Ultra-fast outflows (aka UFOs) from AGNs and QSOs

0.31 MB·English

by  M. Cappi

Mem.S.A.It.Vol.84,1
(cid:13)c SAIt 2008 Memoriedella
Ultra-fast outflows (aka UFOs)
from AGNs and QSOs
M. Cappi1,F. Tombesi2,3,andM. Giustini4
3
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1 INAF/IASF-Bologna,ViaGobetti101,I-40129,Bologna,Italy
2
2 NASAGoddardSpaceFlightCenter,Greenbelt,MD20771,USA

n 3 DepartmentofAstronomy,UniversityofMaryland,CollegePark,MD20742,USA
a 4 ESAC/ESA,POBox78,E-28691VillanuevadelaCanada,Madrid,Spain
J e-mail:[email protected]

0
3
Abstract. Duringthelastdecade,strongobservationalevidencehasbeenaccumulatedfor
] theexistenceofmassive,highvelocitywinds/outflows(akaUltraFastOutflows,UFOs)in
E
nearbyAGNsandinmoredistantquasars.Herewebrieflyreviewsomeofthemostrecent
H
developments in this fieldand discuss the relevance of UFOsforboth understanding the
. physicsofaccretiondiskwindsinAGNs,andforquantifying theglobalamount ofAGN
h
feedbackonthesurroundingmedium.
p
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o Keywords.X-rays:Galaxies–Galaxies:nuclei–Galaxies:quasars:absorptionlines
r
t
s
a
1. Introduction temporary satellites such as XMM-Newton,
[
SuzakuandChandra,gasatevenhigherioniza-
Mass outflows/winds have been found in all
1 tionstate(i.e.FeXXV,FeXXVI),columnden-
v types of AGNs and QSOs. Despite being ra- sity (N ∼1022−23cm−2)and withmuchhigher
9 diativelydark/silent,theyhaverevealedthem- velocitiWes (v∼0.05-0.3c)has been observed in
9 selvesviablue-shiftedabsorptionfeaturesim-
a number of AGNs/QSOs at both low and
1 printed on the source UV and X-ray con-
high redshift (Pounds et al. 2003; Chartas
7 tinua(seeCrenshaw,Kraemer&George2003
et al. 2002; Tombesi et al. 2010 and ref-
.
1 for a review). Once corrected for sample se- erences therein). Here some recent develop-
0 lection biases, intrinsic UV absorption lines
ments in this field are presented (§2) with a
3 blue shifted by 103−5 km s−1 are generally
particular emphasis on their importance for
1 foundinabout50-60%ofallAGNs(Ganguly
our understanding of accretion disk forma-
:
v & Brotherton 2008, Hamann et al. 2012). tion/acceleration (§3), and their (global) rele-
Xi Similarly, in X-rays, warm absorbers (WAs) vanceforAGNfeedback(§4).
havebeenobservedinabout50%ofbrightlo-
r cal AGNs and more distant QSOs (Reynolds
a 2. RecentResults
1997;McKernanetal.2007;Porquetal.2004;
Piconcelli et al. 2005). In the last decade, Systematic studies with XMM-Newton have
thankstothehighthroughputprovidedbycon- found that as many as ∼40% of local (z<0.1)
AGNsshowevidenceforhighly-ionized,high-
Sendoffprintrequeststo:M.Cappi velocity Fe absorption lines interpreted as
2 Cappi:UFOsinAGNsandQSOs
Fig.1.Distributionsofmeanabsorberparameters:(a)logarithmofthemeancolumndensity;(b)logarithm
ofthemeanionizationparameter;(c)logarithmofthemeanoutflowvelocity.Thered,greenandbluecolors
indicatetheSuzakuanalysis,whilethedotted(black)linesaretheXMM-Newtonanalysis(fromGofford
etal.2012).
ultra-fastoutflows(UFOs)fromthecentralnu- of both months and hours, best reproduced
cleus (Tombesi et al. 2010). More recently, by means of variableand massive ionizedab-
a new systematic study has been conducted sorbers along the line of sight (Giustini et al.
by Gofford et al. (2013) using also archival 2011).InparticularthehighestS/Npartofthe
datafromtheSuzakuspaceobservatory,allow- observation has shown clear evidence in the
ing for a wider (0.6-50 keV) energy band, a highest energy band (E>5 keV) for the pres-
high throughput up to 8-9 keV, several inde- ence of a ultra-fast outflow with velocity of
pendentinstruments(XIS0/1/2/3)andadiffer- ∼ 16500 km s−1 variable on very short time
ent but comparable sample of (51 type 1-1.9) scalesofafewks(seeFig.2).
AGNs.Thisstudywasuniqueinitswaytover- Even if the fraction of QSOs with UFOs
ify, complement and possibly expand on the remains to be determined yet, these findings
