Galactic Winds with MUSE: A Direct Detection of FeII* Emission from a z = 1.29 Galaxy

1.7 MB·

by  Hayley Finley

Astronomy&Astrophysicsmanuscriptno.FeII (cid:13)cESO2017
January30,2017
ii
Galactic Winds with MUSE: A Direct Detection of Fe * Emission
from a z = 1.29 Galaxy (cid:63)
HayleyFinley1,2,NicolasBouché3,ThierryContini1,2,BenoîtEpinat1,2,4,RolandBacon5,JarleBrinchmann6,7,
SebastianoCantalupo8,SantiagoErroz-Ferrer8,RaffaellaAnnaMarino8,MichaelMaseda6,JohanRichard5,Anne
Verhamme5,9,PeterM.Weilbacher10,MartinWendt10,11,andLutzWisotzki10
1 UniversitédeToulouse,UPS-OMP,31400Toulouse,Francee-mail:[email protected]
2 IRAP,InstitutdeRechercheenAstrophysiqueetPlanétologie,CNRS,14avenueÉdouardBelin,31400Toulouse,France
3 IRAP,InstitutdeRechercheenAstrophysiqueetPlanétologie,CNRS,9avenueColonelRoche,31400Toulouse,France
7 4 AixMarseilleUniv,CNRS,LAM,Laboratoired’AstrophysiquedeMarseille,Marseille,France
1 5 CRAL,ObservatoiredeLyon,CNRS,UniversitéLyon1,9AvenueCh.André,F-69561SaintGenisLavalCedex,France
0 6 LeidenObservatory,LeidenUniversity,P.O.Box9513,2300RALeiden,TheNetherlands
2 7 InstitutodeAstrofísicaeCiênciasdoEspaço,UniversidadedoPorto,CAUP,RuadasEstrelas,PT4150-762Porto,Portugal
8 ETHZurich,InstituteofAstronomy,Wolfgang-Pauli-Str.27,CH-8093Zürich,Switzerland
n 9 ObservatoiredeGenève,UniversitédeGenève,51Ch.desMaillettes,1290Versoix,Switzerland
a 10 Leibniz-InstitutfürAstrophysikPotsdam(AIP),AnderSternwarte16,D-14482Potsdam,Germany
J 11 InstitutfürPhysikundAstronomie,UniversitätPotsdam,Karl-Liebknecht-Str.24/25,14476Golm,Germany

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ABSTRACT
]
A
Emissionsignaturesfromgalacticwindsprovideanopportunitytodirectlymaptheoutflowinggas,butthisistraditionallychallenging
G
becauseofthelowsurfacebrightness.Usingverydeepobservations(27hours)oftheHubbleDeepFieldSouthwiththeMultiUnit
. SpectroscopicExplorer(MUSE)instrument,weidentifysignaturesofanoutflowinbothemissionandabsorptionfromaspatially
h resolvedgalaxyatz=1.29withastellarmassM =8×109M ,starformationrateSFR=77+40M yr−1,andstarformationrate
p (cid:63) (cid:12) −25 (cid:12)
- surfacebrightnessΣSFR=1.6M(cid:12)kpc−2withinthe[Oii]λλ3727,3729half-lightradiusR1/2,[Oii]=2.76±0.17kpc.Fromacomponent
o ofthestrongresonantMgiiandFeiiabsorptionsat−350kms−1,weinferamassoutflowratethatiscomparabletothestarformation
r rate. We detect non-resonant Feii* emission, at λ2626, λ2612, λ2396, and λ2365, at 1.2−2.4−1.5−2.7×10−18 egs s−1 cm−2
st respectively.Thesefluxratiosareconsistentwiththeexpectationsforopticallythickgas.Bycombiningthefournon-resonantFeii*
a emissionlines,wespatiallymaptheFeii*emissionfromanindividualgalaxyforthefirsttime.TheFeii*emissionhasanelliptical
[ imso5r0p%hollaorggyerthtahtainstrhoeugsthellylaarlicgonnetdinwuuitmht(hRegalax(cid:39)y2m.3i4no±r0k.i1n7em)oartitchaex[iOs,iai]ndneibtsuilnatrelginraet.eMdhoarlefo-lviegrh,tthraedFiuesi,i*R1e/m2,Fiessii∗io=n4sh.1o±w0s.a4bklpuce,
1 1/2,(cid:63)
wingextendingupto−400kms−1,whichismorepronouncedalongthegalaxyminorkinematicaxisandrevealsaC-shapedpattern
v
inap−vdiagramalongthataxis.Thesefeaturesareconsistentwithabi-conicaloutflow.
3
4 Keywords. Galaxies:evolution–Galaxies:starburst–Galaxies:ISM–ISM:jetsandoutflows–Ultraviolet:ISM
8
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1. Introduction binetal.2010b,2014;Martinetal.2012;Heckmanetal.2015;
.
1 Zhuetal.2015;Chisholmetal.2015),observationalconstraints
0Galactic winds, driven by the collective effect of hot stars and for the physical properties of galactic outflows, including their
7supernovae explosions, play a major role in regulating galaxy
extentsandmassoutflowrates,aresparse.Traditional"downthe
1evolution.Byexpellingenrichedmatterbeyondthehalo,galac-
barrel" 1D galaxy spectroscopy provides direct constraints on
:tic winds can address discrepancies between observations and
v the wind speed from the blue-shifted absorption lines but can-
iΛCDMmodelsthatover-predictthenumberoflow-massgalax- not constrain the physical extent of outflows, leading to large
Xies (Silk & Mamon 2012) and enrich the intergalactic medium
uncertaintiesinoutflowrates.Techniquesthatuseabackground
r(Oppenheimer & Davé 2008; Ford et al. 2016). Likewise, sourcecanaddressthisquestion.
a
galactic winds may play a major role in regulating the mass-
Forinstance,thebackgroundquasartechniqueprovidescon-
metallicity relation (Finlator & Davé 2008; Lilly et al. 2013;
straintsonthephysicalextentofgasflowsfromtheimpactpa-
Tremontietal.2004).Therefore,quantifyingthemassfluxesof
rameterbetweenthegalaxyandtheabsorbinggas(e.g.Bouché
galacticoutflows(andtheirextents)isnecessarytogainacom-
et al. 2012; Kacprzak et al. 2012; Schroetter et al. 2015, 2016;
pleteunderstandingofgalaxyevolution.
Pérouxetal.2016;Bouchéetal.2016;Strakaetal.2016).These
However, while galactic winds appear ubiquitous (e.g.,
recentstudieshavemadeprogressinvestigatingthekinematics,
Veilleuxetal.2005;Weineretal.2009;Steideletal.2010;Ru-
orientation,andextentofgasflowsaroundstarforminggalaxies.
(cid:63) BasedonobservationsoftheHubbleDeepFieldSouthmadewith As a variation on this technique, spectroscopy against a back-
ESOtelescopesattheLaSillaParanalObservatoryunderprogramID ground galaxy probes absorption from the foreground galaxy
60.A-9100(C). Advanced data products are available at http://muse- halooveralargersolidangle(e.g.,Adelbergeretal.2005;Ru-
vlt.eu/science. binetal.2010a;Steideletal.2010;Bordoloietal.2011,2014;
Articlenumber,page1of13
A&Aproofs:manuscriptno.FeII
Diamond-Stanicetal.2016).However,theseconstraintsonthe emissiontypicallyrequiresstackinghundredsofgalaxyspectra.
