Galactic Winds and Extended Lya Emission from the Host Galaxies of High Column Density QSO Absorption Systems

0.66 MB·English

by  Luke A. Barnes

Mon.Not.R.Astron.Soc.000,1–17(2010) Printed19January2011 (MNLATEXstylefilev2.2)
Galactic Winds and Extended Lyα Emission from the Host
Galaxies of High Column Density QSO Absorption Systems
Luke A. Barnes1 ⋆, Martin G. Haehnelt2⋆, Edoardo Tescari3,4,5 and Matteo Viel3,4
1InstituteforAstronomy,ETHZurich,Wolfgan-Pauli-Strasse27,CH-8093,Zurich
2InstituteofAstronomyandKavliInstituteforCosmology,MadingleyRoad,Cambridge,CB30HA
3INAF-OsservatorioAstronomicodiTrieste,ViaG.B.Tiepolo11,I-34131Trieste,Italy
4INFN/NationalInstituteforNuclearPhysics,ViaValerio2,I-34127Trieste,Italy
1 5DipartimentodiFisica-SezionediAstronomia,Universita´diTrieste,ViaG.B.Tiepolo11,I-34131Trieste,Italy
1
0
2

n notyetsubmitted
a
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7 ABSTRACT
1 We present 3D resonant radiative transfer simulations of the spatial and spectral dif-
fusion of the Lyα radiation from a centralsource in the host galaxies of high column

] density absorption systems at z∼3. The radiative transfer simulations are based on a
O
suite of cosmological galaxy formation simulations which reproduce a wide range of
C
observedpropertiesofdampedLyαabsorptionsystems.TheLyαemissionispredicted
. to be spatially extended up to severalarcsec, and the spectral width of the Lyα emis-
h
sionis broadenedtoseveralhundred(insomecase morethanthousand) kms−1. The
p
- distribution and the dynamical state of the gas in the simulated galaxies is complex,
o the latter with significant contributionsfrom rotation and both in- and out-flows. The
tr emergingLyα radiationextendsto gaswith columndensitiesof NHi ∼1018 cm−2 and
s its spectral shape varies strongly with viewing angle. The strong dependence on the
a
centralHicolumndensityandtheHivelocityfieldsuggeststhattheLyαemissionwill
[
also varystronglywith time ontimescalesofa few dynamicaltimesofthe centralre-

1 gion.Suchvariationswithtimeshouldbeespeciallypronouncedattimeswherethehost
v galaxyundergoesamajormergerand/orstarburst.Dependingonthepre-dominanceof
9
in-orout-flowalongagivensightlineandthecentralcolumndensity,thespectrashow
1
prominentbluepeaks,redpeaksordouble-peakedprofiles.Bothspatialdistributionand
3
spectralshapeareverysensitivetodetailsofthegalacticwindimplementation.Stronger
3
galacticwindsresultinmorespatiallyextendedLyαemissionand–somewhatcounter-
.
1 intuitively–anarrowerspectraldistribution.
0
1 Keywords: quasars:absorptionlines—galaxies:formation
1
:
v
i
X
1 INTRODUCTION spondingcontinuumemissionisverycompact(Hayashinoetal.
r
a 2004; Dijkstra,Haiman,&Spaans 2006; Rauchetal. 2008;
Searches for Lyα emission that are performed down to very
Finkelsteinetal.2010).
low flux levels can detect very faint objects where the Lyα
emission is little affected by dust. Lyα emission has there- DeepLyαobservationsofthehigh-redshiftUniversethus
fore developed into an important tool to study high-redshift havetremendouspotentialtoprobethesurroundingneutralgas
galaxies(Cowie&Hu1998;Steideletal.2000;Huetal.2002; in protogalaxies, and thereby shed light on galaxy formation.
Kodairaetal. 2003; Rhoadsetal. 2004; Taniguchietal. 2005; ThespectroscopicsurveyofRauchetal.(2008,hereafterR08)
Kashikawaetal. 2006; Iyeetal. 2006; Stanwayetal. 2007; for low surface brightness Lyα emitters based on a 92 hour
Otaetal. 2008; Ouchietal. 2010). At high redshift, or for in- longexposurewiththeESOVLTFORS2instrumenthaspushed
trinsically faint objects, it is also often the only means of es- Lyα surveys to new sensitivity limitsand yielded a sample of
tablishing a spectroscopic redshift. At low flux levels, Lyα 27 spatially extended (several arcsec) low-surface Lyα emit-
emission due to star formation in galaxies can be spatially terswithfluxesof3×10−18ergs−1cm−1 andaspacedensityof
very extended due to the resonant scattering of Lyα pho- ∼3×10−2h3 Mpc−3,similartothatofthefaintestdwarfgalax-
70
tons — even if Lyα cooling is not important and the corre- iesinthelocal Universe. Basedon theinferred incidence rate
forabsorption,R08arguedthattheirsampleshouldoverlapsig-
nificantlywiththeelusivehostpopulationofDampedLyαAb-
⋆ E-Mail:[email protected](LAB) sorptionSystems(DLAs).
