the quasar outflow contribution to agn feedback: vlt measurements of sdss j0318-0600

21 Pages·2010·2.09 MB·English

TheAstrophysicalJournal,709:611–631,2010February1 doi:10.1088/0004-637X/709/2/611
(cid:2)C2010.TheAmericanAstronomicalSociety.Allrightsreserved.PrintedintheU.S.A.
THEQUASAROUTFLOWCONTRIBUTIONTOAGNFEEDBACK:VLTMEASUREMENTSOF
∗
SDSSJ0318-0600
JayP.Dunn1,ManuelBautista1,2,NahumArav1,MaxMoe3,4,KirkKorista2,ElisaCostantini5,ChrisBenn6,
SaraEllison7,andDougEdmonds1
1DepartmentofPhysics,VirginiaTech,Blacksburg,VA24061,USA;[email protected],[email protected],[email protected]
2DepartmentofPhysics,WesternMichiganUniversity,Kalamazoo,MI49008-5252,USA;[email protected],[email protected]
3DepartmentofAstrophysicalandPlanetarySciencesandCenterforAstrophysicsandSpaceAstronomy,UniversityofColorado,389-UCB,
Boulder,CO80309,USA
4Harvard-SmithsonianCenterforAstrophysics,Cambridge,MA02138,USA;[email protected]
5SRONNationalInstituteforSpaceResearch,Sorbonnelaan2,3584CAUtrecht,TheNetherlands
6IsaacNewtonGroup,Apartado321,E-38700SantaCruzdeLaPalma,Spain
7DepartmentofPhysicsandAstronomy,UniversityofVictoria,Victoria,BCV8P1A1,Canada
Received2009February26;accepted2009December2;published2010January6
ABSTRACT
We present high spectral resolution Very Large Telescope observations of the broad absorption line quasar
SDSS J0318−0600. This high-quality data set allows us to extract accurate ionic column densities and
determine an electron number density of n = 103.3±0.2 cm−3 for the main outflow absorption component.
e
The heavily reddened spectrum of SDSS J0318-0600 requires purely silicate dust with a reddening curve
characteristic of predominately large grains, from which we estimate the bolometric luminosity. We carry out
photoionization modeling to determine the total column density, ionization parameter, and distance of the gas
and find that the photoionization models suggest abundances greater than solar. Due to the uncertainty in the
location of the dust extinction, we arrive at two viable distances for the main ouflow component from the
central source, 6 and 17 kpc, where we consider the 6 kpc location as somewhat more physically plausible.
Assuming the canonical global covering of 20% for the outflow and a distance of 6 kpc, our analysis yields
a mass flux of 120 M(cid:4) yr−1 and a kinetic luminosity that is ∼0.1% of the bolometric luminosity of the
object. Should the dust be part of the outflow, then these values are ∼4× larger. The large mass flux and
kinetic luminosity make this outflow a significant contributor to active galactic nucleus feedback processes.
Keywords: quasars:absorptionlines–quasars:individual(SDSSJ0318-0600)
Online-onlymaterial:colorfigure,figureset,machinereadabletable
de Kool et al. (2001) determined the distance to the outflow
1.INTRODUCTION
observed in FIRST J1044+3656 to within a factor of 100 and
Quasar outflows, seen as ultraviolet blueshifted absorption had a similar uncertainty in the inferred N (see their Table
˙ ˙H
features in their spectra, may contribute to a variety of active 3),whichledtoanuncertaintyinM andE ofapproximately
k
galactic nucleus (AGN) feedback mechanisms (Elvis 2006). 1 order of magnitude. In the cases of FIRST J1214+2803 &
Such feedback processes are invoked to explain the evolution FIRST J0840+3633, de Kool et al. (2002a, 2002b) were able
˙ ˙
of the super massive black hole (SMBH; Silk & Rees 1998; to constrain M and E to a similar accuracy. For the quasar
k ˙ ˙
Blandford&Begelman1999),evolutionofthehostgalaxy(Di 3C 191, Hamann et al. (2001) estimated M and E to within
k
Matteo et al. 2005), shape of the observed quasar luminosity a factor of a few. However, beside their internal uncertainties,
function(Hopkinsetal.2005a;Springeletal.2005;Mencietal. all the works cited above suffered from unquantified system-
2006),andtheenrichmentoftheintra-clusterandinter-galactic aticerrorsduetotheuseofinadequateabsorptionmodelsthat
media(Molletal.2007). led to unreliable measurements of column densities in the ob-
The contribution of quasar outflows to AGN feedback de- servedtroughs,whicharecrucialfordeterminingalmostevery
˙
pends mainly on their mass flux (M) and kinetic luminosity physicalaspectoftheoutflows:theionizationequilibriumand
˙
(E ),bothofwhichdependlinearlyonthetotalhydrogencol- abundances, number density, distance, mass flux, and kinetic
k
umndensity(N )oftheoutflowanditscharacteristicdistance luminosity.