physicalextentofoutflowsareusuallylimitedduetotheirone- Using more than 800 Lyman break galaxies (LBGs) at z > 2,
dimensional nature, except for Cazzoli et al. (2016). Mapping Shapleyetal.(2003)firstdetectedSiii*inthecompositespec-
the extent of gas flows in two dimensions is critical to better trum, and Berry et al. (2012) more recently detected Cii* and
constrainmassoutflowrates. Siii* in the composite spectrum of 59 LBGs. Since the non-
Mappingoutflowsinemission,suchasforM82(e.g.,Shop- resonant Feii* lines are at redder wavelengths than Cii* and
bell & Bland-Hawthorn 1998; Lehnert et al. 1999) and other Siii*, they are practical for investigating outflows at lower red-
nearby galaxies (e.g., Heckman et al. 1995; Cecil et al. 2001; shifts, like z ∼ 1. Based on comparing composite spectra from
Veilleux&Rupke2002;Matsubayashietal.2009;Moiseevetal. samples of ∼ 100 or more star-forming galaxies at z ∼ 1 − 2
2010), is difficult at high redshift, because the emitting gas in- (Erb et al. 2012; Kornei et al. 2013; Tang et al. 2014), Feii*
herently has a very low surface brightness. Beyond the local emissionmayvarywithgalaxyproperties,suchasgalaxymass
universe, galaxies with emission signatures from outflows are anddustattenuation.Coiletal.(2011)presentindividualspec-
beginning to be detected. Currently, rest-frame UV and optical tra with different combinations of blue-shifted absorption, res-
spectroscopy use three types of emission signatures to map the onant Mgii emission, and non-resonant Feii*. In two notable
extentofoutflows:thenebular,resonant,andnon-resonantemis- direct detections of Feii* emission from galaxies at z = 0.694
sionlines.ThemostcommonnebularemissionlinesseeninHii andz = 0.9392(Rubinetal.2011;Martinetal.2012),thenon-
regionsarehydrogenrecombinationandforbiddenlines,suchas resonantemissionisobservedalongwithblue-shiftedabsorption
[Oii]λλ3727,3729. A transition is resonant when a photon can lines and resonant Mgii emission, allowing the authors to con-
be absorbed from the ground state and re-emitted to the same strain and model the outflows. Similarly, Jaskot & Oey (2014)
lowestlevelofthegroundstate,asforLyman-alphaandtheMgii usenon-resonantCii*andSiii*emissioninUVspectraoffour
λλ2796,2803transitions.Atransitionisnon-resonantwhenthe greenpeagalaxiesatz∼0.14−0.2toinferthegeometryoftheir
photoncanbere-emittedtoanexcitedlevelofagroundstatethat outflows.
has multiple levels due to fine structure splitting. Non-resonant These studies provide information about outflow properties
transitionsarecommonlydenotedwitha*,likeFeii*.Duetothe on galactic scales, but it is also possible to characterize out-
slight energy difference between the ground and excited states, flows from individual star-forming regions across z > 1 galax-
photonsfromnon-resonantemissionnolongerhavethecorrect ies thanks to adaptive optics or gravitational lensing (i.e., Gen-
wavelength to be re-absorbed through a resonant transition and zeletal.2011;Rigbyetal.2014;Karmanetal.2016;Bordoloi
instead escape. In other words, the gas is optically thin to pho- etal.2016,Patricioetal.inprep.).Usingadaptiveoptics,Gen-
tonsthatareemittedthroughanon-resonanttransition. zeletal.(2011)identifystar-formingregionsinfivez>2galax-
Thefirsttypeofemissionsignature(nebularlines)fromout- iesandarguethatbrightregions(orclumps)withabroadcom-
flowscanappearasabroadcomponentinnebularemissionlines ponent in the nebular emission are the launch sites for massive
such as Hα. Such broad component is regularly seen in local galacticwinds.Withthebenefitofgravitationallensing,Karman
Ultra-LuminousInfra-RedGalaxies(ULIRGs,e.g.Soto&Mar- et al. (2016) characterize Mgii emission, Feii*λλ2612,2626
tin 2012; Arribas et al. 2014; García-Burillo et al. 2015) and emission, and Feii absorption from multiple star-forming re-
morerecentlyinnormalstar-forminggalaxies(Woodetal.2015; gions across a supernova host galaxy at z = 1.49 at locations
Ciconeetal.2016).Athighredshifts,Newmanetal.(2012)de- both associated with and independent of the supernovae explo-
tectedabroadHαcomponentincompositespectraofz∼2star- sion.Bordoloietal.(2016)likewisedetectblueshiftedFeiiand
forming galaxies and Genzel et al. (2011) observed this broad Mgii absorptions, redshifted Mgii emission, and non-resonant
component in a few individual galaxies. Newman et al. (2012) Feii*λλ2612,2626 emission in four star-forming regions of a
found that the broad emission is spatially extended beyond the gravitationally lensed galaxy at z = 1.70, but find that the out-
half-lightradius,R . flow properties vary from region to region. Spatially resolved
1/2
The second possible emission signature of outflows comes observations suggest that outflow properties could be localized
from resonant transitions such as Lyα, a line which is often andstronglyinfluencedbytheneareststar-formingclump.
more extended than the stellar continuum (e.g. Steidel et al. Despiteadvancesfromthesediversestudies,wehavenotyet
2011; Matsuda et al. 2012; Wisotzki et al. 2016) but might be been able to map the morphology and extent of outflows from
strongly affected by dust absorption. Emission from resonant individual galaxies beyond the local universe. The new genera-
metal lines, such as Siii, Feii, or Mgii, is less affected by dust tionofintegralfieldspectrographs,theMultiUnitSpectroscopic
and may be observed as P-cygni profiles. The relative strength Explorer(MUSE;Baconet al.2015)ontheVLTandthe Keck
between the (mostly) blueshifted absorption and (mostly) red- CosmicWebImager(Morrisseyetal.2012),arewell-suitedfor
shiftedemissiondictateswhetherthesignatureappearsasatra- studyinggalacticwindsinemissionandtacklingthischallenge.
ditional P-cygni profile or as emission ‘infilling’. Contrary to While slit spectroscopy can inadvertently miss scattered emis-
the resonant Feii lines observed across a similar wavelength sion if the aperture does not cover the full extent of the out-
range (Feiiλ2344, λλ2374,2382, and λλ2586,2600), the Mgii flowing envelope (Scarlata & Panagia 2015), integral field ob-
doublet is particularly sensitive to emission infilling, since its servationseliminateapertureeffectsfordistantgalaxies,making
lower energy level does not have fine structure splitting. As a emission signatures easier to detect. The combined spatial and
result of the different possible relative strengths of the emis- spectroscopicdatafacilitatecharacterizingthemorphologyand
sion and absorption components, observed profiles for the res- kinematics of both star-forming galaxies and the outflows they
onant Mgiiλλ2796,2803 transitions vary greatly for different produce.