(cid:13)c 2010RAS
2 Barnes,Haehnelt,Tescari andViel
Barnes&Haehnelt (2009, 2010, hereafter BH09, celeration scheme, by which photons which have frequencies
BH10), building on the successful model for DLAs of close to line centre are scattered into the wings, is adapted
Haehnelt,Steinmetz,&Rauch (1998, 2000), presented a to the conditions in the current cell. We have tested and sub-
simple model that simultaneously accounts for the kinematic sequently adopted a prescription similar to that described in
properties, column density distribution and incidence rate of Laursen,Razoumov,&Sommer-Larsen(2009).Further details
DLAs and the luminosity function and the size distribution onthecodecanbefoundinBarnes(2010).
of the R08 emitters in the context of the ΛCDM model for The emergent spectrum will depend on the angle
structureformation.ThemodellingofBH10assumedspherical from which the system is viewed. Rather than “wait-
symmetry and simple power law profiles for gas density and ing” for enough photons to emerge in a given direc-
peculiar velocity. Lyα radiative transfer is, however, sensitive tion, we implement the “peeling-off” algorithm, described in
tothedetailsof thespatial distributionandvelocityof neutral Yusef-Zadeh,Morris,&White (1984) and Wood&Reynolds
hydrogen — inhomogeneity can provide channels for rapid (1999).Ateachscattering,theprobabilityofescapeinthedirec-
spatial diffusion, while bulk velocities have a similar effect in tionoftheobserveriscalculatedandasuitableweightaddedto
frequencyspace. thecorresponding2Dpixel.Thephotonsthateventuallyescape
The complicated physics of galaxy formation — gravity, the system are used to calculate the angularly-averaged spec-
hydrodynamics, radiative cooling, star formation, supernovae, trumandsurfacebrightness profile.Wehaverunstandardtest
galacticwinds,ionisingradiation,metalanddustproduction— problemstotestour3Dcodeandfoundthattheyarereproduced
has led to numerical simulations being the method of choice verywell.
forinvestigatingthephysicalpropertiesofthegasfromwhich Our modelling nevertheless has a number of significant
galaxies form. These simulations provide us with realistic 3D simplifications. We post-process the output of a cosmological
density and velocity fields that take into account most of the simulations.Thesimulationsthereforedonottakeintoaccount
relevantphysics. thedynamical effectof radiationpressure. Lyαradiationpres-
HerewewillapplytheLyαradiativetransfercodedevel- sure has been proposed to provide sufficient energy to launch
oped inBH10, adapted for the post-processing of 3D gasdis- anoutflowingsupershellforluminoussources(Dijkstra&Loeb
tributions,totheresultsofsimulationofDLAhostgalaxiesin 2009).However,thesystemsthatweconsiderheredonothave
a cosmological context by Tescarietal. (2009). We study the the necessary Lyα luminosity for radiation pressure to be dy-
effect of the spatial distributionand thekinematic stateof the namicallysignificant.Oursimulationsalsoignoretheevolution
neutral hydrogen on the low surface brightness spatially ex- ofthedensityandvelocityfieldoverthelighttraveltimeofthe
tendedLyαemission,whichshouldbecomeanimportantprobe Lyαphotons.Wefurtheronlyconsideraverycentrallyconcen-
ofkinematicsofthegasinDLAhostgalaxies. tratedemissivity.Forsimplicityweinjectphotonsatthecentre
In this first paper we will focus on a detailed investiga- of mass of the halo. The photons are created with line-centre
tion of a small number of such simulated systems. In Section frequency in the fluidframe of the gas. We will discuss these
2,wedescribethe(minor)changestoourLyαradiativetrans- assumptionsfurtherinSection5.1.
fercodeneededtofollowphotonsthroughadensitydistribution
ona3Dgrid.InSection3.1,wedescribethesetofsimulations
of Tescarietal. (2009) that we have used, and in Section 3.2
3 LyαRADIATIVETRANSFERINDLAHOST
we describe the three haloes that we have extracted from the
GALAXIES
simulationsforfurtherstudy.Section4discussesthehaloesin
detail,lookingparticularlyattheeffectofgalacticwindsonthe 3.1 TheSimulationsofDLAhostgalaxiesina
gaspropertiesandLyαemission.WediscussourresultsinSec- cosmologicalcontextbyTescarietal.
tion5,includingtheirrelevancetoobservedpopulationsofhigh
Wewillmakehereuseofthecosmologicalhydrodynamicsim-
redshift Lyα emitters, including LBG’s, before presenting our
ulations described in Tescarietal. (2009). These simulations
conclusionsinSection6.
were aimed at reproducing the physical properties of the host
galaxiesofDLAsatz∼3.Thenumericalcodeisamodification
of gadget-2, which isaparallel Tree-PMSPHcode (Springel
2 THE3DLyαRADIATIVETRANSFERCODE 2005). The code is extensively described in Tornatoreetal.
(2007),whereitwasusedtosimulateclustersofgalaxies;see
3D Lyα cosmological radiative transfer of Lyα radiation has
alsoTornatoreetal.(2010)andTescarietal.(2010).Inaddition
been studied by a number of authors (Cantalupoetal. 2005;
togravityandhydrodynamics,theotherphysicalprocessesthat
Tasitsiomi2006;Laursen,Razoumov,&Sommer-Larsen2009;
aremodelledinthesimulationare:
Zhengetal.2009;Kollmeieretal.2010;Faucher-Gigue`reetal.
2010),inthecontextof,forexample,fluorescentemissionfrom • Radiativecoolingandheating,includingaUVbackground
the IGM, bright Lyα emitters at z≈8, young Lyman break producedbyquasarsandgalaxies.
galaxiesandLyαemissionlinkedtoradiativecooling. • Chemical evolution, using the model of Tornatoreetal.
Wehavepreviouslydescribedourimplementationofa1D (2007)whichtracesthefollowingelements:H,He,C,O,Mg,S,
Lyα radiative transfer algorithm in BH10. In short, Lyα pho- SiandFe.Thecontributionofmetalsisincludedinthecooling
tons are created according to the emissivity profile, and then function.ThereleaseofmetalsfromTypeIaandTypeIIsuper-
propagatedthroughthegas.Eachtimethephotonisscattered, novae,aswellaslow-andintermediate-massstars,isfollowed.
a new frequency is calculated by assuming that the photon’s • Starformation,usingamultiphasecriterion.