H ˙ ˙
(R) from the central source (see Equations (9) and (11) in InordertodetermineaccurateM andE inquasaroutflows,
k
Section 6). Until recently, only loosely constrained estimates welaunchedamultistageresearchprogram:wefirstdeveloped
have been available for N and R in the same outflow. analysis techniques that allow us to determine reliable trough
H
Morris et al. (1986) and Tripp et al. (1996) were only able columndensities(Aravetal.1999a,1999b,2002,2005,2008;
tofindlowerlimitsforthedistancetooutflowsinGC1556+335 Scottetal.2004b;Gabeletal.2005).Thiswasfollowedbyiden-
andHS1946+7658,respectively.Wampleretal.(1995),analyz- tifyingoutflowtargetsinwhichwecanfinddiagnosticsforboth
ingthespectrumofQSO0059−2735,constrainedthedistance N andR.Wesearchedthrough∼50,000QSOswithz>0.25
H
oftheoutflowtoarangespanningoveranorderofmagnitude. andr<19.3intheSloanDigitalSkySurvey(SDSS)DataRe-
lease 6 (Adelman-McCarthy et al. 2008), ∼100 objects were
foundtoexhibitintrinsicoutflowabsorptionsystemscontaining
∗ BasedonobservationscollectedattheEuropeanOrganizationfor
troughsfromexcitedormetastablelevelsofoneormoreofthe
AstronomicalResearchintheSouthernHemisphere,Chile;underprogram
078.B-0433. followingions:Hei,Siii,Feii,Feiii,orNiii.Thekeyspectral
611
612 DUNNETAL. Vol.709
featurestoobtaindistancesandtotalcolumndensitiesforout- Table1
flowsare(1)absorptiontroughsofexcitedandmetastablelevels VLTObservationsofQSOJ0318−0600
from which we can determine the electron density and (2) the
Date Timea JDb Airmass Seeing
availability of troughs from many ions, including lines from
2006Sep30 04:35:01 54008.19092 1.41 1.08
multiple ions of the same element. We then began observing
2006Oct01 03:51:30 54009.25268 1.12 1.07
these objects with a combination of high spectral resolution,
2006Oct01 06:53:51 54009.28740 1.06 0.97
large spectral coverage, and high signal-to-noise ratios that in 2006Oct15 05:55:23 54023.24679 1.06 1.00
aggregate allows for the use of the analysis techniques men- 2006Oct19 05:34:22 54027.23220 1.07 0.82
tionedabove.Aravetal.(2008)andKoristaetal.(2008)used 2006Oct20 06:49:21 54028.28427 1.07 0.71
thisanalysismethodonVLTobservationsofQSO2359–1241, 2006Oct22 04:45:58 54030.20063 1.10 0.66
derivingN andhydrogennumberdensitydeterminationswith 2006Oct22 05:38:28 54030.23505 1.06 0.55
H
accuraciesbetterthan25%and20%,respectively.
The object analyzed here is SDSS J0318−0600, which was Notes.
aExposuretimeforeachobservationwas2800s.
foundinoursearchthroughtheSDSSdatabase(althoughfirst
bJulianDatepresentedindays+2400000.
discovered by Hall et al. 2002). We chose this object for a
highresolutionfollow-upobservation,duetoitshighapparent
brightness and its suitability for VLT observations. SDSS ∼40,000.Thedatawerereadoutina2×2pixel-binnedfashion,
J0318−0600 is a luminous quasar (log L ≈ 47.7 erg s−1, inhighgainmode.
Bol
see Section 5; z = 1.9668; Hall et al. 2002; Schneider et al. The data were extracted and calibrated using the standard
2003)thatshowsamyriadofoutflowcomponentsrangingfrom UVES data reduction pipeline, based on ECHELLE routines,
ahigh-ionizationbroadabsorptionlinesystemtoseveralnarrow whichispartofthereductionpackageMIDAS(Ballesteretal.
absorptionline(NAL)featuresspanningavelocityrangefrom 2000). This calibration process can introduce quasi-periodic
−2800to−7500kms−1,withrespecttothequasar’srestframe. oscillationsinamplitudeinthefinalspectralproduct(seeArav
InasurveybyHalletal.(2002),itwasclassifiedasanironlow- et al. 2008, on their analysis of QSO 2359−1241), which can
ionizationbroadabsorptionlinesystem(FeLoBAL)andlisted createupto2%–3%systematicerrorsincontinuumplacement.
asanunusualquasarduetotheBALlocatedat∼27,000kms−1 Theobservations werecorrectedtoheliocentric andsubjectto
and the system of NALs, which appears as a BAL in higher a cosmic-ray removal procedure (σ > 3.5). We re-binned the
ionization lines such as Civ. They noted that the Feii UV1, datato7.0kms−1,approximatelyoneresolutionelement,and
UV2,andUV3multipletsweredetectedinabsorptionandthat normalized the spectrum using the methods described in Arav
theUV38multipletappearedtobepresentaswell.Itwasalso etal.(2008).
notedthatSDSSJ0318−0600hasaheavilyreddenedspectrum.
Prochteretal.(2006)listedthisobjectasastrongMgiiabsorber 3.DETECTIONANDMEASUREMENTS
witharest-frameabsorptionwidth>1.4Å,inasearchofMgii
absorbing objects. Herbert-Fort et al. (2006) showed that the The spectrum of SDSS J0318−0600 contains a plethora
object’s absorption was strong, particularly in Siii λ 1808, of absorption features available for potential diagnostics. In
and labeled the absorber as a damped Lyman alpha system. Figure 1, we show a sample of the VLT spectrum with line
However, in our VLT data, we detect absorption from excited identificationsandpresentthefullspectrumwithidentifications
ionic energy levels that conclusively classify the system as an inouronlinefigure.Theseidentificationscomefrommatching
outflow(Hamannetal.1997). theMgiidoubletlinesandplottinglocationidentifiersforother
The outline for this paper is as follows. In Section 2, we ionic lines. We also provide an online table for all identified
present the VLT eschelle observations and their reduction. In lines, their wavelengths, oscillator strengths, and references;
Section3,wediscussourmethodsofdeterminingandmeasuring see Table 2. We show in Figure 1 a portion of the full online
individual kinematic components. We then concentrate on a figure that contains readily visible lines from both the ground
physical analysis of the main component of the outflow: in andexcitedlevelsofFeii(lowerenergylevelsupto1873cm−1).
Section 4, we present our photoionization analysis of the
spectrum and determine the hydrogen column density (N ), 3.1.IdentificationofKinematicComponents
H
electron density (n ), distance (R), and temperature (T) for
e Weidentifyeachoftheindividualkinematicabsorptioncom-
the main absorption component. We derive the mass flux and ponents in the spectrum using the Alii λ1671 absorption line
kineticluminosityinSection5,andinSection6wediscussour
profile, which is a singlet transition with no nearby strong ab-
results.
sorption features. In Figure 2, we show that there are approx-
imately11separatekinematiccomponents(labeleda–k),with
2.OBSERVATIONSANDREDUCTION
componentebeingclearlyablendofmultipleinseparablecom-
During 2006 October, we obtained eight echelle spec- ponents. Using Alii as a template for the absorbers we search
tra, each with an exposure time of 2850 s, of the object otherionicspeciesforeachofthe11components.