star-forminggalaxies(Weineretal.2009;Rubinetal.2011;Coil Inthispaper,weanalyzegalacticwindsignaturesfromaspa-
etal.2011;Erbetal.2012;Martinetal.2012,2013;Korneietal. tiallyresolvedstar-forminggalaxyatz = 1.2902observedwith
2013). MUSE.WepresenttheobservationsinSection2andsummarize
Thethirdpossiblesignatureofoutflowsinemissionisfrom thegalaxypropertiesinSection3.Withtheintegrated1DMUSE
non-resonanttransitionssuchasCii*,Siii*(e.g.,Shapleyetal. galaxyspectrum,wecharacterizeoutflowsignaturesfromFeii,
2003)orFeii*(e.g.,Rubinetal.2011).Detectingnon-resonant Mgii,andMgitransitionsinabsorptionandFeii*transitionsin
Articlenumber,page2of13
HayleyFinleyetal.:GalacticWindswithMUSE:ADirectDetectionofFeii*Emissionfromaz=1.29Galaxy
emissioninSection4.Wetheninvestigatethespatialextentand Table1.GalaxyID#13propertiesfromContinietal.(2016)
thekinematicpropertiesoftheFeii*emissioninSections5and
6,respectively.InSection7,wecompareourobservationswith MorphologicalAnalysis HST+Galfit
radiative transfer wind models and estimate the mass outflow Positionangle(◦) −45.9±1.9
rate.WereviewourfindingsinSection8.Throughoutthepaper, Inclinationi(◦) 33±5
weassumeaΛCDMcosmologywithΩm = 0.3,ΩΛ = 0.7,and Half-lightradius(kpc) 2.1±0.03
H0 = 70 km s−1 Mpc−1. With this cosmology, 1 arcsec corre- KinematicAnalysis MUSE2D/3D
spondsto8.37kpcattheredshiftofthegalaxy. Positionangle(◦) −14/−13
Inclinationi(◦) +28/+17
Max.rotationalvelocity(kms−1) +24/+44
2. Data Velocitydispersion(kms−1) +48/+46
MUSE fully covers the wavelength range 4650−9300 Å with PhotometricAnalysis SEDfitting
1.25 Å per spectral pixel. The field of view spans 1(cid:48) ×1(cid:48) with VisualextinctionAV(mag) 1.20+−00..5296
a pixel size of 0.2(cid:48)(cid:48). The instrument is notable both for its high log(M(cid:63))(M(cid:12)) 9.89±0.11
throughput,whichreaches35%at7000Å(end-to-endincluding log(SFR)(M(cid:12)yr−1) 1.89±0.18
the telescope), and its excellent image quality sampled at 0.2(cid:48)(cid:48)
perspaxel.WhileMUSEopensnewavenuestoaddressawide
varietyofscientificquestions,thesetwocharacteristicsmakethe morphologyfromHSTimagesintheF814Wbandbymodelling
instrumentoptimalfordeepfieldobservations. thegalaxywithGalfit(Pengetal.2002)asabulgeplusanex-
As part of commissioning data taken during July and Au- ponential disk. Contini et al. (2016) then performed the kine-
gust 2014, MUSE observed a 1(cid:48) ×1(cid:48) field of view in the Hub- matic analysis with two different techniques: a traditional 2D
ble Deep Field South (HDFS) for a total integration time of 27 line-fittingmethodwiththeCamelalgorithm(Epinatetal.2012;
hours.Thefinaldatacubeisa5σ-clippedmeanof54individual Contini et al. 2016) combined with a 2D rotating disk model,
exposuresthatweretakenindarktimeundergoodseeingcondi- whichrequirespriorknowledgeofthegalaxyinclination,anda
tions(0.5(cid:48)(cid:48)−0.9(cid:48)(cid:48)).The1σemission-linesurfacebrightnesslimit 3Dfittingalgorithm,GalPaK3D (Bouchéetal.2015),whichsi-
forthiscubeis1×10−19ergs−1 cm−2 arcsec−2.TheMUSEob- multaneously fits the morphological and kinematic parameters
servationsprovidedspectroscopicredshiftsfor189sourceswith directlyfromtheMUSEdatacube.Theparametersfromthe2D
magnitude I ≤ 29.5 (8 stars and 181 galaxies), a factor-of- and3Dmodelsareingoodagreementoverall(seeTable1).
814
tenincreaseoverthe18previously-measuredspectroscopicred- FromthemorphologicalanalysisontheHSTimages,galaxy
shifts in this field. A catalogue of sources in the MUSE HDFS ID#13 is compact with a disk scale length of Rd = 1.25 kpc
fieldincludestheredshifts,emission-linefluxes,and1Dspectra. (correspondingly R1/2 = 2.1 kpc) and has a low inclination an-
The observations, the data cube, and an overview of scientific gle of i = 33◦. The inclination from 3D fitting yields a lower
exploitationsarefullydescribedinBaconetal.(2015).Boththe value of ∼ 20◦. The disagreement likely arises from an asym-
datacubeandthecatalogueofsourcesarepubliclyavailable.1 metric morphology seen in the HST images, since statistically
ThedeepIFUobservationsrevealemissionfromFeii*tran- thetwotechniquesmeasureinclinationsthatareingoodagree-
ment (Contini et al. 2016). The galaxy also shows a misalign-
sitions directly detected from one galaxy in the MUSE HDFS.
mentbetweenthemorphologicalpositionanglemeasuredfrom
ThegalaxyhasID#13intheMUSEcatalogue,withcoordinates
α = 22h32m52.16s, δ = −60◦33(cid:48)23.92(cid:48)(cid:48) (J2000) and magni- theHSTimage,−46◦,andtheMUSEkinematicpositionangle,
tude I = 22.83 ± 0.005. It is part of a 9-member group at −13◦, again likely due to the asymmetric light distribution that
814
z (cid:39) 1.284, discussed in Bacon et al. (2015), that also includes onlyappearsathigherspatialresolution.Regardless,thegalaxy
hasalowinclinationwithi∼20◦−30◦.
two AGN and an interacting system with tidal tails. This direct
detectionofagalaxywithFeii*emissionoffersanewopportu- FromthekinematicanalysisontheMUSEdata,thevelocity
fieldhasalowgradient,±10kms−1,alowmaximumvelocity,
nitytocharacterizegalacticwinds.
24kms−1,andavelocitydispersionof45−50kms−1.There-
fore,non-circularmotionsdominatethegasdynamicswithinthe
3. GalaxyProperties disk, with V/σ ≈ 0.5, i.e. below the commonly-used V/σ ≤ 1
threshold for identifying dispersion-dominated galaxies. Note
GalaxyID#13ispartofasampleof28spatiallyresolvedgalax- thatthedifferentmaximumvelocitiesfromthe2Dand3Dmeth-
ies that Contini et al. (2016) selected from the MUSE HDFS odsareentirelyduetothedifferentinclinationvalues(Table1).
accordingtothecriterionthatthebrightestemissionlinecovers Nonetheless,theratioremainsV/σ(cid:46)1fortherangeofpossible
atleast20spatialpixelswithasignal-to-noiseratio(S/N)higher inclinations,17◦−33◦.
than 15. For this galaxy, emission from the [Oii]λλ3727,3729 Contini et al. (2016) estimated the visual extinction, A =
V
doublet is the dominant feature in the MUSE spectrum. We 1.20mag,stellarmass,M =8×109M ,andstarformationrate
(cid:63) (cid:12)
determined the galaxy systemic redshift from a p-v diagram SFR = 77+40 M yr−1,fromStellarPopulationSynthesisusing
−25 (cid:12)
extracted from the MUSE data cube along the galaxy kine- broad-bandvisibleandnearinfra-redphotometry2.Thegalaxy
matic major axis by fitting a double Gaussian profile to the
ID#13 is one of the most massive of the 28 spatially-resolved
[Oii]λλ3727,3729emissionateachpositionalongtheslit.The
galaxiesintheMUSEHDFSsampleandalsohasthehigheststar
systemic redshift of z = 1.29018±0.00006 is the mean value
formationrate(SFR).ThisSFRplacesgalaxyID#13abovethe
betweenthetwoasymptotesoftherotationcurve.
main sequence (Elbaz et al. 2007; Karim et al. 2011; Whitaker
Contini et al. (2016) investigated the morphological and
etal.2014;Tomczaketal.2016)byalmost1dex,indicatingthat
kinematicpropertiesofthegalaxyID#13,aspartoftheMUSE
HDFS spatially resolved galaxy sample. They constrained the 2 The[OII]-derivedSFRforaChabrier(2003)IMFis65M yr−1us-
(cid:12)
ingtheKewleyetal.(2004)calibration,whichalsoyieldsanextinction
1 http://muse-vlt.eu/science/hdfs-v1-0/ ofA =1.5inthegas.