previous XMM-Newton results. Remarkably, are qualitatively consistent with AGN-driven
the results (see Fig. 1) are entirely consistent accretion disk winds scenarios,and are point-
with the XMM-Newton ones independently ing to a phenomenonwhich couldbe actually
providing strong supporting evidence for the present/effectiveinalargefractionofallAGNs
existenceofveryhighly-ionisedcircumnuclear andQSOs.Theseobservationshavepavedthe
materialinasignificantfractionofbothradio- way to, but also shown the need for, more
quietandradio-loudAGNinthelocaluniverse. sensitiveobservationsandmoretime-resolved
Infainter,moredistantQSOs, X-raystud- spectralanalysisinthefuture.
ies have been generally limited by the low
3. UnderstandingUFOs
statistics. However, after the seminal works
on the few brightest, because lensed, quasars In an attempt to understand the global ori-
(Chartas et al. 2002, 2003, 2007), new ob- gin of these winds, in particular which of the
servations of non-lensed QSOs with higher possible physical mechanism(s) (heating, ra-
enough S/N are now starting to emerge. Two diation, and/or magnetic fields) is responsible
interesting examples are: i) HS 1700+6416 for their formation and acceleration, Tombesi
(z=2.73),thefourthhigh-zquasarthatdisplays et al. (2013) have compared the properties of
X-raysignaturesofvariablehigh-velocityout- UFOs to those of lower ionization and lower
flows (UFOs), which is the only one that is velocities WAs. Their observed properties (ξ,
not lensed (Lanzuisi et al. 2012); and ii) re- N , and velocities), as well as the rough es-
W
sultsofamulti-epochobservationalcampaign timates for their distance, mass outflow rate
with XMM-Newton on the mini-BAL QSO and kinetic energy, span over several order
PG1126-041(z=0.06)whichhasshowncom- of magnitudes. This allows the authors, for
plex X-ray spectral variability, on time scales the very first time, to compare their global
Cappi:UFOsinAGNsandQSOs 3
Fig.3. (Top):Schematicviewofanaccretiondisk
Fig.2. (Top): 0.2-10 keV EPIC-pn light curve of wind by an observer located top right and look-
PG1126-04.(Bottom):Theleftcolumnshowsthe5- ing through the wind, thereby probing UFOs/WAs
9keVEPIC-pnspectralresidualsforthefour(color- absorption features from the inner/outer parts of
coded)timeslicesshowninthetoppanel.Thisev- the wind. (Middle): Absorber ionization state vs.
idences the presence of Fe K absorption variabil- distance from the central source (in units of
ityoververyshort(∼ks)timescales.Therightcol- Schwarzschild radius). The blue, green and red
umnreportsthe90%and68%confidencelevelsfor points indicate thehighly ionized UFOs,the inter-
the energy and normalization of Gaussian absorp- mediate ionization absorbers and the lowerioniza-
tionlinesusedtomodeltheresidualsineachslice. tionWAs,respectively.Thesolidlinerepresentsthe
The strong variability of this highly-ionised (log ξ best-fit linear correlation curve. (Bottom): Kinetic
∼3.5ergcms−1)andhighly-massive(N ∼7×1023 powervs.outflowvelocity(figuresfromTombesiet
W
cm−2)phaseofthewindoververyshorttimescales al.2013)
(afewks)isevident(fromGiustinietal.2011).
among different parameters - and their slopes
- appear to be consistent with radiation pres-
properties to theoretical calculations and ten-
surethroughComptonscatteringorMHDpro-
tativelyderiveaunifyingpicture.Remarkably,
cessesbeingresponsiblefortheoutflowaccel-
alltheabsorbersarefoundtopopulateroughly
eration.Buttherearealsotemptingindications
continuouslythe whole parameterspace, with
thatbothprocessescouldbeactingsimultane-
UFOs observable closer to the central black
ously,withtheMHDregimeplayingasubstan-
hole, with higher ionization, column density,
tial role (Tombesi et al. 2013). Clearly, more
outflow velocity and mechanical power than
dataandbettermeasurementsareneededfora
WAs. These evidences strongly suggest that
more detailed and complete comparison with
these absorbers, often considered of different