frequency in the scattering atom’s frame is unchanged. Thus, • AneffectivemodelfortheISM,wherebygasparticlesare
the code tracks the random walk in both real and frequency treatedasmultiphaseoncetheyexceedadensitythresholdfor
spacebeforethephotonescapesandisobserved.Thenewcode theformationofcoldclouds.Thesecoldcloudsaretheprecur-
used here follows photons through a regular 3D grid. The ac- sorstostars.TheneutralhydrogenfractiondependsontheUV
(cid:13)c 2010RAS,MNRAS000,1–17
GalacticWindsandExtended LyαEmission 3
background in the low density gas, and on the fraction fc of where vc ∝ M1/3 is the virial velocity of the halo. With this
massincoldcloudsabovethedensitythreshold. choice BH09 and BH10 were able to reproduce the luminos-
• Galactic winds, using two different prescriptions. An ityfunctionoftheR08emitters.Themassesofthethreehaloes
energy-drivenwindmodelisimplementedintheformofafixed probetherangeofmassespredictedtocontributesignificantly
velocity kick given to achosen particle, with a mass-loss rate to the incidence rate of DLAs / emitters per unit log mass
proportionaltothestarformationrate.Tescarietal.(2009)also (d2N/dX/dlog M).Thecorresponding luminositiesspanthe
10
investigatedamomentum-drivenwindmodelthatmimicsasce- rangeofthoseobservedinthesurveyofR08.
nario in which the radiation pressure of a starburst drives an Thephysicalpropertiesofthesehaloes(neutralhydrogen
outflow.Inthismodel,thevelocitykickscaleswiththevelocity density, temperature and bulk velocity) were projected onto a
dispersion of the galaxy. These wind prescriptions are admit- regular3Dgridcentredonthecentreofmassofthehalo.The
tedly rather crude, and rely on phenomenological parameters cubescontainingHaloes1and2have1283cells,eachwithside
that are poorly constrained either by observations or by more length3.125h−1comov.kpc,makingtheentirecube400h−1co-
sophisticatedmodelling.Thisreflectsthesignificantuncertainty mov.kpcacross.ThecubecontainingHalo3has643cells,each
regardingtheinfluenceofwindsongalaxyformation. also3.125h−1 comov.kpcacross,makingthewithoftheentire
cube200h−1comov.kpc.
Tescarietal.(2009)investigatedsimulationswithvarying
WewillfirstexaminethesimulationwiththeMDWimple-
box size and numerical resolution for a range of different im-
mentation of galactic winds, before comparing with the other
plementationsofgalacticwinds.Theychosethe“SW”(Strong
simulations in later sections. Figure 1 shows the angularly-
Wind)simulationwithaboxsizeof10h−1Mpcand3203 parti-
averagedradialmassflowrate,projectedcolumndensityofneu-
cles,withamassresolutionof3.5×105h−1M⊙astheirfiducial tral hydrogen and the Lyα surface brightness as a function of
simulation. Thissimulation employed astrong(600 km s−1), radius/impactparameteraswellastheangularly-averagedspec-
energy-driven windandaSalpeterstellarIMF.Lookingahead
tralshapeoftheLyαemissionforthethreehalos.
toafavourablecomparisonwiththeR08emittersinalatersec- TherateatwhichHimassflowsthroughasurfaceofcon-
tion,wewillinsteadfocusmoreontheMomentumDrivenWind
stantradiusrisshownintheupperleftpanelofFigure1,nor-
(MDW)simulation,whichdiffersfromtheSWsimulationonly malisedtoamaximum|M˙|=1.Positive(negative)valuescor-
inthewindimplementation.Wewillcomparetheresultsofboth respondtooutflow(inflow).ThemaximumM˙ is97,8.5and1.5
the MDW and SW simulation with two further simulations: a
weak(energydriven, 100 kms−1) wind(WW)andasimula- M⊙/yr,forHalo1,2and3respectively.Notethat,fortheMDW
implementationshownhere,onlyinthemostmassivehalodoes
tionwithnowind(NW)whichdidnot appear inTescarietal.
the windactually manage to globally reverse the gravitational
(2009).Aswewillsee,theMDWandtheSWsimulationsare
infall. The mass flow shows a mixture of inflow and outflow,
somewhatsimilar,asaretheWWandNWsimulations.
withinflowoftendominatingintheouterpartsofthehalo.
The simulations of Tescarietal. (2009) reproduce most
Theupper rightpanel ofFigure1showstheaveragecol-
observed properties of DLAs rather well. The observed inci-
umn density for a sightline passing at a given impact param-
dence rate of DLAs is matched by the simulations, assuming
eter from the centre of the halo. The thin dotted horizontal
thathaloesbelow109h−1M⊙ donothostDLAs.Theobserved lineindicatestheminimumcolumndensityofaDLA,N =
DLA
columndensitydistributionisalsoreproducedsuccessfullyfor 1020.3 cm−2. As expected, the column density peaks near the
theSWandMDWsimulations,whilethetotalneutralgasmass
centre of the halo. The “steps” in the column density profiles
in DLAs (ΩDLA) is reproduced for MDW but underpredicted ofHaloes2and3showtheinfluenceofseparateclumpsofHi
by a factor of about 1.7 at z=3 in the SW simulation. The
atlargeradii.Theneutralhydrogencolumndensityexceedsthe
most problematic observable isthe velocity widthdistribution
thresholdforaDLA,whichextendstoaradiusof3.5,1.5,and
oflow-ionizationassociatedmetalabsorption.Thehighveloc-
0.5arcsec,respectively.
itytail of thedistributionissignificantly underpredicted inall
The lower left panel shows the (observed) angularly-
simulations. The simulations do not produce enough absorp-
averaged spectrum, with each curve normalised to unity. The
tionsystemswithvelocitywidthgreaterthan100 kms−1.This
lowerrightpanelshowsthesurfacebrightnessprofile.Thelumi-
is a common problem for numerical simulations of DLA host
nosityusedtonormaliseeachcurveisgiveninthelastcolumn
galaxies (Pontzenetal. 2008; Razoumovetal. 2008), but see
ofTable1.