V
Articlenumber,page3of13
A&Aproofs:manuscriptno.FeII
t
1)− 5 uble plet 2365 2396 2612 2626 2632
y˚2A− 4 I]do I]tri II*λ II*λ II*λ II*λ II*λ
sitm CI CI Fe Fe Fe Fe Fe
nc 3
De1−
xs 6 3
ug 2 4 4 2 6 0 9 0 2
Fler 34 37 38 58 60 27 28 85
8 2 2 2 2 2 λ λ 2
1− 1 Iλ Iλ Iλ Iλ Iλ II II Iλ
0 I I I I I g g g
1 Fe Fe Fe Fe Fe M M M
(
0
2300 2400 2500 2600 2700 2800
Rest Wavelength (˚A)
Fig.1.Vacuumrest-frame1DspectrumoftheMUSEHDFSgalaxyID#13coveringtheFeiiandMgiitransitions.Thespectrumisinblackwith
the1σerrorinmagenta.Resonanttransitionsdetectedinabsorptionarelabeledinblue.Non-resonantFeii*transitionsdetectedinemissionare
labeledinred.TheCii]nebularemission,whichisablendoffivetransitions,islabeledingreen.
this galaxy is undergoing a starburst with a high specific SFR We fit these profiles simultaneously with VPFIT4 v10, using
of sSFR = 10 Gyr−1. The starburst phase of galaxy evolution several components and requiring each to have the same red-
canproducelarge-scaleoutflowswhenmanyshort-livedmassive shiftandDopplerparameteracrossthedifferenttransitions.The
starsexplodeassupernovae. absorptions are well-fitted with three components at redshifts
Thepropertiesofthisgalaxyareconducivetodetectingsig- 1.28514±0.00021,1.28752±0.00009,and1.29024±0.00006,
natures from galactic winds. The low inclination angle favors correspondingtoshiftsof−660±28kms−1,−349±12kms−1
observing blue-shifted absorptions, given that this signature in- and +8.5±6.5 km s−1 relative to the galaxy systemic velocity.
creasessubstantiallytowardsface-ongalaxies(Chenetal.2010; Table 2 summarizes the total rest-frame equivalent widths for
Kornei et al. 2012; Rubin et al. 2014). The [Oii] luminosity eachtransition,calculatedbothfromthefitanddirectlyfromthe
(∼ 1043 erg s−1) and rest-frame equivalent width (∼ 50 Å, see flux.
Table 3) indicate that the galaxy ID#13 is also well-suited for Globally,theFeiiresonanttransitionsinFigure2revealsev-
investigatingwindsinemission,sinceFeii*andMgiiemission eral key features: (1) the Feii profiles are very similar to one
correlatewith LOii or[Oii]rest-frameequivalentwidth(Kornei another, and (2) the strongest component is roughly centered
etal.2013;Zhuetal.2015). at the galaxy systemic redshift. As Prochaska et al. (2011) first
demonstrated,emissioninfillinginresonantabsorptionlinescan
alter doublet ratios and mimic partial coverage. However, here
4. Absorptionandemissionprofilesfromthe1D wefindthatemissioninfillingdoesnotplayasignificantrolein
thisgalaxyforthefollowingtwoqualitativearguments.
spectrum
First,whilestrongemissioninfillingwouldproduceclearP-
In this section, we analyze the galaxy ID#13 1D spectrum cygni profiles (which are not observed), moderate amounts of
extracted from the MUSE data using a white-light weighting emission infilling would cause a blue-shift to the centroid of
scheme. The 1D MUSE spectrum (Figure 1) reveals resonant theabsorption,aneffectcommonlyseeninstackedspectra(e.g.,
Feii, Mgii, and Mgi self-absorption, non-resonant Feii* emis- Zhu et al. 2015) or individual cases (Rubin et al. 2011; Martin
sion,andCii]and[Oii]nebularemissionlines.TheFeiitransi- etal.2013).NoneoftheabsorptionsinthegalaxyID#13spec-
tionsoccurinthreemultiplets3.IntheFeiiUV1,UV2,andUV3 trum(Figure2)haveblue-shiftedcentroids.
multiplets,aphotoncanbere-emittedeitherthrougharesonant Second, because Feii has multiple channels to re-emit the
transition to the ground state, which produces emission infill- photons(throughresonantandnon-resonanttransitions),thede-
ing, or through a non-resonant transition to an excited state in gree of infilling for a particular Feii absorption line depends
the lower level, in which case the emission occurs at a slightly on the likelihood of re-emission through the different channels
different wavelength. We investigate the integrated absorption withinamultiplet.Purelyresonanttransitions,suchasMgiiand
and emission profiles, focusing first on the resonant absorption Feiiλ2383,arethemostsensitivetoemissioninfilling.Zhuetal.
andemissionproperties(Section4.1),thenonthenon-resonant (2015) demonstrated that the Feii resonant absorptions that are
emissionproperties(Section4.2). the least (most) affected by emission infilling are Feiiλ2374
(Feiiλ2600 and Feiiλ2383) respectively. Figure 2 shows that
theFeiiλ2374,λ2600andλ2383absorptionprofilesareallvery
4.1. ResonantFeandMgprofiles
similarforthegalaxyID#13.Thelackofblue-shiftedcentroids
Figure 2 compares the velocity profiles of each of the individ- andtheconsistentabsorptionprofilesarguestronglyagainstthe
ual Feii, Mgii, and Mgi transitions relative to the galaxy sys- presenceofdetectableemissioninfillinginthisgalaxy.
temicredshift.Theself-absorptionprofilesareasymmetric,with We quantify (and put a limit on) the global amount of in-
the strongest component centered on the galaxy systemic red- filling using the method proposed by Zhu et al. (2015), which
shift, and a significant blue wing extending to −800 km s−1. consistsofcomparingtheobservedrest-frameequivalentwidths
3 SeeTangetal.(2014)orZhuetal.(2015)forenergyleveldiagrams. 4 http://www.ast.cam.ac.uk/~rfc/vpfit.html
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HayleyFinleyetal.:GalacticWindswithMUSE:ADirectDetectionofFeii*Emissionfromaz=1.29Galaxy
1.25 1.50
1.00 1.25
0.75 1.00
0.75
0.50
0.50
0.25 Feii λ2344 0.25 Feii* λ2365
1.25
1.50
2000 1000 0 1000 2000
1.00 1.25 − −
0.75 1.00 Velocity (km s 1)
−
0.50 0.75
0.25 Feii λ2374 0.50
x 0.25 Feii* λ2396
1.25 u
1.00 Fl 1.50 2000 1000 0 1000 2000
1.25 − −
00..5705 zed 01..7050 Velocity (km s−1)
i
ux 0.25 Feii λ2382 mal 00..2550 Feii* λ2612
dFl 11..0205 Nor 1.50 2000 1000 0 1000 2000
e 0.75 1.25 − −
aliz 0.50 01..7050 Velocity (km s−1)
m 0.25 Feii λ2586 0.50
r
No 1.25 0.25 Feii* λ2626
1.00
2000 1000 0 1000 2000
0.75 15 − [Oii] λ−3729
0.50 Velocity (km s 1)
−
0.25 Feii λ2600
1.25 10
1.00 Velocity (km s−1)
0.75
0.50 5
0.25 Mgii λ2796
1.25
Mgii λ2803
1.00 0
0.75 2000 1000 0 1000 2000
− −
0.50 Velocity (km s 1)
0.25 −
1.25 Fig.3.Feii*and[Oii]emissionpeaksdetectedinthenormalized1D
1.00 MUSEspectrum.ThegreencurvetracesjointGaussianfitstothefour
0.75 Feii* emission peaks and the [Oii] doublet, respectively. Zero veloc-
0.50 ity,indicatedwiththeverticalreddashedline,isrelativetothegalaxy
0.25 Mgi λ2853 systemicredshift,z=1.2902,measuredfromthe[Oii]emission.
1500 1000 500 0 500 1000 1500
− − −
Velocity (km s 1)
− Weareunabletoputconstraintsontheweakcomponent‘A’,but
Fig.2.Feii,Mgii,andMgitransitionsdetectedinabsorptioninthe1D the blue-shifted component ‘B’ at −350 km s−1 does not allow
MUSEspectrum.Errorbarsshowthe1-σerrorontheflux(black),and foremissioninfillingthatwouldincreasetheFeiiλ2383equiva-
thegreencurvetracesthefittotheabsorptionprofiles.Zerovelocityis lentwidthbymorethan10%.Thecomponent‘C’atthegalaxy
relativetothegalaxysystemicredshift,z=1.2902.Verticalbluedashed systemic redshift allows for the largest amount of emission in-
linesmarkthethreecomponentsusedtofiteachabsorption,andgray fillingwith60%correctionsforFeiiλ2600andFeiiλ2383,40%
dashedlinesshowcomponentsthatarepartofneighboringtransitions. for Feiiλ2344 and 20% for Feiiλ2586. As we discuss later in
Theasymmetricabsorptionprofilesindicatesignificantblue-shiftedab- Section7.2,theblue-shiftedgalacticwindcomponent(‘B’)ap-
sorption. pearstobelessaffectedbyemissioninfillingthanthesystemic
componentassociatedwiththegalaxyISM(‘C’).