SDSS J0318−0600 (z = 1.967, Schneider et al. 2007, R.A. Next,weidentifythebroad,strongicomponentinasmany
03:18:56.7,decl.−06:00:37.4)withtheVLT.Theobservations lines as possible and select unblended troughs from which we
werecarriedoutbyEuropeanSouthernObservatory(ESO)staff are able to measure ionic column densities. Figure 1 shows
and we present the observational parameters in Table 1. The the UV 38 Feii multiplet, which exhibits several absorption
spectra were taken using the UV-Visual Echelle Spectrograph featuresfromcomponenti.Wenotethattheabsorptionfeature
(UVES)withaslitwidthof1.0arcsec,andacentralwavelength at ∼4727 Å is the k component of the Feii λ1608 resonance
positionof5800and3460Åforthered(Grating/Filter=CD1/ line. While this identification scheme is sufficient to locate
HER5)andblue(Grating/Filter=CD3/SHP700)detectorsre- themajorityofthelinesthatshowanicomponent,wealsouse
spectively.Aslitwidthof1.0arcsecgivesaresolvingpowerof theAliiasatemplate(seeSection3.3)tosearchfortheother
No.2,2010 THEMULTI-COMPONENTABSORBERQSO0318-0600 613
Figure1.PortionoftheVLTspectrumshowingtheFeiiUV38multipletinSDSSJ0318−0600(thefullspectrumcanbefoundonline).Lineidentificationsare
indicatedbyverticalbluelinesfortheexpectedpositionofcomponenti,basedontheredshiftz=1.9257.Theredshiftofthequasarisinblacklocatedatthetop
right.Thelog(gf)valuesoftheidentifiedtransitionsareshownabovethespectrum,wheregisthestatisticalweightandfistheoscillatorstrength.Thesizeofthe
verticalbluelineprovidesthevalue,whichcanbereadfromthey-axisscaleatthetopright.Eachidentifierliststheion,wavelength,andlowerenergylevel(in1000
sofcm−1).Thespectrumerrorisplottedinsolidblackbelowthespectrum(≈0.05innormalizedflux)
(Acolorversionandthecompletefigureset[35images]areavailableintheonlinejournal.)
Table2 3.2.ColumnDensityDeterminations
DetectedAbsorptionLinesinQSO0318−0600
Withalistofmeasurableabsorptiontroughs,weextractionic
Ion Wavelength loggf Elow glow Components Referencea columndensities.Webegintheprocessbymeasuringlinesfrom
Measured the strongest component, (i), where we employ three primary
CII 1334.53 −0.619 0 2 a,b–h,k 5 methodsfordeterminingthecolumndensities.Wedescribethree
CII* 1335.71 −0.359 63 4 a,i,k 5 additional methods for column density determination that are
CIV 1548.20 −0.423 0 2 a,b–h,k 5
lessreliableinSection3.3.Weprovidethemeasuredvaluesof
CIV 1550.77 −0.723 0 2 i,k 5
ioniccolumndensitiesaswellasthemethodappliedinTable3.
Ourfirstmethodofmeasuringcolumndensitiesistomodel
Notes.
asetofobservedFeiiresonancelines(e.g.,Figure3)usingan
a(5)Moore(1970,Section3).
inhomogeneous absorption model, where we approximate the
(Thistableisavailableinitsentiretyinamachine-readableformintheonline
journal.Aportionisshownhereforguidanceregardingitsformandcontent.) gasdistributionacrossourlineofsight(LOS)tothebackground
sourcewithapowerlaw(seedeKooletal.2002c;Aravetal.
10 components in the Feii UV 1, 2, & 3 multiplet absorption 2008, especially Figure 4, for a full description). The optical
complexes. depthatagivenvelocitywithintheoutflowisdescribedby
The Feii multiplets UV 1, 2, & 3 are the best candidates to
identify Feii lines from the other 10 components to measure, τv(x)=τmax(v)xa, (1)
because they contain the Feii transitions with the strongest
where x is the spatial dimension in the plane of the sky
oscillator strengths. However, this task proves to be non-
trivial in SDSS J0318−0600. Identifying measurable lines (simplifiedtoonedimensionwithoutlossofgenerality,seeArav
etal.2005),aisthepowerlawdistributionindex,andτ (v)
from a saturated and heavily blended region (see Figure 2) max
isthehighestvalueofτ atagivenvelocity.Wesimultaneously
is difficult, especially when considering the large number of
solve for both τ and a for each velocity resolution element
strongresonanceandexcitedstatelines.Therefore,weattempt max
of the resonance Feii lines and apply this distribution (a) to
to identify as many of the 11 components in the UV 1, 2,
and3multipletsusingtheAliitemplatetosearchforthese11 the excited Feii lines. We then apply the same distribution
dictatedbytheFeiilinestoallionsbecausethisisthesimplest
componentswhereblendingisnotsoprevalent.Weprovidethe
assumptionthatimposesthestrongestconstraints.
fulllistofdetectedions,transitionwavelengths,theiroscillator
Weconvertthemodeledτ tocolumndensityvia(Savage&
strengths, and lower level energies in the online version of v
Sembach1991)
Table2.
Wefindthatforthelowestandhighestvelocitycomponents 1
(k and a), enough measurements or limit determinations are N(v)=3.8×1014 τv(cm−2km−1s), (2)
fλ
availableandthatwecaneffectivelydeterminetheelectronden-
sity(n ),theionizationparameter(U ),andthetotalhydrogen where λ is the wavelength of the line in Å, f is the oscillator
H H
column density (N , see Section 4). Unfortunately, blending strength,andτ istheopticaldepthinvelocityspaceinkms−1,
H v
prevents us from identifying enough measurable troughs for which is integrated over the spatial dimension x. Using
components b–h for proper analysis. We opt for the limiting Equation (2), we compute the column density for each veloc-
casebytakingthesumoftheselattersystems(seeSection3.2). ity element and integrate over the range in velocity, which we
6
1
4
D
U
N
N
E
T
A
L
.
Figure2. MainoutflowtroughsinSDSSJ0318−0600,orderedbywavelength.Weidentifythe11kinematiccomponentsfoundinAliifromhightolowvelocities,whichwelabelathroughk.IntheplotsofFeii
λ2383,λ2396,andλ2600thereareseveralcontaminatelinespresentduetothetelluricAandBbandsaswellasblendingfromotherFeiitroughs(identifiedinonlinefigure).Eachdoubletalsoshowsblendingbetween
components(e.g.,Civ,Mgii).
V
o
l.