Hongetal. (2010) and Cen (2010) which appear to be some-
The surface brightness profiles peak at the centre of the
whatmoresuccessfulinthisrespect.Wewillcomebacktothis
halo, and generally follow the decline of the column density
pointlater.
whilstbeingmuchsmoother.TheLyαemissionisscatteredto
similarlylargeradiiasintheobservedemitters.Thehaloesare
surrounded by low surface brightness emission which extends
3.2 Threerepresentativehaloes toradiiofseveral arcsec.Thesizeoftheemitter,asmeasured
tothesurface brightness limitof theR08 (shown by thehori-
Wehaveselectedthreehaloesatz=3fromthesimulationsfor
zontaldottedline),isgenerallylargerthanthecross-sectionfor
detailed study. Some basic properties of the haloes are sum-
dampedabsorption.Themoremassivehaloesaremorespatially
marisedinTable1.Thevirialvelocityandradiusarecalculated
extended,whilethesmallerhaloesdisplayamorepronounced
fromthemassoftheparticlesgroupedbythehalofinder—see
centralpeak.
Maller&Bullock (2004) for the relevant formulae. Note that
Theangularly-averagedspectrumofthemostmassivehalo
thepropertiesofagivenhaloforthedifferentwindmodelsimu-
isfairlysymmetricwithwellseparatedblueandredpeaks.The
lationsareverysimilar.ThefinalcolumnliststheLyαluminos-
redpeak isslightlystronger. Thetwolow masshaloes have a
ity(L ),calculatedfollowingBH09andBH10as,
Lyα moreclearlydominantredandbluepeak,respectively.Increas-
LLyα=1042(cid:18)100kvmc s−1(cid:19)3 ergs−1 (1) ifnregquceennctryalspcaoclue.mWnedewnisllitsyeeclienartlhyelneeaxdtssteoctmioonrethdatiffthuesiospnecin-
(cid:13)c 2010RAS,MNRAS000,1–17
4 Barnes,Haehnelt,Tescari andViel
Halo Wind Mass MassHi VirialVelocity VirialRadius LyαLuminosity
ID Model (M⊙) (M⊙) ( kms−1) (kpc) (arcsec) (×1040ergs−1)
1 momentum(MDW) 7.70×1011 2.03×1010 206.7 77.5 9.8 882.7
strong(SW) 7.24×1011 1.38×1010 202.5 76.0 9.6 830.9
weak(WW) 8.15×1011 2.80×1010 210.7 79.0 10.0 935.3
none(NW) 8.12×1011 2.00×1010 210.4 78.9 10.0 931.5
2 MDW 1.54×1011 3.36×109 120.9 45.3 5.8 176.5
SW 1.40×1011 1.07×109 117.2 43.9 5.6 160.8
WW 1.70×1011 6.22×109 125.0 46.9 5.9 195.1
NW 1.65×1011 4.76×109 123.7 46.4 5.9 189.3
3 MDW 1.46×1010 2.74×108 55.1 20.7 2.6 16.7
SW 1.36×1010 1.30×108 53.8 20.2 2.6 15.6
WW 1.58×1010 8.10×108 56.6 21.2 2.7 18.2
NW 1.57×1010 9.12×108 56.5 21.2 2.7 18.1
Table1.CharacteristicpropertiesofthreeDMhaloesofDLAhostgalaxies.
1
Halo1 2]
−
Halo2 m
Halo3 [c 20
/y[Mr]sun 0.05 mndensity 18
dt u
/M Col
d -0.5 HI 16
g
o
l
-1 14
0 2 4 6 8 0 2 4 6 8
radius[arcsec] impactparameter[arcsec]
-16
2 ]
2c
−1/[kms] 1.5 2/marcse -18
3×P10v 1 //S[ergsc -20
g
0.5 lo
-22
0
-1000 -500 0 500 1000 0 2 4 6 8
vph[km/s] impactparameter[arcsec]
Figure1.Theangularly-averaged properties ofthethreeDLAhostgalaxiesdescribedinTable1,fortheMDWwindmodel.Theupperleftpanel
showsdM/dt,whichistherateatwhichHimassisflowingthroughasurfaceofconstantradiusr,normalisedtoamaximum|M˙|=1.Themaximum
M˙ (bywhichthecurvearescaled)are97,8.5and1.5M⊙/yr,forHalo1,2and3respectively.Theupperrightpanelshowstheaveragecolumndensity
forasightlinepassingatagivenimpactparameterfromthecentreofthehalo.Thethindottedhorizontallineindicatestheminimumcolumndensity
ofaDLA,NDLA=1020.3cm−2.Thelowerleftpanelshowsthe(observed)angularly-averagedspectrum,withtheareaundereachcurvenormalisedto
unity.Thelowerrightpanelshowsthesurfacebrightnessprofile;thehorizontallineshowsthesurfacebrightnesslimitoftheR08survey.Theassumed
totalLyαluminosities(whichnormaliseeachcurve)aregiveninthelastcolumnofTable1.
tralshapevariesstronglybetweendifferentdirectionsandthat 4 THEEFFECTOFGALACTICWINDSONLyα
thereisacorrelationbetweenthedominanceofinflow(outflow) EMISSION
andthedominationoftheblue(red)peakinthespectrum.We
willleaveamoredetaileddiscussionuntilthen.
Wewill now discuss the simulations of the intermediatemass
halo(ourfiducialHalo2)inmoredetailwithparticularempha-
sisontheeffectofgalacticwindsonthephysicalpropertiesof
the gas in the halo and on the emission properties of the Lyα
emission.Halo2hasamassofabout1.5×1010M⊙andavirial
(cid:13)c 2010RAS,MNRAS000,1–17
GalacticWindsandExtended LyαEmission 5
velocity of about 120 km s−1. Itsproperties aresimilar tothe dM/dt=4πr2vHi(r)ρaHvi(r),whereρaHvi istheaverageneutralhy-
brightest of theemittersintheR08 survey, and itsmasscoin- drogendensityatradiusr.Noticethattheflowsintheinnermost
cides withthe peak of our preferred model for theDLAmass partsofthehalo,whilebeingofmodestvelocity,carrythemost
function(d2N/dX/dlog M)fromBH10andthusshouldrep- significantamountsofmass.