Weendthissectionbymentioningthat,aswewillarguein
of the resonant lines to those seen in intervening quasar spec-
section 7.2, the Feii and Mgii gas is likely optically thick. The
tra(seetheirFigure12).Usingtheaveragedrest-frameequiva-
lentwidthsofresonantFeiiandMgiiabsorptionsfromastacked absorptionsoughttobesaturated,andthereasonwedonotob-
spectrumof∼30strongMgiiabsorbergalaxiesat0.5<z<1.5 serve fully absorbed profiles is either due to a partial covering
fraction(ratherthanemissioninfilling)ormorelikelytothelow
from Dutta et al. (2017, their Table 7), we find that our data is
spectralresolution.Aswewillshowinthenextsection,thenon-
consistent with no emission infilling. Our data could allow for
atmost<0.8Å(<1.8Å)ofinfillingforFeiiλ2600(Feiiλ2383), resonantFeii*emissionpatternisalsoconsistentwithoptically
thickgas.
thetwotransitionsmostsusceptibletoinfilling(Zhuetal.2015).
This means that at most 22% (55%) of these absorptions could
beaffectedbyinfillingandthattheimpactontheotherFeiiab-
4.2. Non-resonantemission
sorptionsisevensmaller.
Similarly,weseparatelyestimatetheamountofinfillingfor Figure3showsthenon-resonanttransitionsFeii*λ2365,λ2396,
each of the three sub-components shown in Figure 2 (Table 2). λ2612, and λ2626 that we detect in the MUSE HDFS galaxy
Articlenumber,page5of13
A&Aproofs:manuscriptno.FeII
ID#131Dspectrumat2.5σ−6σsignificance.NoFeii*λ2632 toobtainthe[Oii]surfacebrightnessmapshowninthebottom
emission is detected (Figure 1). The fluxes in the non-resonant leftpanelofFigure4.
transitions Feii*λ2365, λ2396, λ2612, λ2626 transitions are TheFeii*mapinFigure4isthefirsttwo-dimensionalspatial
1.2 − 2.4 − 1.5 − 2.7 × 10−18 egs s−1 cm−2, respectively. Ta- map of the Feii* non-resonant emission in a individual galaxy
ble 3 gives the emission peak fluxes and rest-frame equivalent atintermediateredshift.Previousstudieshavelookedforsigna-
widths measured for all of the Feii* transitions. These flux ra- tures of extended Feii* emission in stacked spectra (Erb et al.
tios of 0.5 : 1.0 : 0.6 : 1.0 are consistent with the expectation 2012; Tang et al. 2014). In a stacked spectrum from 95 star-
(0.66:1.0:0.66:1.0)foropticallythickgasdiscussedinTang forming galaxies at 1 < z < 2, Erb et al. (2012) found that
etal.(2014).Intheopticallythinregime,thefluxratiosshould theFeii*λ2626emissionlineisslightlymorespatiallyextended
beontheorderof∼1. thatthestellarcontinuum.Tangetal.(2014)performedasimilar
Regarding the non-detection of Feii*λ2632, we note that analysiswith97star-forminggalaxiesat1 (cid:46) z (cid:46) 2.6,butwere
this transition is usually not detected in stacked spectra (Talia notabletospatiallyresolvetheFeii*emission.
etal.2012;Korneietal.2013;Tangetal.2014;Zhuetal.2015), Thanks to the sensitivity of MUSE, we are able to address
exceptforintheErbetal.(2012)stackedspectrum,butthatitis whetherFeii*ismoreextendedthanthecontinuumandtochar-
observed in the other individual cases (Rubin et al. 2011; Mar- acterize the Feii* emission morphology for the first time. The
tin et al. 2013). Tang et al. (2014) explore whether underlying top left panel of Figure 4) shows that the extended Feii* emis-
stellar absorption suppresses the Feii*λ2632 emission in their sion(solidcontour)appearstobemoreextendedthanthecontin-
stackedspectra.However,forthisstarburstgalaxy,theF-andG- uum(dashedcontour)andhasaprivilegeddirection.Comparing
typestarsthatproducetheunderlyingabsorptionareunlikelyto theFeii*emissionpositionanglewiththekinematicaxisofthe
significantlycontributetothestellarcontinuum. galaxy,indicatedwithcrosses,showsthattheFeii*ismoreex-
We perform a joint Gaussian fit to the four non-resonant tendedalongtheminorkinematicaxisofthegalaxy.
Feii* emission peaks and find that they appear symmetric To quantify the extent of the Feii*, stellar continuum, and
and centered on the galaxy systemic redshift measured from [Oii]λλ3727,3729 emission, we use a custom Python MCMC
[Oii]λλ3727,3729 (Figure 3). This is in contrast to Zhu et al. algorithm to fit each of the surface brightness maps in the left
(2015), who found that the Feii* emission from their stacked columnofFigure4withaSersicprofile.Thefitprovidesuswith
spectrum of 8,600 galaxies is slightly asymmetric, and in con- intrinsicparametersandwithanintrinsicmodeloftheemitting
trasttoRubinetal.(2011),whoobservedFeii*emissionpeaks region, i.e. deconvolved from the seeing, because we convolve
thatareslightly(∼ 30kms−1)redshiftedrelativetothenebular the Sersic profile with the actual PSF taken from the brightest
emissionlines. starinthesamedatacube,MUSEHDFSID#1(seeBaconetal.
2015),acrosswavelengthscorrespondingtothegalaxyemission
lines5.Inpractice,wefixtheSersicindexnton=1orn=0.5
5. MorphologyoftheFeii*Emission becausetheSersicindexnisunconstrained6.Thesizeestimate,
R , is nonetheless robust and independent of the Sersic index
Inthissection,weinvestigatewhethertheFeii*emissionhasa 1/2
n,sinceitisdeterminedempiricallyfromthefluxgrowthcurve,
similar spatial extent and morphology as the stellar continuum
anintegratedquantity.
andthe[Oii]λλ3727,3729emission.
Table 4 summarizes the results from this analysis and Fig-
For the Feii* emission, first we produce a sub-cube of size ure 4 (middle column) shows the modeled profiles for n = 1
1.5(cid:48)(cid:48)×1.5(cid:48)(cid:48)foreachofthefouremissionlinesandtransformthe for the Feii*, stellar continuum, and [Oii] emission. The right
wavelengthaxistovelocityspace.Weinterpolateeachsub-cube column of Figure 4 gives the residual maps, which are the dif-
to the same velocity scale with pixels of 30 km s−1 that span ferencebetweentheobserveddataandtheintrinsicmodelcon-
±930 km s−1 and zero velocity at the galaxy systemic redshift, volvedwiththeseeing.
z=1.2902. The stellar continuum emission (Figure 4, middle row) ap-
Wesubtractthecontinuumandcombinethefoursub-cubes. pearsroundandcompact.Theintrinsicemissionfromtheexpo-
To estimate the stellar continuum, we use the mean value from nential disk fit yields an inclination of 28±3◦ and a half-light
two regions redwards of the Feii* emission peaks at ∼ λ2425 radius, R , of around 0.28 ± 0.02(cid:48)(cid:48) (2.34 ± 0.17 kpc). These
1/2
and ∼ λ2700 Å that span 115 Å and 300 Å respectively. The continuum emission properties from MUSE are comparable to
continuumpseudonarrowbandimageshowninFigure4(middle themeasurementsfromHSTimagesdiscussedinSection3and
left) is from the mean of these two continuum regions, which shown in Table 1. The [Oii]λλ3727,3729 emitting region has
haveaflatslope. thesamemorphologybutisslightlymoreextendedthanthestel-
From the combined Feii* emission velocity cube, we then larcontinuumwithR1/2,[Oii] =0.33±0.02(cid:48)(cid:48) (2.76±0.17kpc).
extract a narrow band (NB) image by summing 13 pixels ThecorrespondingstarformationratesurfacedensityisΣ =
SFR
(±390kms−1).ThetopleftpanelofFigure4showsthepseudo- 1.6M kpc−2.