7
0
9
No.2,2010 THEMULTI-COMPONENTABSORBERQSO0318-0600 615
Table3
Componenti:MeasuredColumnDensities
Ion EnergyLevel VelocityRange ColumnDensity Uncertaintya Number Methodsb
(Elowcm−2) (kms−1) (×1012cm−2) (×1012cm−2) ofLinesc
Hei 159856 −4600−3716 <90 ··· 1 6
Ci 0 −4600−3716 <37 ··· 1 6
Cii 63 −4600−3714 >19000 ··· 1 4
Civ 0 −4600−3714 29000 3000 1 4
Oi 0 −4551−3896 1900 +−21020000 1 5
Mgi 0 −4600−3716 <2 ··· 1 6
Mgii 0 −4600−3714 3200 400 1 4
Alii 0 −4477−3924 400 40 1 2
Aliii 0 −4610−3833 1560 220 1 3
Siii 0 −4295−4106 7220 720 1 1
Siii 287 −4295−4106 7380 740 1 1
Siiv 0 −4600−3714 5600 1300 1 4
Crii 0 −4295−4106 14.6 1.5 2 1
Mnii 0 −4295−4106 17.5 1.8 1 1
Fei 0 −4600−3714 <3 ··· 1 6
Feii 0 −4295−4106 1275 128 3 1
Feii 385 −4295−4106 294 77 3 1
Feii 668 −4295−4106 64d ··· 2 1
Feii 863 −4295−4106 147d ··· 2 1
Feii 977 −4295−4106 31d ··· 1 1
Feii 1873 −4295−4106 163 16 4 1
Feii 2430 −4295−4106 25 5.4 1 1
Feii 7955 −4295−4106 8.1 0.8 3 1
Coii 3351 −4295−4106 9.4 0.9 1 1
Niii 0 −4295−4106 180 18 3 1
Niii 8394 −4295−4106 64 6.4 3 1
Znii 0 −4295−4106 8.4 0.8 2 1
Notes.
aReflectsthestatisticalerrorsfromlinefitting.Thisdoesnotreflectthereliabilityofthemeasurementmethods,which
haveincreasingsystematicerrorinorderofincreasinglabelnumber(seeSection3.2).
bMethodusedtodeterminecolumndensity,describedbytherespectivelabelnumber:(1)powerlawfitting,(2)velocity-
dependentcoveringfactorfitting,(3)apparentopticaldepthfitting,(4)“wing”fitting,(5)“tip”fitting,(6)upperlimit
basedonthenoisemethod;seeSections3.2and3.3forfulldetails.
cNumberoflinesusedinfitting.Seeonlinetableforspecifictransitioninformation.
dUnreliablemeasurementsduetoweaklines.
blacksaturatedabsorptionatlargedistances(Aravetal.2008;
deKooletal.2002c).InTable3andthroughoutthispaper,we
willrefertothisasmethod1.
Method2istomodeltheFeiiresonancelineswithavelocity-
dependentLOScoveringfactor.TheLOScoveringfactorinthis
case is a geometric step-function distribution (see Figure 4 in
Arav et al. 2008). In other words, a fraction of the extended
sourceiscompletelyobscuredbytheoutflow,whiletherestof
the source is uncovered. We assume that each radial velocity
element has an independent LOS covering factor, which we
again determine using the Feii resonance lines. We solve a
fittingequationforτ (Aravetal.2005),
v
I(v)=1−C(v)+C(v)e−τ(v), (3)
whereIisthenormalizedintensitywithinthetroughandC(v)
is the velocity-dependent LOS covering factor. First, we solve
Figure3.LinefitsforthethreeuncontaminatedFeiiresonancelinesbasedon Equation (3) for C(v) and τ(v) using at least two resonance
thepowerlawmethod.Thedataarepresentedin7kms−1 binswithasolid lines from Feii. We then calculate the velocity-dependent
line(statisticalobservationalerrorbarsforthesedataarealsoshown),while column density using τ(v) in Equation (2) and multiply the
themodelfitisshownbyadottedline.Eachlineiscolorcoordinatedwiththe column density at each velocity by C(v) to obtain the average
wavelengthlocatedatthelowerleftoftheplot.
column density across the LOS. Finally, we compute the total
ionic column density by integrating across the velocity range
justifylaterinthissection.InTable3,wequotethepowerlaw of the trough. This method is comparable in accuracy to
estimationofthecolumndensities(whenavailable)asthisisthe method 1 (Arav et al. 2008), and the column density results
mostaccurateandmostplausiblyphysicalexplanationofnon- areapproximatelythesameasfoundbymethod1.
616 DUNNETAL. Vol.709
Fuhr&Wiese),whiletheweakerλ2281hasareasonablyreliable
oscillatorstrength(rated“B”).However,wefindthatusingthe
oscillator strengths reported by Fuhr & Wiese is problematic.
While the two weaker lines are well fit with these oscillator
strengths, the trough depths relative to λ1622 are unphysical.
Forexample,scalingtheλ1619troughinapparentopticaldepth
by the ratio of oscillator strengths (∼1.8) should be equal to
the apparent optical depth in λ1622 (or larger in the case of
partialcovering);however,thescaledopticaldepthofλ1619is
significantlysmallerthanthatoftheλ1622trough.Thismeans
thatatleastoneoftheoscillatorstrengthscouldbelessreliable
than previously believed. Because of this issue, we quote an
ioniccolumndensityforthe385cm−1 energylevelthatisthe
mean of the fit to the λ1622 line alone and the fit to the two
weaker lines with an uncertainty equal to the range in column
density.