10
resentatypicalDLAhostgalaxy. Comparison of vHi(r), vV and dM/dt is quite instructive.
Therelativesmoothnessofv indicatesthatasmallnumberof
V
denseclumpsdominatethemassflow,moving througharela-
4.1 Angularly-AveragedProperties tivelysmoothbackgroundwhosekinematicsareshapedbythe
winds. For example, the MDW model (solid black) shows a
Angularly-averaged properties of simulation based on Halo 2 ∼100 km s−1 inflowing clump at 2 arcsec that carries a sig-
foreachofthewindmodelsareshowninFigure2.Thelegend nificantamountofmass.However,v isstillpositive,showing
V
inthetoprightpanelshowstheline-stylesofthedifferentwind thatthewindisfillingtheremainingspaceandoutflowingre-
models gardless.Lyαphotonsescapingalonglowcolumndensitypaths
ThetopleftpanelshowstheHinumberdensityasfunction willgenerallynot“see”suchdenseclumps.
ofradius.Notethattheaveragecosmicnumber densityofhy- The panel to the right shows the rotation velocity of the
drogenatz≈3is1.2×10−5cm−3,whilethevolume-averaged gas,averagedovercylindricalshells,whichisapproximatedas
neutralfractionofhydrogenintheIGMis.10−5.Asmallde- follows.Ifthegasinthehalowereinarotatingdiskwitharota-
crease inthe number density at small radii isthe result of the tionvelocitydependingonlyonthecylindricalradius,thenthe
centre of mass of the neutral hydrogen being offset from the angular momentum within a cylindrical shell R,R+dR would
centre of mass of the halo. The number density profile shows be,
theeffectofseveralclumpsofHi.Themostdramaticdifference
between the models is in the centre of the haloes, where the |Lrot|=vrot(R)RXmi, (3)
presence of astrong windcanreduce thegasdensity substan- i
tially. wherethesumisoverthecellsinsidetheshell.Thusforeach
Thetoprightpanelshowstheaveragedcolumndensityfor R,wedividetheangularmomentumbyRtimesthemassinthe
a sightline passing at a given impact parameter from the cen- shell.AswithvHi(r),thisdistributionisfarfromsmoothdueto
tre of the halo. The thin dotted horizontal line indicates the theinfluenceofdenseclumpsofgas.Thevelocitydropsfrom
minimum column density of a DLA. The column density isa ∼150 kms−1 to∼50 kms−1 aswemoveoutwards.Theve-
decreasingfunctionofradius,withsightlinescontainingDLAs locityisgenerallyhigherintheweaker windmodels,possibly
probingthecentreofthehalo.The“clumps”noticeableinthe indicatingthatthestrongerwindsdisruptordelaythesettlingof
number densitydistribution, causestepsintheangle-averaged gasintoadisk.Wecanalsocalculatethefractionofthekinetic
columndensitydistributionandcontributetotheLyman-Limit energyateachradiuswhichisintheformofrotationalkinetic
Systemcross-section. energy. This quantity peaks at ∼0.7 at the centre of the halo,
Thenextpanel(row2,column1)showsthe(Hi)density- decreasing to∼0.2inthe outer parts. Thisshows that theap-
weightedradialvelocityprofile, proximations wemade incalculating vrot are most accurate at
thecentreofthehalo,asexpected.
vHi(r)≡hub·ˆri≡ R02πRR002ππR(0uπb·ρˆrH)i(ρrH,θi(,rφ,)θs,φin)θsidnθθddφθdφ. (2) tsrpuemct.TruohmfetbahosettaoLmfyuαnleceftmitopinsasnoieoflnt.shheTohrweessttt-hhfirecakmanebgluvalceaklrolcyci-utayrvveoerffassgheeotdw(vssptehc≡e-
ph
Theplotrevealsthepresenceofamixtureofinflow(vrnegative) c∆λ/λ0). All curves are normalised to have unit area. The
andoutflow,withtheinnermostpartsofthehalotendingtoshow weaker wind models show a classic double-peaked profile
outflowforthestrongerwinds(SWandMDW),andinflowfor (Harrington 1973; Neufeld 1990; see also Urbaniak&Wolfe
theweakerwinds(WWandNW). 1981),whilethestrongerwindmodelsshowamoreprominent
Thetypicalvelocitiesofinfloware50-100 kms−1,with redpeak,indicatingtheinfluenceoftheoutflowinggas.
the largest velocities being comparable to the virial velocity. Wealsoseethatthestrongergalacticwinds—somewhat
Thereisageneraltrendtowardlowervelocitiesinthecentreof counterintuitively — result inanarrower spectral distribution.
thehalo.Thevelocityprofileis,however,farfromsmooth.The This indicates that it is the high central column density, more
total velocity of the gas (v= h|u |2i), by comparison, varies thanthehigheroutergasvelocities,thatarethedominantfactor
b
between100-150 kms−1forthpestrongerwinds,and140-200 inestablishingthetypicalescapefrequencyofLyαphotons.
kms−1 fortheweakerwinds,withaveryslightpreferencefor Thethickblackcurveinthebottomrightpanelshowsthe
largervelocitiesatthecentreofthehalo. angularly-averaged surface brightness profile. The luminosity
The panel to the right shows the volume-weighted ra- thatnormaliseseachcurveisgiveninthelastcolumnofTable1.