(cid:12)
narrowbandFeii*imagewith2×2smoothing,andweusethis The Feii* emission has a morphology and physical extent
image for the analysis. For comparison, we also tested an au- that are different from the stellar continuum and [Oii] emis-
tomated extraction with the CubExtractor software (Cantalupo sion.TheintrinsicFeii*emissionismoreellipticalwithanaxis
etal. inprep.),whichselectsconnectedvolumepixels(voxels) ratio of b/a = 0.57, compared to the rounder continuum and
that are above a specified SNR threshold (2.7 was optimal in
ourcase)toproduceoptimallyextractedimages,asinBorisova 5 The PSF can be approximately described by a Moffat profile with
et al. (2016). Our morphological results are independent of the FWHM 0.70(cid:48)(cid:48) (0.63(cid:48)(cid:48)) at the Feii* and stellar continuum emission
methodusedtoproducetheFeii*NBimage. ([Oii]emission)wavelengths,whichcorrespondstoahalf-lightradius
Similarly, we create the [Oii] pseudo-narrow band image of0.50(cid:48)(cid:48)(0.44(cid:48)(cid:48)).
6 The Sersic n index is unconstrained because the seeing radius
froma30×30pixel(1.5(cid:48)(cid:48)×1.5(cid:48)(cid:48))sub-cubethatspans18spec-
is much larger than the emission. Indeed, the seeing radius is
tral pixels (22.5 Å) to cover the λλ3727,3729 doublet. Again, FWHM/2=0.35(cid:48)(cid:48), corresponding to R ≈0.5(cid:48)(cid:48) for a Moffat profile,
1/2
wesubtractthecontinuumestimatedbetween∼ 3550−3600Å whereasthegalaxy’sintrinsichalf-lightradiusR isonly≈0.3(cid:48)(cid:48).
1/2
Articlenumber,page6of13
HayleyFinleyetal.:GalacticWindswithMUSE:ADirectDetectionofFeii*Emissionfromaz=1.29Galaxy
RA Offset (proper kpc)
-20.1-13.4-6.7 0.0 6.7 13.420.1 -20.1-13.4-6.7 0.0 6.7 13.420.1 -20.1-13.4-6.7 0.0 6.7 13.420.1
2.4 20.1
MUSE Feii Model Feii Data (Model Seeing)
∗ ∗
− ∗
1.6 13.4
0.8 6.7
0.0 0.0
-0.8 -6.7
-1.6 -13.4
-2.4 -20.1
)
ec 0 2 4 6 -2.0-1.5-1.0-0.5 0 0.5 1.0 1.5 2.0
s
c
r
a
(
2.4 20.1
400 MUSE Stellar Continuum Model Stellar Continuum
3.9 1.6 13.4 pc)
2 k
330 0.8 6.7 per
◦ o
0 r
6 0.0 0.0 p
- (
o t
t e
tive -0.8 -6.7 Offs
rela -1.6 -13.4 Dec
et -2.4 -20.1
s
ff
O
c
e
D
0 2 4 6 8 10 12 -0.5 -0.25 0 0.25 0.5
2.4 20.1
MUSE [Oii] Model [Oii]
1.6 13.4
0.8 6.7
0.0 0.0
-0.8 -6.7
-1.6 -13.4
-2.4 -20.1
-2.4 -1.6 -0.8 0.0 0.8 1.6 2.4 -2.4 -1.6 -0.8 0.0 0.8 1.6 2.4 -2.4 -1.6 -0.8 0.0 0.8 1.6 2.4
RA Offset relative to 338 13 02.26 (arcsec)
◦ 0 00
0 15 30 45 60 75 90 105 5 4 3 2 1 0 1 2 3 4 5
− − − − −
Surface Brightness (10 18 erg s 1 cm 2 arcsec 2)
− − − −
Fig.4.Leftpanels:Surfacebrightnessmapsof Feii*(top),stellarcontinuum(middle),and[Oii]emission(bottom)frompseudonarrowband
images (see text). Solid contours represent 1/10 of the maximum surface brightness. The dashed line in the top left panel correspond to the
stellarcontinuumcontourfrommiddleleftpanel.Thesmallblackcirclesrepresenttheseeingattheemissionwavelength.Middlepanels:Surface
brightnessmapsoftheintrinsicemissionfromanexponentialdiskmodel‘deconvolved’fromtheseeing.Ellipsesinthemiddlecolumnaredrawn
usingthemodelparametersandhaveasizethatcorrespondstothehalf-lightradii(seeTable4).Rightpanels:Mapsoftheresidualsbetweenthe
observeddataandtheintrinsicmodelconvolvedwiththeseeing.ThewhitecrossesindicatethegalaxymajorandminoraxesfromtheContini
etal.(2016)kinematicanalysis.TheFeii*emissionmapismoreextendedthanboththestellarcontinuumorthe[Oii]emission.
Articlenumber,page7of13
A&Aproofs:manuscriptno.FeII
2 PA=-20 2 Cont.
FeII*
1 1
) )
" "
( 0 ( 0
y p
∆ ∆
1 1
2 2
2 1 0 1 2 1 800 400 0 400 800 0 1
∆x (")
0
800 400 0 400 800
2 PA=70 2
1 1
) )
" "
( 0 ( 0
y p
∆ ∆
1 1
2 2
2 1 0 1 2 1 800 400 0 400 800 0 1
∆x (") V (km/s)
sys
0
800 400 0 400 800
V (km/s)
sys
Fig.5.Leftpanels:NarrowbandimagesoftheFeii*emissionoptimallyextractedfromtheMUSEcubeshownwitha1(cid:48)(cid:48)-wideslitoriented-20◦
(top)and+70◦ (bottom).The+70◦ slitorientationinthebottompanelsfollowstheFeii*majorkinematicaxis.Thewhitecrossesindicatethe
galaxymajorandminoraxesfromtheContinietal.(2016)kinematicanalysisof[Oii].Rightpanels:Position-velocitydiagramsoftheFeii*
emission from a slit oriented -20◦ (top) and +70◦ (bottom). Zero velocity is relative to the galaxy systemic redshift, z =1.29018±0.00006,
measuredfromthe[Oii]emission.SolidblackcontourstraceFeii*fluxlevelsat2,6,10,14,and18×10−20ergs−1cm−2.Dashedblackcontours
showthenegativefluxlevelsat-2and-4×10−20 ergs−1 cm−2.Theredgradientindicatesthecontinuumintensity.Therightsidepanelofeach
p-v diagram compares the spatial profile of the Feii* emission (black) with that of the stellar continuum (red). The bottom sub-panel of each
p-vdiagramshowsthetotal1Dfluxspectrumintegratedacrossthespatialregionbetweenthesolidgreenhorizontallinesinthep-vdiagram.In
thebottomp-vdiagram,thewhitesolidlinefollowsthevelocitygradients.Thispanelalsorevealsa‘C’-shapepatterninthebluewingofthe
Feii*emissionextendingto-400kms−1.ThebluewingoftheFeii*emissionismorepronouncedalongtheslitorientationcorrespondingtothe
minor-axis(PA=+70◦).