Figure 4. Power law model fits for four lines of metastable Feii (Elow = The other excited state lines from Feii (e.g., arising from
1873 cm−1), we use the exponential a parameter calculated from resonance 668, 863, and 977 cm−1) are also subject to heavy blending
Feii.SimilartoFigure3. in the multiplets, but unlike the resonance and 385 excited
state lines there is not sufficient column density to provide
Thelastofthethreemethods,method3,issimplytheapparent
deep troughs with high signal-to-noise ratio for the weaker
optical depth method (AOD; Savage & Sembach 1991). This
lines.Thus,thecolumndensitymeasurementsfromtheseenergy
methodassumesthatallphotonstravelingtotheobserverpass
levels are significantly more uncertain. The exceptions to this
throughthesameamountofgasatagivenvelocity,whichgives
theequationfornormalizedintensity:I(v) = e−τ(v).Weagain arelinesfromthelowerenergylevelstates1873cm−1(4F)and
7955cm−1(4D).
converttocolumndensityviaEquation(2)andintegratetofind
WefindfiveseparateabsorptiontroughsofFeiiarisingfrom
the total ionic column density. This method does not account
the level at 1873 cm−1, which are shown in Figure 4. We
for partial LOS covering and saturation effects in line centers,
successfullyfittheseusingtheoscillatorstrengthsfromKurucz
whichcanunderestimatecolumndensitiesbyuptoanorderof
& Bell (1995) to determine the column density for this level.
magnitude.However,wefindthatforSDSSJ0318-066,inmost
However,thecompilationofrecommendedoscillatorstrengths
casesaLOScoveringfactorof1(i.e.,theAODapproximation)
of Feii from Fuhr & Wiese (2006) yields values lower than
yieldssimilarN valuesasthosederivedbythepowerlawor
ion ∼0.3dexfortwoofthetransitions,λ1637.4andλ1702.0.For
partial covering method, a point we will discuss later in this
thesetransitionstherecommended valuesarerated“C,”while
section.
no oscillator strengths are given for the other two observed
For the upcoming photoionization modeling, we adopt the
transitions.Inadditiontothedifferenceintheabsolutevalues,
ioniccolumndensitiesasdeterminedbymethod1(powerlaw
there is also a difference in the relative values, and in fact
method)withsomeexceptionstothisduetolineblendingthat
our fits to the absorption troughs in the spectrum favor the
are noted in Table 3. We now present our analysis for the
relative values of Kurucz & Bell (1995). Thus, we opt to use
individualcomponents.
therelativeoscillatorstrengthsfromKurucz&Bell(1995)tofit
3.2.1.MeasurementsofComponenti allfourtroughs,butthelevelcolumndensityderivedthisway
is increased by 0.3 dex, as required by the absolute oscillator
WebeginourcolumndensitydeterminationbyfittingtheFeii
strengthsofFuhr&Wiese(2006).
resonancelinesfromthestrongestcomponent,(i).InFigure3,
We find that the results from all three models (Power law,
weshowthefitsforthreeFeiiresonancelinesusingthepower covering factor, and AOD) are similar for the Feii column
lawmethod.Weselecttheseparticularlinetransitionsbecause
densitymeasurementsofcomponenti,whichsuggeststhatthe
theyprovideuswitharangeofoscillatorstrengthsandarefreeof
LOScoveringfactorofthesystemiscloseto1.Furtherevidence
blendingortelluriccontamination.Usingtheselines,wederive foraLOScoveringfactor≈1caseisshowninFigure5,where
velocity-dependent column densities that we integrate for the weshowthatwecanusetheAliitemplatetofittheAliiidoublet.
totalioniccolumndensity. WescaletwoAliitemplates (oneforAliiiλ1855 and one for
Unfortunately, all strong Feii lines from the lower energy Aliiiλ1863)inτspaceforeachindividualkinematiccomponent
level 385 cm−1 are heavily blended in the UV 1, 2, or 3
fortheblueandtheredlineofthedoubletbytheexpectedratio
multipletswithlinesfromboththeresonanceandotherexcited
of2:1andcoaddthetemplatestogenerateafittothedata.There
lines (e.g., Feii* λ2396, shown in Figure 2), which renders
existonlysmalldeviations,andtheoverallfittothedoubletis
columndensitymeasurementsbasedonthesetransitionstohave
good. The most obvious and important deviation is in the fit
largesystematicerrors.However,wefindrelativelystronglines
to the λ1863 i component, which is due to some saturation in
outsideoftheUV1,2,or3multipletsforthe385cm−1energy the core of the Alii template. This demonstrates that AOD is
state that are useful such as the Feii line λ1622 from the UV
anadequateapproximationandtheLOScoveringfactorforall
38 multiplet. We also find two weaker lines from this energy
components is approximately 1.0. This same procedure gives
state at λ1619 and λ2281 that are unblended. The oscillator similarresultswhenappliedtotheMgiidoubletaswell.
strength values for these three lines are taken from Fuhr &
Wiese(2006).Ofthethreelines,boththeλ1618andλ1622are
reportedtohaveaccurateoscillatorstrengths(ratedas“A”8 by
uncertaintieslessthan3%,10%,and25%,respectively,accordingtotheNIST
8 Accuraciesof“A,”“B,”and“C”areappliedtooscillatorstrengthswith AtomicSpectraDatabase.
No.2,2010 THEMULTI-COMPONENTABSORBERQSO0318-0600 617
Figure5.Aliiidoubletplottedinvelocityspacewithrespecttothebluemember
ofthedoublet.Theblueandredtickmarksandlettersindicatethecomponent
positionsoftheAliiidoubletmembers,Aliiiλλ1855,1863respectively.The
dottedblueandredlinesaretheindividualAliitemplatefitsforeachmember
ofthedoublet(correspondingtotheblueandredtickmarks).Eachindividual
componentisscaledinτ,andtheresultingtemplatesmatchtheexpecteddoublet
ratioof2:1foreachofthecomponents.Wecoadd,inτ space,thetwoAlii
templatesandpresenttheresultingfitingreen.Thefitagreeswiththedatawith
theexceptionoftheλ1863componenti,whichislikelyduetosaturationinthe
λ1855counterpart.
Figure 7.Top left panel shows the Siii λ1527 icomponent. Theremaining
panelsshowtheagreementoftheSiiiλ1527icomponenttroughwiththered
doubletmemberoffiveotherions.TheSiiiλ1527datahavebeenconvertedto
τ(v),whereτ(v)=−ln(I(v)),andscaledbyasinglefactorforeachoftheother
linesinordertoproducethefits(redhistograms)forthesetroughs(datashown
inblack).SomediscrepancybetweentheSiiiλ1527lineandAliiiλ1863occurs
near4000kms−1,whichisduetocontaminationfromthebluekcomponent.
Theseagreementsshowthattheratioofcolumndensitiesbetweeneachionand
Siiiisconstantacrosstheprofilesofthedifferenttroughs.
working with each velocity resolution element separately (see
Aravetal.2008);(2)thatthetroughsofdifferentionscorrespond
tothesameoutflowinggas,whichisanecessaryconditionfor
usingthesemeasurementsinthesamephotoionizationmodels.