theoretical expectations (i.e. Sim et al. 2010;
types,couldactuallyrepresentpartsofasingle
Fukumuraetal.,2010,Kazanasetal.2012).
large-scalestratified outflow,where UFOs are
likely launched from the inner accretion disk
4. ImpactonAGNFeedback
while theWAs atlargerdistances, suchasthe
outer disk and/or the putative obscuring torus As a ”by-product” of the above studies, and
(see Fig. 3). So far, the observed correlations expanding significantly upon other attempts
4 Cappi:UFOsinAGNsandQSOs
(i.e.Crenshaw&Kraemer,2012),thepotential
globalimpactofwinds(fromWAstoUFOs)to
AGN feedback was also estimated somewhat
quantitatively in Tombesi et al. (2013). This
workhasshownthatmostoftheoutflows,es-
pecially the UFOs, are able to provide a me-
chanical power of at least ∼0.5% and up to
several% of the AGN bolometric luminosity
(Fig. 4), thereby releasing considerable feed- Fig.4. Outflows kinetic power withrespect to the
back of energyand momentum into the inter- AGN bolometric luminosity (from Tombesi et al.
stellar medium of the host galaxy. Stimulated 2013). The points correspond to the WAs (red
bythesefindings,recent3-Dgrid-basedhydro- opencircles),non-UFOs(greenfilledtriangles)and
dynamicalsimulationsbyWagneretal.(2013) UFOs (blue filled circles), respectively. The trans-
have demonstrated that, on kpc scales, feed- verse lines indicate the ratios between the outflow
mechanical power and bolometric luminosity of
back by UFOs operates similarly to feedback
100% (solid), 5% (dashed) and 0.5% (dotted), re-
by relativistic AGN jets, and that considering
spectively.
thecommonoccurrenceofUFOsinAGN,they
are likely to be importantin the cosmological
feedback of galaxy formation. Whether these References
outflows could also contributesignificantly to
Chartas,G.etal.2002,ApJ,579,169
energize and enrich the intergalactic medium
Chartas,G.,Brandt,W.N.&Gallagher,S.C.,2003,
ofgroupsand/orclustersremainstobeunder-
ApJ,595,85
stood(butseeGasparietal.2012) Chartas,G.,etal.,2007,AJ,133,1849
Crenshaw, D.M., Kraemer, S.B., & George I.M.,
2003,ARA&A,41,117
Crenshaw,D.M.,&Kraemer,S.B.,2012,ApJ,753,
5. Conclusions
75
Fukumura,K.etal.,2010,ApJ,715,636
There have been significant advances in the
Ganguly,R,&Brotherton,M,2008,ApJ,672,102
last few years in characterizing the global Gaspari, M., Brighenti, F.& Temi, P., 2012,
properties of AGN winds, in particular from MNRAS,424,190
their most ”extreme” components probed by Giustini,M.,etal.,2011,A&A,536,49
their X-ray absorption features. Evidences of Gofford, J., et al. 2012, in ”AGN winds in
UFOs in nearby AGNs have become robust, Charleston” ASP Conference Series, Eds. G.
and some are emergingin an increasingnum- Chartas,F.Hamann,andK.Leighly,vol.460
Gofford, J., et al. 2013, MNRAS, in press
ber of QSOs too. Some recent studies based
(arXiv:1211.5810)
on both observations and theoretical simula-
Kazanas,D.,etal.,2012,AstrRv,7,92
tions have just started tackling the physical
Lanzuisi,G.,etal.,2012,A&A,544,2L
mechanismsatworkinacceleratingtheseout-
McKernan,B.,etal.,2007,MNRAS,379,1359
flows. Other studies have also demonstrated Piconcelli,E.,etal.,2005,A&A,432,15
that UFOs could play a major role in pro- Porquet,D.,al.2004,A&A,422,85
viding enough momentum and energy feed- Pounds,K.,etal.,2003,MNRAS,345,705
back to quench the galaxy star formation. Reynolds,C.,1997,MNRAS,286,513
In the near-future, X-ray observations with Sim,S.A.,etal.,2010,MNRAS,404,1369
TombesiF.,etal.,2010,A&A,521,57
micro-calorimeters(ASTRO-H) will certainly
TombesiF.,etal.,2011,ApJ,742,44
reduce further current uncertainties in the
TombesiF.,etal.,2012,MNRASLetter,422,1
UFOs parameter-space. Multi-frequency ob-
Tombesi, F., et al., 2013, MNRAS, in press
servations and monitoring of nearby AGNs
(arXiv:1212.4851)
willalsobeclueinunderstandingtheevolution Wagner, A.Y., Umemura, M., & Bicknell, G.V.,
ofthenuclear(sub-pc)UFOsintothelarger(pc 2013,ApJL,763,18
andkpc)scales.