[Oii] emission, which both have b/a (cid:39) 0.9. The Feii* emis- this70degslitorientation(bottomrow)andforaslitorientedat
sion is elongated along the direction (PA ≈ +60◦) that roughly −20deg(toprow).Inbothcases,theslitwidthis1(cid:48)(cid:48).Following
corresponds to the galaxy minor kinematic axis (PA ≈ +75◦, the peak of the Feii* emission, we see that the Feii* emission
Table 1). Moreover, the intrinsic half-light radius of the Feii* has a velocity gradient along the galaxy minor kinematic axis.
emissionisR1/2,Feii∗ =0.49±0.05(cid:48)(cid:48),i.e.about50%largerthan Thewhitesolidlineinthebottom p−vdiagramguidestheeye
thatofthestellarcontinuum.Inotherwords,theFeii*half-light alongthisvelocitygradient.BlackcontourstracetheFeii*emis-
radius, R1/2,Feii∗ = 4.1 ± 0.4 kpc, extends (cid:38) 1.5 kpc beyond sion,andtheredshadedareaindicatesthecontinuum.
the stellar continuum and the [Oii] emission, which both have Figure5revealstwoadditionalresults.First,theFeii*emis-
R ≈ 2.5 kpc (Table 4). This is apparent from comparing the sion shows an extended blue-wing, which is more pronounced
1/2
extent of the Feii* emission (solid contour) to the continuum in the PA = +70 profile. Secondly, the blue-side of the Feii*
emission(dashedcontour)inthetopleftpanelofFigure4.See emission contours in the bottom panel, with the slit oriented
Table4fortheemissionproperties. at +70 deg, shows a C-shaped pattern. The contours extend to
−400kms−1 near+1(cid:48)(cid:48) and−1.5(cid:48)(cid:48),butdecreaseto−200kms−1
in between. This C-shape pattern is characteristic of a hollow
6. KinematicsoftheFeii*emission
conicalemission,ascouldbeexpectedfromanoutflow.
Inthissection,weinvestigatewhetheritispossibletotracethe
kinematicsoftheFeii*emission.Todoso,wevisuallyinspected
7. Discussion
thevelocitycubeproducedintheprevioussectionandfoundthat
thekinematic majoraxis fromtheFeii*emission followsa PA From deep MUSE observations of the HDFS, we identify a
of about 70 deg, which happens to correspond roughly to the spatially-resolved galaxy (ID#13) at z = 1.2902 that has a low
galaxyminorkinematicaxis.Figure5shows p−vdiagramsfor inclination (i = 33◦), an orientation that may favor detecting
Articlenumber,page8of13
HayleyFinleyetal.:GalacticWindswithMUSE:ADirectDetectionofFeii*Emissionfromaz=1.29Galaxy
0.1
˚A) 0.0 UV1 ˚A) 0.5 UV1 ˚A) 0.0 UV1
( ( (
0 0 0 0.1
W 0.5 W 0.0 W −
− 0.2
6 2 2 −
262 −1.0 261 −0.5 263 −0.3
λ λ λ 0.4
−
i* 1.5 i* 1.0 i* 0.5
ei − ei − ei −
F F F 0.6
2.0 1.5 −
− 1 2 3 4 5 − 0 1 2 3 4 0 1 2 3 4
Feii λ2600 W (˚A) Feii λ2586 W (˚A) Feii λ2586 W (˚A)
0 0 0
0.0 0.0
This Work
˚(A) −0.2 UV2 ˚(A) 0.2 UV3 Rubin et al.(2011)
0 0 −
W 0.4 W Martin et al.(2013)
− 0.4
96 0.6 65 − Prochaska et al.(2011) models:
23 − 23 0.6 Fiducial
λ 0.8 λ −
* − * θb =80◦ θb =45◦
Feii −1.0 Feii −0.8 τdust =1 τdust =3
1.2 1.0 ISM ISM + dust
− 0.5 1.0 1.5 2.0 2.5 − 1.0 1.5 2.0 2.5 3.0 3.5 4.0
Feii λ2374 W (˚A) Feii λ2344 W (˚A)
0 0
Fig.6.Observedandmodeledrest-frameequivalentwidthsfromtheFeiiUV1,UV2,andUV3multiplettransitions.Star-shapedpointsindicate
valuesmeasuredfromthethreedirectdetections:thiswork(blue),Rubinetal.(2011)(yellow),andMartinetal.(2013)(red).Circularpointsinthe
toppanelscomefromradiativetransfermodelpredictionsfortheUV1multiplet(Prochaskaetal.2011).Colorsrepresentvariationstothefiducial
isotropicoutflowmodel(black)thattestdifferentopeningangles(θ )forbi-conicaloutflows,dustopacities,andincludeanISMcomponent.See
b
Prochaskaetal.(2011)foradditionalmodelvariations.ModelpredictionsfortheFeiiUV2andUV3multipletsarenotcurrentlyavailable.
galactic outflows in emission (Rubin et al. 2014). This galaxy more extended along one axis suggests that the outflow is not
hasastarformationrateofSFR = 77+40 M yr−1,whichplaces isotropic.Isotropicoutflowsare,however,thefiducialgeometry
−25 (cid:12)
itinthestarburstcategory(SeeContinietal.2016,theirFigure forradiativetransferandsemi-analyticwindmodels(Prochaska
3).ItsstarformationratesurfacedensityisΣ =1.6M kpc−2, et al. 2011; Scarlata & Panagia 2015). Comparing these mod-
SFR (cid:12)
wellabovethethresholdforgalacticwinds(Newmanetal.2012; elsandtheirvariationswithdirectdetections,suchastheMUSE
Bordoloi et al. 2014). The star formation rate and stellar mass HDFSgalaxyID#13,canhelptointerprettheobservationswhile
arenearlyidenticaltothoseoftwogalaxiesatz=0.694(Rubin motivatingadditionalrefinementstothemodels.
etal.2011)andz = 0.9392(Martinetal.2012)thatbothshow
direct evidence of galactic winds from blueshifted absorptions, The radiative transfer and semi-analytic models of galactic
redshiftedMgiiemission,andnon-resonantFeii*emission. outflows from Prochaska et al. (2011) and Scarlata & Panagia
(2015)bothpredictconcurrentresonantandnon-resonantemis-
In the integrated 1D MUSE spectrum, we detect non-
resonantFeii*emissionbutnoapparentresonantFeiiandMgii sion,becauseabsorbedphotonscanbere-emittedviaeithernon-
emission,differentiatingthisgalaxysomewhatfromthetwopre- resonantorresonanttransitionsformultiplets(Tangetal.2014;
Zhuetal.2015).ThespectrumoftheHDFSgalaxyID#13(Fig-
viousexamples.Wealsoobtainthefirstdirectdetectionofspa-
tially extended Feii* emission (Section 5) from an individual ures1and2)showsstrongFeiiandMgiiabsorptions(withtotal
galaxy by stacking the Feii* transitions (Figure 4). We discuss rest-frameequivalentwidthsfrom3to5Å),butnoevidencefor
here(inSection7.1)theimplicationsfortheseresultsinthecon- P-cygniprofilesandgloballysmallamountsofpossibleemission
text of radiative transfer wind models, since the emitting gas is infillingasdiscussedinSection4.1.Wenextdiscusswhetherthis
likelyentrainedinagalactic-scaleoutflow. apparentlackofFeiiresonantemissionoccursinothergalaxies,
The strong, asymmetric Feii and Mgii absorptions in the andhowtopotentiallyreconcilethemodelswithsuchdata.
1D galaxy spectrum, which have blueshifted components at
LiketheHDFSID#13galaxy,thetwopreviouslypublished
−660 km s−1 and −350 km s−1 relative to the systemic redshift
direct detections of Feii* emission (Rubin et al. 2011; Martin
(Figure2),areaclearsignatureofoutflowinggas.InSection7.2,
et al. 2013) do not have Feii P-cygni profiles, although they
we will estimate the mass outflow rate and compare it to the
mighthavemoderateresonantFeiiemissioninfilling.Unlikethe
galaxySFR.