Bothassumptionscanbecheckedusingthedataathand.
The first assumption can be tested by checking whether the
ratioofmeasuredcolumndensitiesamongdifferentlowerlevels
ofthesameionvaryasafunctionofvelocity.InFigure6,we
plot the ratios of column densities between those arising from
excited levels to those from the ground state level of Feii and
Figure6.ComponenticolumndensityratiosofFeii*/FeiiandSiii*/Siii,top Siii.Withintheuncertainties,theratiosacrossthetroughsare
andbottomrespectively,invelocityspace.Withintheerrorbarstheratiosare
velocityindependent,showingthattheelectronnumberdensity
constantacrosstheintegrationrange.Thisindicatesthattheoutflowinggashas
aconstantelectronnumberdensityacrossthetrough,whichstronglysuggests isconstantacrosstheflow(seeSection4forelaboration).This
similarionizationconditionsacrossthevelocityspanofthisoutflowcomponent. resultgivesvaliditytoourfirstassumptionandjustifiestheuseof
integratedcolumndensitiesforcomponenti.Wealsotestedthis
3.2.2.ThePhysicalConnectionBetweenMaterialSeenin
for Niii/Niii* and combinations between Niii, Siii, and Feii
DifferentTroughs
resonances and excited lines and find that the ratio is constant
Ultimately,wewanttoestablishthephysicalcharacteristics in all cases. This constant ratio is also seen in the results for
of the outflow based on the column density determinations theoutflowsysteminQSO2359−1241asdescribedbyKorista
described above. In order to do so, we use the integrated etal.(2008).
column densities as input to photoionization models, which Inordertovalidatethesecondassumption,weneedtocheck
in turn determine the total hydrogen column density and thecolumndensityratioacrosstroughsfromdifferentionsand
numberdensityintheoutflow.Thisproceduredependsontwo especiallytocomparelow-andhigh-ionizationtroughs.Todo
assumptions:(1)thatthephysicalconditionsdonotchangeasa so, we use the τ(v) profile of Siii λ1527 and attempt to fit
function of velocity across a given trough. This assumption theprofilesofothertroughswhileusingasingle-scalefactorfor
allow for the use of integrated column densities instead of eachline.TheresultsareshowninFigure7.Itisevidentthatthe
618 DUNNETAL. Vol.709
Figure8.FitstotheAliii,Mgii,Civ,andSiivdoubletswiththecompositeSiiitemplateforcomponentiandtheAliitemplateforallothercomponents.Weadd
twotemplatesinasimilarfashionasforFigure5.Thesefits,however,arescaledbyoneconstantforthebluetemplateandscaledby2:1fortheredtemplate.Wealso
includetheSiiiλ1527resonancelineandλ1533excitedlineinthefitforCiv,whichaffectvelocitiesgreaterthan∼−5500.Thesefourfitsclearlydemonstratethat
foreachion,all11componentsarepresent,andthatnounexplainedcomponentsappear.WenotethatintheCivfitthereisevidenceforacomponentat−3600kms−1
withalargeopticaldepthwhereastheopticaldepthofthiscomponentAliiappearstobesignificantlylower,thusthetemplatefitispoor.Thefitswouldimproveby
scalingeachcomponentbyadifferentfactorinopticaldepth.
scaledτ(v)profileofSiiiλ1527fitsthetroughsofSiiv,Alii, unblended.Thus,wemeasurethecolumndensitiesbasedona
AliiitroughsandMgiiremarkablywell,lendingstrongsupport LOScoveringfactorof1.Wefurtherconfirmthisassumptionof
fortheassumptionthatwearemeasuringthesameoutflowing aLOScoveringfactorof1,aswiththeicomponent,bychecking
gas.ForCiv,whichisthehighestionizationlineobserved,the thattheλ1608linescaleswelltotheunblendedportionofFeii
fitforthecenterofthetroughislessconclusivesincethetrough λ2383 according to oscillator strength. Component a has no
ishighlysaturatedatitscore.However,wepointoutthatthefit measurable Feii resonance lines. However, according to the
tothelow-velocitywing(−3950to−3850kms−1)isverygood, Aliii doublet (Figure 5), we find that a LOS covering of ∼1
whichwouldbeacoincidentunlesstheCivtroughcanbefitted holdsforallcomponentsandweareabletoresorttotheAOD
withthesameτ(v)profileofSiiiλ1527.Insummary,thedata method for our measurements. The results for components k
supportthetwomainassumptionsthatweneedinordertouse andaareshowninTables4and5,respectively.
allintegratedcolumndensitiesinourphotoionizationmodels. Duetothelackofmeasurable,unblendedtroughsforcompo-
Todemonstratethetiebetweenthehigh-andlow-ionization nentsbthroughh,weusetheapparentopticaldepthmethodand
troughsfortheotheroutflowcomponents,weshowinFigure8 integratethetotalcolumndensityacrossthecombinedblended
thatthecombinationoftheSiiicompositetemplate(described troughsforcomponentsbthroughh,−7150to−4600kms−1
in Section 3.3 for component i) and the Alii template (for all invelocity,fortheSiiv,Civ,Mgii,andAliiidoubletsaswell
othercomponents)canbeusedtorecreatethedoublettroughs as the resonance and excited lines of Cii (λ1335, λ1336) and
ofMgii,Aliii,Siiv,andCiv.SimilartoFigure5,weaddtwo Siii(λ1527,λ1533).WepresenttheseresultsinTable6.
templates together in τ(v). We scale the entire blue template
(all11components)byonefactorandscaletherespectivered 3.3.EstimatesandLimits
templateby2:1inτ(v).Thismethodgivesthefewestpossible
For situations where blending between components in dou-
constraintsforthefit.Wefindthatall11kinematiccomponents blets is prevalent (i.e., Civ, Siiv, Cii, and Cii*) or where the
are present in both low- and high-ionization troughs and that trough is heavily saturated (i.e., Civ), our primary method of
there are no unexplained kinematic components in the higher
column density extraction fails. Thus, we resort to other, less
ionization state lines, which is indication that this is the same
accurate, methods to estimate the column densities, which are
outflowing gas for both the high- and low-ionization troughs.
important when constraining photoionization models. We de-
We also note that these fits could be better if we scaled each
velop three additional methods in order to estimate column
individual component for the blue member and kept the 2:1
densities in blended regions, which we explain here in order
ratiotothered,aswedidfortheAliiifitinFigure5.
ofdecreasingaccuracy.