dial velocity profile (vV). For the diffusion of Lyα photons, Theverticallineindicatesthevirialradiusofthehalo,whilethe
volume-weighted velocities are actually more relevant than horizontal lineshowsthesurfacebrightness limitofR08.The
density/mass-weighted velocities as the photons tend to find surfacebrightness profileshowsacentralpeak withatailthat
low-density paths of escape, and so the velocity in the under- flattensoutasthecolumndensitydoesthesame.Theemission
denseregionsisasimportantormoreimportantasthatinhigh- is more extended in the stronger wind models. There are two
density regions. We see a clear difference in v between the reasons for this. Thelower central column density means that
V
strongerandweakerwindmodels.Thestrongwindmodelshave photonsareingeneralclosertolinecentrewhentheyencounter
outflowsthatdominatethekinematicsofthegasalongmostof theouterpartsofthehalo,wherehigherwindvelocitiescanshift
theescapepathsofthephotons.Forweakwindmodels,inflow thephotonssufficientlybacktowardslinecentretobescattered
dominates.Thenextpanel(row3,column1)showsdM/dtfor byratherlowcolumndensitygas.Comparingtheradialprofile
Hi, which isrelated to the density-weighted radial velocity as ofHicolumndensityandLyαsurfacebrightnessforthediffer-
(cid:13)c 2010RAS,MNRAS000,1–17
6 Barnes,Haehnelt,Tescari andViel
0
−3m] −2m] 22 MDW
replacement[cs [c 21 SW
density -2 density 20 WNWW
mber -4 umn 19
nu Col
HI HI 18
log -6 log 17
16
0 2 4 6 8 0 2 4 6 8
radius[arcsec] impactparameter[arcsec]
/ms] 100 /ms] 250
k
[ k 200
wgt.) 50 gt.)[
w 150
(dens. 0 (vol. 100
velocity -50 velocity 50
radial -100 radial 0
-150
-50
0 2 4 6 8 0 2 4 6 8
radius[arcsec] radius[arcsec]
200
5
s]
r] 0 /m 150
/y [k
Msun -5 city
dt[ -10 velo 100
/M n
o
d -15 ati
-20 rot 50
-25
0
0 2 4 6 8 0 2 4 6 8
radius[arcsec] radius[arcsec]
-16
2
]
2c
−1/ms] 1.5 2/arcse -18
k m
[ c
3×10 1 //ergs
Pv S[ -20
g
o
0.5 l
0 -22
-1000 0 1000 0 2 4 6 8
vph[km/s] impactparameter[arcsec]
Figure2.Angularly-averaged propertiesofHalo2,forthewindprescriptionsasshowninthelegend(MDW:momentumdrivenwind,SW:strong
wind,WW:weakwind,NW:nowind).ThevelocitiesanddM/dtareallforHi.Verticaldashedlinesindicatethevirialradius.Foradetaileddiscussion,
seeSection4.1.
(cid:13)c 2010RAS,MNRAS000,1–17
GalacticWindsandExtended LyαEmission 7
entwindmodelssuggestthatthisismoreimportantthanthethe hydrogen distribution. Inparticular, the S contour encloses a
0
Hicolumndensityintheouterpartsofthehalo. much larger area than the DLA contour both by being larger
Wehavenotplottedthe(Hiweighted)temperatureprofile, andalsobyhavingfewer“holes”.TheLyαphotonsarescattered
whichforallmodelsdecreasesgentlywithradiusfromaround effectivelyouttolargeradiiandlowercolumndensities.TheS
0
105K to 104.3 K.The central temperature isslightlyhigher in contourinthesurfacebrightnessisroughlysimilartothatofthe
theweakwindmodels. NHi∼1018cm−2contour2intheHicolumndensityplot.
We can now compare the properties of the haloes to the OurcentralLyαsourceisabletoilluminatecloudsofneu-
modellingofBH10.Unlikeinourpreviousanalyticalmodelling tralgasthataredetachedfromthecentralclump.TheLyαpho-
the column density in our simulations here has a pronounced tonstendtofindlow-densitypathsofescape.Forexample,the
coreatverysmallradii.Atlargerradiitheradialprofileofthe photons face a column density of Hi which is on average ∼7
Hi column density in the MDW model appears rather similar times larger in the −z direction than in the +z direction, and
even though much larger samples of simulated haloes would the corresponding observed Lyα flux is on average ∼3 times
be needed to make a more meaningful comparison; we refer smaller.Forthe xdirection,asshownintheFigure,thediffer-
thereadertoTescarietal.(2009)foraquantitativecomparison ence in the observed flux between two opposite viewpoints is
withtheobservedDLAcolumndensitydistribution.Theradial around70%.
velocityprofilesinourfullcosmologicalsimulationsareobvi- The bottom four panels are 2D spectra, calculated us-
ously much morecomplex than thesimplepower lawprofiles ing a “slit” placed along either the y- or z-direction (labelled
wehadassumedinourpreviouswork,althoughthereisaslight in the vertical axis) and with a width of 2 arcsec, the same
trend toward lower velocities at the centre of the halo. There width as used in Rauchetal. (2008). The contour shows the
wasobviouslyalsonopossibilitytoaccountforthe3Deffects spectral intensity limit of the R08 survey, Sλ ≈ 4×10−20
ofanyclumpinginourprevious1Dmodelling. erg/s/cm2/arcsec2/Å.
The2D spectrashow adominant bluepeak inthe−xdi-
rection, and the opposite trend when viewed from+x;see the
4.2 2DViewsoftheHalo discussionofFigure4below.Asexpected,theseparationofthe
Figure3showsmapsoftheHicolumndensitydistributionand peaksislargestwherethecolumndensityislargest.Thedom-
Lyαsurfacebrightnessand2DspectraforHalo2fortheMDW inanceofonepeakovertheothertendstoincreaseaswelook
modellookingalongthex-axisfrom−∞(left)and+∞(right). awayfromthecentreofthehalo.Thisismostlikelybecausethe
probabilityofaphotonscatteringintheouterpartsofthehalo
Notethatsomeoftheaxeshavebeenflippedsothattheleftand
isquitesensitivetothevelocityofthegas.
right columns have their axes pointing in the same direction.