HDFS ID#13 galaxy, these galaxies have strong P-cygni Mgii
profiles.Thepublishedcompositespectra(Taliaetal.2012;Erb
7.1. Implicationsforoutflowmodels etal.2012;Korneietal.2013;Tangetal.2014;Zhuetal.2015)
shownon-resonantFeii*emissionwithoutobviousresonantFeii
The MUSE surface brightness maps (Figure 4) reveal that the emission as P-cygni profiles. Among these composite spectra,
Feii* emission has a more elliptical shape than the stellar con- only Erb et al. (2012) and Kornei et al. (2013) reveal Mgii P-
tinuumandthe[Oii]emission.DetectingFeii*emissionthatis cygniprofiles.
Articlenumber,page9of13
A&Aproofs:manuscriptno.FeII
Inordertoinvestigatetheoriginoftheapparentlackofreso- increased Feii*emission, an ISM component is essential to re-
nantFeiiemission,inFigure6wecomparerest-frameequivalent creatingtheobservationsfromthegalaxyID#13.
widthmeasurementsfromtheMUSEHDFSID#13galaxywith Finally, Prochaska et al. (2011) include dust extinction in
predictions from the Prochaska et al. (2011) radiative transfer the ISM component (orange point in Figure 6). Compared to
models,followingErbetal.(2012).InFigure6,wealsoinclude thedustywindmodeldiscussedearlier,thismodelsuffersmuch
thetwopreviouslypublisheddirectdetectionsofFeii*emission more from dust extinction because the simple kinematic struc-
from Rubin et al. (2011) and Martin et al. (2013). Each panel tureoftheISMallowsmultiplescatteringevents.ForMgii,the
pairs a non-resonant Feii* emission transition with its corre- photonsareresonantlytrappedinthedustyISM.ForFeii,allof
spondingresonantFeiiabsorptiontransitionfromwithinamul- theemissionlinesdiminishcomparedtothesamemodelwithout
tiplet. dust, but the ratio between the Feii* emission to Feii emission
Prochaska et al. (2011) produce models for the Feii UV1 remainsstrongerthaninthefiducialmodel.Thismodelbestde-
multiplet and Mgiiλλ2797,2803 doublet to explore how vary- scribes the ID#13 galaxy. Further exploring the same physical
conditionswithabi-conicaloutflowmayhighlightsubtletiesthat
ing model geometries and physical assumptions about the dust
couldindicatepreferringonegeometryoveranother.
content,ISMcontribution,gasdensity,andwindspeedsimpact
To summarize, we suggest that a model combining a dusty
thelineprofilesfromtheresonantandnon-resonanttransitions.
ISM with a bi-conical outflow that has a moderate amount of
In nearly all of the tested models, the resonant transitions pro-
dustopacityinthewindwouldbeabletomatchthedataforthe
duceP-cygniprofileswithblueshiftedabsorptionandredshifted
HDFSgalaxyID#13.
emission. Varying each of the physical properties individually
from the fiducial model is not sufficient to suppress the reso-
nantFeiiandMgiiP-cygniprofiles.Indeed,theonlymodelthat
7.2. MassOutflowRateEstimation
substantiallysuppressestheresonantemissioncombinesanISM
component with dust extinction. In order to reproduce the ob- Toestimatethemassentrainedintheoutflow,weconsideronly
served profiles of the MUSE HDFS galaxy ID#13, the models theabsorptioncomponentsthatarenotaffectedbytheISM.Con-
willneedtosimultaneouslyincorporatemoreproperties.Togain sequently,weexcludethecomponent‘C’atthesystemicveloc-
physicalintuitionfortheimpactoftheindividualproperties,we ity(Figure2,Table2).Theothertwocomponentsareblueshifted
now discuss varying the outflow geometry, dust extinction and by−660kms−1 (‘A’)and−350kms−1 (‘B’),respectively.The
ISMcomponentaffectstheprofiles. windcomponent ‘B’at −350km s−1 dominatesthe bulkofthe
massfluxgiventheequivalentwidthratiosbetweencomponents
Incontrasttotheirfiducialmodel(blackpointinFigure6),
‘A’ and ‘B.’ As discussed in Section 4.1, the wind component
which assumes angular isotropy, Prochaska et al. (2011) also
‘B’ is the least affected by emission infilling (at or below the
modeledbi-conicaloutflows(purplepoints),wherethewindfills
10%level),whereastheISMcomponent‘C’isthemostaffected
anopeningangleintoandoutoftheplaneoftheskyalongthe
by emission infilling. Hence, emission infilling does not affect
lineofthesighttothegalaxy.Collimatingtheoutflowsuppresses
ourestimateofthemassoutflowratefromthewindcomponent
both the resonant and non-resonant emission, and for highly
‘B.’
collimatedoutflows,absorptiondominatestheprofile.Thelack
SimilartoRubinetal.(2014),weestimatethemassoutflow
of resonant emission in the HDFS galaxy ID#13 suggests that
ratefrom:
theoutflowcouldbebi-conicalandcollimated.However, since
thisgeometryalsosuppressesthenon-resonantFeii*emission, dM ≈1M yr−1C Nflow(H) Aflow v 5kpc (1)
highly collimated wind models create a double-peaked Feii* dt (cid:12) f1020cm−245kpc2300kms−1 D
profilethatisnotobserved. whereC isthecoveringfractionoftheoutflowinggas,N (H)
f flow
TheProchaskaetal.(2011)fiducialmodelassumesnodust is the column density of hydrogen associated with the outflow,
extinction,buttheyshowthatdustabsorption(pinkpointsinFig- A istheprojectedsurfaceareaoftheoutflow,vistheoutflow
flow
ure 6) can have a strong impact on the line profiles. Increasing velocity,andDisthephysicaldistancetheoutflowextendsfrom
the amount of dust extinction suppresses the resonant emission thegalaxycenter.
slightlymorethanthenon-resonantemission.Addingτ = 3 WeestimateN (H)fromthemetalcolumndensitiesN(Fe)
dust flow
tothefiducialmodelleavesaweakFeiiP-cygniprofile,whereas andN(Mg).BecauseVPFITcolumndensitiesandDopplerbpa-
the model with τ = 10 suppresses the resonant Feii emis- rameters are degenerate for optically thick lines, we determine
dust
sionwhileleavingweaknon-resonantFeii*emission.However, the metal column densities N(Fe) and N(Mg) from the equiva-
suchcopiousdustextinctionwouldextinguishthesourceby15 lentwidth,W ,followingSpitzer(1968),withanadditionalterm
0
magnitudesandmakeitunobservable.Themoderatevisualex- forthecoveringfraction:
tinctionforthegalaxyID#13,A =1.20+0.59mag,suggeststhat
dust extinction alone is not suffiVcient to−e0x.2p6lain the diminished logN =logWλ0 −log2πF1/(2ττ0) −logλf −logCf +20.053 (2)
resonantemission. 0
where τ is the optical depth at line center, λ is the transition
Adaptingtheoutflowmodeltoincludegasthatrepresentsthe 0
wavelength in Å, and f is the oscillator strength. The optical
ISMofthegalaxy(redcircularpointinFigure6),i.e.,gasthatis
depthτ isdeterminedfromtheratioofequivalentwidthsfrom
centralizedandlacksasignificantradialvelocity,alsoproduces 0
two lines within the same multiplet, as in Weiner et al. (2009);
line profiles with similarities to the galaxy ID#13. Adding the
Rubin et al. (2010b), which is referred to as the ‘doublet ratio’
ISM component increases the absorption around zero systemic
velocity and suppresses the resonant Feii emission. Moreover, method.
theISMcomponentcanboosttheFeii*emission.ForFeii,more ForMgii,theoscillatorstrengthsindicatethattheequivalent
widthratiois2:1intheopticallythincase.TheMgiiequivalent
resonant absorption due to the ISM component allows more
widthratiofollowsF(2τ )/F(τ )forthetransmissionintegral:
photons to escape through non-resonant re-emission. Indeed, 0 0
the non-resonant Feii* emission becomes ∼ 10 times stronger (cid:90) +∞
than in the fiducial model. With suppressed Feiiemission but F(τ0)= (1−e−τ0exp(−x2))dx (3)
0
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