Inthefirstofourestimationmethods(4),weopttoemploy
3.2.3.MeasurementsoftheOtherComponents
atemplatetomapoutapproximateprofilesforthetroughs.We
The other two components with a sufficient number of utilize two templates for this process. The first template is a
measurable absorption lines are the k and a components. fittotheAliiλ1671lineforall11components.However,due
However, we are unable to utilize methods 1 or 2 due to a tomoderatesaturationinthecoreoftheAliiicomponent,we
lack of unblended Feii resonance lines. For component k, create a composite template using the Siii resonance lines for
only one Feii resonance line (Feii λ1608) is measurable and theicomponent.
No.2,2010 THEMULTI-COMPONENTABSORBERQSO0318-0600 619
Table4
Componentk:MeasuredColumnDensities
Element EnergyLevel VelocityRange ColumnDensity Uncertainty Number Methodsb
(Elowcm−2) (kms−1) (×1012cm−2) (×1012cm−2) ofLinesa
Cii 0 −3088−2249 1100 200 1 4
Cii 63 −3088−2249 1950 300 1 4
Civ 0 −2893−2641 1297 130 2 3
Mgii 0 −2893−2641 192 20 1 3
Alii 0 −3047−2494 35 4 1 3
Aliii 0 −3047−2494 73 7 1 3
Siii 0 −3321−2262 640 150 1 6
Siii 287 −2893−2641 352 40 1 3
Siiv 0 −2893−2641 140 20 1 3
Feii 0 −2893−2641 154 20 1 3
Feii 668 −2893−2641 9.0 1.0 1 3
Niii 0 −3199−2502 <120 ··· 1 6
Niii 8394 −2893−2641 10.0 1.0 1 3
Notes.
aNumberoflinesusedinfitting.Seeonlinetableforspecifictransitioninformation.
bMethodusedtodeterminecolumndensity,describedbytherespectivelabelnumber:(1)powerlawfitting,(2)velocity-
dependentcoveringfactorfitting,(3)apparentopticaldepthfitting,(4)“wing”fitting,(5)“tip”fitting,(6)upperlimit
basedonthenoisemethod.
Table5
Componenta:MeasuredColumnDensities
Element EnergyLevel VelocityRange ColumnDensity Uncertainty Number Methodsb
(Elowcm−2) (kms−1) (×1012cm−2) (×1012cm−2) ofLinesa
Cii 0 −7523−7271 333 30 1 3
Cii 63 −7523−7271 577 60 1 3
Civ 0 −7558−7243 734 70 1 3
Mgii 0 −7523−7271 28.7 2.9 1 3
Alii 0 −7523−7271 11.6 1.2 1 3
Aliii 0 −7523−7271 46.0 5.0 1 3
Siii 0 −7523−7271 101 10 1 3
Siii 287 −7523−7271 <50c ··· 1 5
Siiv 0 −7523−7271 145 20 1 3
Feii 0 −7695−7300 <40 ··· 1 6
Notes.
aNumberoflinesusedinfitting.Seeonlinetableforspecifictransitioninformation.
bMethodusedtodeterminecolumndensity,describedbytherespectivelabelnumber:(1)powerlawfitting,(2)velocity-
dependentcoveringfactorfitting,(3)apparentopticaldepthfitting,(4)“wing”fitting,(5)“tip”fitting,(6)upperlimit
basedonthenoisemethod.
cColumnlimitbasedonthelimitingratio“tip”fitforSiii*/Siii.
Table6 thecoreofthistroughisnotsaturated;however,thewingsare
Componentsb–h:ColumnDensitiesLimits buried in the noise. We therefore create a composite template
using the AOD column densities of the λ1527 for the wings
Element EnergyLevel VelocityRange ColumnDensity Number
(Elowcm−2) (kms−1) (×1012cm−2) ofLinesa A(−O3D82c0otloum–3n9d9e0nksimtiess−o1fanthde–λ41389008tolin–e45f8o0r tkhme cso−r1e),(a−n4d3t9h0e
CCiivi 00 −−67915500−−44460000 >>193900000 11 and−3990kms−1).WethenconverttheresultantSiiicolumn
Mgii 0 −7150−4600 >910 1 densityprofiletoτ(v)templatefortheλ1527line.
Alii 0 −7150−4600 >440 1 To measure column densities, we scale this composite τ(v)
Aliii 0 −7150−4600 >840 1 template to match the red wings of the Mgii, Siiv, and Civ
Siii 0 −7150−4600 >3200 1 doubletsaswellasCii*,whichareapparentlyfreeofblending.
Siiv 0 −7150−4600 >1900 1 Weassumethatthecolumndensityratioisconstantacrossthe
Feii 0 −7150−4600 >600 1 troughs, which is supported by Figure 7, scale the composite
template for the i component to match and then integrate the
Note.aNumberoflinesusedinfitting.Seeonlinetableforspecifictransition total column (assuming a C ≈ 1) from the template. We
los
information.
refer to this method as the “wing” fitting method (method 4).
Theerrorestimationisprovidedbyusingtwoτ scalingvalues,
Tocreatethistemplate,weuseboththeSiiiλ1808andλ1527
one underestimating and one overestimating the noise level in
lines.Theλ1527lineissimilarinshapetotheAliiλ1671line,
the trough’s wing. We note that these measurements use only
andwhilethecoreismoderatelysaturated,itprovidesuswith
oneline,thereddoubletmember,whichisreflectedinTables3
a good fit to the wings of the trough. In contrast, the λ1808
through 6. To further test the validity of this method, we used
linehasasignificantlyweakeroscillatorstrengthandtherefore the composite template to fit the wing of the Siii λ1527 line
620 DUNNETAL. Vol.709
and we find that the template is able to reproduce the column Inaddition,wemeasureupperlimitstothecolumndensitiesof
density we find in our power law fitting of the λ1808 line to Hei*, Fei, Ci, and Mgi. As already shown, a similar absorp-
within10%. tion trough structure is shared by the strongest transitions of
The next method we designate as the “tip” fitting method, thesinglyionizedspecies,andthoseofintermediateionization
or method 5, where we estimate the column densities in a (Aliii and Si IV), as well as C IV. Additionally, component i
similarwaytomethod4.Forexample,weestimatethecolumn likelyhasthelargestcolumndensityofanycomponentinSDSS
densityofOiλ1302fortheicomponentintheregioncontaining J0318−0600,giventhatithasthelargestnumberofabsorption
blended lines from Siii λ1304 and Siii* λ1309. We find that lineidentificationsandisthedeepestabsorptionfeaturefortran-
thecompositetemplatefitfortheicomponentagreeswellwith sitionsoflowoscillatorstrengthsand/orlowrelativeelemental
thedeeptroughat∼3809Åinvelocityspace(showninonline abundance.Therefore,weanalyzecomponentihere,andanal-
Figure1),whichappearstobethetipofOiabsorption.Thus,we ysis of all other absorption components will be presented in a
use the composite Siii template to approximate the minimum subsequentpaper(M.Bautistaetal.2010,inpreparation).