Thedashedblackcurveshowsthevirialradius. We illustrate the dependence of the emergent spectrum
The top panels show the Hi column density along a line and surface brightness profile on the viewing angle in Figure
ofsightparalleltothe x-axis.Eachpanelcorrespondstoaline 4,whichalsoshowstheangularly-averaged value(thickblack
line).Thethincolouredlinesshowtheemergentspectrum(cal-
ofsightthatpassesthroughthenearerhalfofthebox.Inother
culated by collapsing the slit along its spatial direction, or by
words,thecoloursinthelegendtotherightofeachFigurerep-
resent the column density of neutral hydrogen that thephoton averagingoverthe2Dimage) for6differentviewpointsalong
the principal axes. Remember that the observer sees only one
(emittedatthecentreofthehalo) would havetopassthrough
ofthesespectra-theangularly-averagedquantitiesarenotob-
ifitweretoreachtheobserverdirectlywithoutanyscattering.
The solid line in the top two panels is a contour representing servable.Thespectrashowsignificantvariations,bothinwhich
N =1020.3 cm−2,calculatedforsightlinespassingthrough peakdominatesandintotalamountoflightobserved.Thesep-
DLA
arationofthepeaksshowsrelativelylittlevariationandthesur-
theentirebox;itisthusthesameintheleftandrighttoppanels.
Asightlinepassingthroughtheregioninsidethecontourwould facebrightnessprofilesareverysimilar,especiallyintheouter
partsofthehalo.
encounteraDLA.
Thecolumn density distributionreflectstheirregular dis-
tributionofgas,withamixtureofthinfilamentsandrelatively
isolated clumps of neutral hydrogen. The differences between 4.3 Haloes1and3
thepanels show theasymmetry inthedistributionof gas.The
Theangularly-averagedpropertiesofHalo1areshowninFig-
cross-sectionfordampedabsorptioniscomposedofalargecen-
ure5.Thepanelsshowthevolume-averagedradialvelocitypro-
tralclumpaccompanied byanumberofisolatedclumps,scat-
file, projected column density of neutral hydrogen, the emer-
teredaroundthehalo.Thecolumndensityofindividualclumps
of neutral hydrogen drops rapidly below ∼1017 cm−2, due to gentLyαspectrumandtheLyαsurfacebrightnessasafunction
ofradius/impactparameter.Thefourdifferentwindmodelsare
theeffectoftheionisingUVbackgroundonparticlesbelowthe
shownoneachplot.
‘coldcloud’threshold.
Theradialvelocityprofileshowstheeffectoftheoutflow-
The next two panels show an image of the halo that is
ing winds in the low density gas. The winds provide escape
coloured according to thesurface brightness of theLyα emis-
sion, calculated1 assuming the luminosity as described pre- pathsfilledwithgasthatisoutflowingat∼100−150 kms−1,
viously and given in Table 1. The solid contour represents
the surface brightness limit of the R08 survey, S = 10−19
0
erg/s/cm2/arcsec2. 2 Varying between ∼ 1017−1019 cm−2. Note that this is not the
Thesurface brightness maps show that theLyα emission same as the mean integrated column density along the final escape
generallytracesbutislessclumpythantheunderlyingneutral flight of the photon, which we have also calculated explicitly us-
ing our code and which can be approximated analytically by Nesc≈
1020cm−2(vpeak/500kms−1)2,wherevpeakisthepeakoftheemission
1 Seeequation(20)ofLaursen,Razoumov,&Sommer-Larsen(2009). spectrum.
(cid:13)c 2010RAS,MNRAS000,1–17
8 Barnes,Haehnelt,Tescari andViel
Viewpoint:x=-∞ Viewpoint:x=+∞
23 23
8 8
22 22
6 6
21 21
4 20 ] 4 20 ]
2 2
− −
arcsec] 02 1189 N[cmHI arcsec] 02 1189 N[cmHI
[ [
z 17 g z 17 g
-2 lo -2 lo
16 16
-4 -4
15 15
-6 14 -6 14
-8 13 -8 13
8 -8 -6 -4 -2 0 2 4 6 8 8 -8 -6 -4 -2 0 2 4 6 8
y[arcsec] -16 y[arcsec] -16
6 6
] ]
-172c -172c
4 cse 4 cse
z[arcsec] -022 ---2110982///[ergscmar z[arcsec] -022 ---2110982///[ergscmar
S S
-4 -21 og -4 -21 og
l l
-6 -22 -6 -22
-8 -23 -8 -23
-8 -6 -4 -2 0 2 4 6 8 -8 -6 -4 -2 0 2 4 6 8
y[arcsec] y[arcsec]
-17 -17
8 8
6 -18 Å] 6 -18 Å]
4 -192/ec 4 -192/ec
cs cs
sec] 2 -202/mar sec] 2 -202/mar
y[arc -20 --2221 //[ergsc y[arc -20 --2221 //[ergsc
λ λ
S S
-4 -23 g -4 -23 g
o o
l l
-6 -24 -6 -24
-8 -25 -8 -25
8 -1500-1000-500 0 500 10001500 -17 8 -1500-1000-500 0 500 1000 1500 -17
6 vph[km/s] -18 Å] 6 vph[km/s] -18 Å]
4 -192/ec 4 -192/ec
cs cs
sec] 2 -202/mar sec] 2 -202/mar
z[arc -20 --2221//[ergsc z[arc -20 --2221//[ergsc
λ λ
S S
-4 -23 g -4 -23 g
o o
l l
-6 -24 -6 -24
-8 -25 -8 -25
-1500-1000-500 0 500 10001500 -1500-1000-500 0 500 1000 1500
vph[km/s] vph[km/s]
Figure3.2DimagesandspectraforHalo2intheMDWsimulation.Theleft(right)columnisasviewedfromx=−∞(+∞).Theuppertwopanelsshow
theHicolumndensityforthecloserhalf ofthesimulationbox.Thedashedcircleshowsthevirialradius.ThecontourrepresentsNDLA=1020.3cm−2,
forasightlinepassingthroughtheentirebox.ThenexttwopanelsshowtheobservedLyαsurfacebrightness.Thecontourshowsthesurfacebrightness
limitoftheR08survey,S0=10−19erg/s/cm2/arcsec2.Thelowerfourpanelsshow2Dspectra,calculatedusinga“slit”placedalongeitherthey-or
z-direction(labelledintheverticalaxis)andwithawidthof2arcsec,whichisthesamewidthasinRauchetal.(2008).Thecontourshowsthespectral
intensitylimitoftheR08survey(Rauch,M.,privatecommunication),whichisSλ≈4×10−20erg/s/cm2/arcsec2/Å.TheFigureisdiscussedfurtherin
Section4.2.
