton satellite, an ESA funded mission with contributions
accelerated by the same physical mechanism (as is suggested by
by ESA member states and USA. FT acknowledges support from
Fig. 2), i.e. radiation pressure, and that the differences depend
NASA through the ADAPILTSA programme. This research bas
on the 'Values of the three fundamental parameters: mass of the
mede use of the NASAIlPAC Extraga1actic Database (NED) which
BH (MBH), the object luminosity (Lbo!) and force multiplier (r,). is operated by the Jet Propulsion Laboratory, California Institute
The va/i.,es of r F we have used are of the orders of those found in
of Technology, under contract with the National Aeronautics and
observarional (e.g. Laor & Brandt 2002) and theoretical (e.g. Saez
Space Administration.
et al. 2011) works. However, detailed photoionization computations
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02011 The Authors, MNRAS 419, L64-L68
Monthly Notices of the Royal Astronomical Society 0 2011 RAS