andmaximumamountofcolumndensitythatcouldcomefrom One of the main objectives of modeling the observed ionic
Oi.Duetotheuncertaintyincontinuumplacementandpossible column densities is the determination of the total hydrogen
saturation, we consider this method less accurate than method column density of the outflow N and its distance from the
H
4,whichisreflectedinthelargererrorbars. centralsourceR,whicharekeyinthedeterminationofkinetic
Ourlastcolumndensityestimationmethod(thenoisemethod luminosityoftheoutflow(seeSection6).Theformerisobtained
ormethod6)definesupperlimitsonthecolumndensityofions directly through photoionization modeling, but the latter is
based on the statistical error of the data. Because the column not.Instead,modelingyieldstheso-calledionizationparameter
density of Hei is important for photoionization models (see definedas
Q Φ
Aravetal.2001;Koristaetal.2008),weestimateanupperlimit U = H = H, (4)
for the column density of the excited 23s level of Hei (Hei* H 4πR2n c n c
H H
hereafter)incomponentiforHei*λ3189.Todothis,wescale
where n is the total hydrogen density, c is the speed of light,
the Siii template for the i component and compare it to the Φ is thHe surface flux of ionizing photons, Q is the rate of
H H
regionwherethelinewouldbedetected.Wevarythescalingto
hydrogenionizingphotonsemittedbythecentralobject,which
thenoiselevel,findthelargestpossibleopticaldepththatcould
isdefinedby
beburiedwithoutdetectionandintegrateacrossthetemplateto (cid:2)
determinethecolumndensity.Wealsoperformthisanalysisfor ∞ L
Mgiλ2853,Feiλ2484,andCiλ1560andquotethemeasured QH = νdν(ionizingphotonss−1), (5)
hν
1Ry
limitsinTable3.
Component k presents its own problems. Unlike the i com- wheretheintegrationrangecoverstherangeofionizingphotons,
ponent, here we effectively measure column densities for Feii L is the luminosity at each frequency, and h is the Planck
ν
resonance and excited levels (E = 0 cm−1 to E = 668 cm−1), constant.Fromthisdefinition,Q canbeestimateddirectlyfrom
H
but we lack a Siii resonance line to provide a ratio to the Siii theobservedluminosity(λL oftheobjectandsomeknowledge
λ
λ1309excitedline.Therefore,weapplymethod5withtheAlii of its spectral energy distribution (SED), see Sections 4.2 and
templatetofindlimitsontheSiii.Moreover,weusethe“wing” 4.3).Thus, the distance Rcan be obtained fromthe diagnosed
fittingmethod(method4)withthesameAliitemplatetoesti- value of U whenever one has an independent determination
H
matethecolumndensityforCiiandCii*incomponentk. ofn ,whichinacloudwithfullyionizedhydrogenisroughly
H
In component a, the number of measurable lines is even equaltotheelectrondensity,n .
e
fewerthanforcomponentk.Theonlyclean,unblendeddensity Thus, the first step in the analysis is to determine n from
e
diagnosticisCiitoCii*.Asthecriticaldensityforthisratiois its effect via collisions on the relative populations of excited
low(∼102cm−3,Blum&Pradhan1992;FroeseFischer1983), levelsobservedinthespectrum.Later,wediscussthenatureof
it is important to find another density check. Thus, using the theSED,whichistobeusedinthedeterminationofQandas
Aliitemplate,weestimateanupperlimittothecolumndensity inputforphotoionizationmodeling.Afterthis,wewillproceed
ratioofSiii*toSiiitobe0.49forcomponenta. todetailedphotoionizationmodeling.
3.4.SystematicUncertainty 4.1.ElectronDensityDetermination
We recognize that there exist systematic errors that could Underexcitationequilibriumconditions,thecolumndensities
contribute further to the uncertainty in our measurements. For of lowly excited metastable levels can be used as diagnostics
example,ourplacementofthecontinuum,definedinSection2, of electron density, assuming that the atomic parameters and
could result in increased errors of the Siii λ1808 and Siii* excitation processes responsible for excitation are sufficiently
λ1817columndensitiesby5%.Theamountofsaturationinthe well understood. We have measured column densities for the
coreofSiivisanothersystematicerrorthatcouldbeapotential 0 cm−1 ground state and low-lying metastable excited levels
source of error in column density, which at maximum, could withinSiii,Feii,andNiii.
lead toan error inan ionization parameter of 0.1dex. Both of Thesimplestandprobablymostreliableoftheelectronden-
these are negligible compared to the uncertainties due to the sity diagnostics is that from the ratio of the column densities
chemicalabundancechoice. of the Siii levels, as shown in Figure 9. Here, the ratio of the
excited 3s23p 2Po at 287 cm−1 to the 3s23p 2Po ground
3/2 1/2
level is calculated from three different sets of effective colli-
4.SPECTRALDIAGNOSTICSANDMODELING
sion strengths, Dufton & Kingston (1991), Tayal (2008), and
The observed spectrum of SDSS J0318−0600 exhibits dis- M.Bautistaetal.(2010,inpreparation).Wemeasurethiscol-
tinct absorption from Cii and Civ, Oi, Mgii, Alii and Aliii, umndensityratiofromthepairofabsorptionlinesat1808.0Å
SiiiandSiiv,Crii,Feii,Coii,Niii,andZniiforcomponenti. (resonant) and 1816.9 Å (excited state). As described above,