(cid:13)c 2010RAS,MNRAS000,1–17
GalacticWindsandExtended LyαEmission 9
4
Viewpoint ] -16
x=−∞ 2ec
−31/0[kms] 23 yyzx====−+−+∞∞∞∞ 2///gscmarcs -18
×1 z=+∞ [er
Pv gS -20
1 lo
0 -22
-500 0 500 0 2 4 6 8
vph[km/s] impactparameter[arcsec]
Figure4.Theemergentspectrum(left)andsurfacebrightnessprofile(right)forHalo2,showingtheeffectoftheviewingangle.Thethickblackline
istheangularly-averagedspectrum,whichisthesameasinFigure1.Thethincolouredlinesshowtheemergentspectrum(calculatedbycollapsingthe
slitalongitsspatialdirection,orbyaveragingoverthe2Dimage)forthe6differentviewpointsasshowninthelegend.TheFigureisdiscussedfurther
inSection4.2
200
/kms] 150 −2m] 22
vol.wgt.)[ 10500 density[c 2201
y( mn 19
ocit 0 olu MDW
alvel -50 HIC 18 SWWW
radi log 17 NW
-100
16
0 2 4 6 8 0 2 4 6 8
radius[arcsec] impactparameter[arcsec]
1
-16
]
0.8 2ec
−1/ms] 0.6 2/marcs -17
30[k //gsc -18
×1 0.4 [er -19
Pv S
g
o
0.2 l -20
0 -21
-2000 -1000 0 1000 2000 0 2 4 6 8
vph[km/s] impactparameter[arcsec]
Figure5.Angularly-averagedpropertiesofHalo1,forthewindprescriptionsshowninthelegend(upperleft),asdiscussedinSection4.3.Theupper
leftpanelshowsthevolume-averagedradialvelocityprofile.TheupperrightpanelshowstheHicolumndensityasafunctionofimpactparameter.
Thelowerleftpanelshowsthespectra,normalisedtounitarea.Thelowerrightpanelshowsthesurfacebrightnessdistributionasafunctionofimpact
parameter.
whileintheweakerwindcasestheaveragevelocityiscloserto smoother thanthatofHalo2and3,andasexpectedtheDLA
zero3. crosssectionissignificantlylarger.Onceagainweseethatthe
The column density profile of Halo 1 is somewhat windshaveloweredthecentralcolumndensityofthehalo.
3 Thefactthatthevolume-averagedradialvelocityisslightlypositive
intheno-windsimulation ismostlikely duetothecentreofmassof baryonshaveovershotthebottomofthepotentialwell.Heatingofthe
the baryons being offset from the centre of mass of the halo i.e. the hot,rarefiedISMbytheUVBmayalsocontribute.
(cid:13)c 2010RAS,MNRAS000,1–17
10 Barnes,Haehnelt,Tescari andViel
For Halo 1 the spectra show again the classic double- higher outflow velocitieson theLyαemission depends on ex-
peaked profile with a general trend toward domination of the actlyhowthevelocitywouldbeincreased.Ifthebulkvelocity
redpeakforhaloeswithstrongerwinds.Thesurfacebrightness inthecentreofthehaloisincreased,thenthiswouldaccelerate
profilesarerathersimilar:theypeakatthecentre,anddecrease frequency-space diffusionresultinginamorecentrallypeaked
smoothlyasthecolumndensitydrops.Theweakerwindmod- surfacebrightnessprofile.Ontheotherhand,ifthebulkveloc-
elsareasexpectedmorecentrallypeakedthanthestrongerwind ityisincreasedprimarilyintheouterpartsofthehalo,thenthis
models. wouldhaveaminimaleffect,perhapsshiftingphotonsbackto-
Theangularly-averagedpropertiesofHalo3areshownin wardline-centreandtherebyincreasingtheapparentsizeofthe
Figure6.Thegasinthestrongerwindmodelsismoreextended. emitter.
Volume-weighted all of the models aredominated by infall at Wehavealsonotattemptedtomodeltheeffectsofduston
smallradii,withonlytheSWmodelshowingaverymildout- theLyαradiation.DLAsareknowntobeamongthemostmetal-
flowatlargeradii.TheMDWwindclearlydecreasestheaverage poorsystemsinthehighredshiftuniverse,andarethusexpected
infallrate,butnottotheextentthattheinfallisreversed. to be relatively dust free(Pontzen&Pettini2009), apart from
The angularly-averaged spectrum of Halo 3 is a particu- perhapsthemostmetal-richsystems(Fynboetal.2010a,b).The
larlyniceillustrationofinflowinggasatthecentreofthehalo longrandomwalkofatypicalLyαphotonmakesthemparticu-
producingamoreprominentbluepeakinthespectrum.Inspite larlysusceptibletoevenasmallamountofdust.
ofthis,thereareviewinganglesforwhichthespectrumisdom- Anotherworrycouldbeouruseofarathercoarseregular
inatedbyaredpeak—seeFigure9below.Thesurfacedensity grid. Small-scale inhomogeneities in the Hi density are, how-
profile reflects the column density profile — the inner, dense ever, notlikelytohavemucheffectintheabsenceof dust.As
coreresultsinacentralpeakwhoserapiddeclinegiveswayto wehaveseentheLyαemissionprofilesmoothesthemover.At
ashallowerplateauaswereachtheouter,diffusebackground. most,anirregularedgeofanHiregionmayleadtoashallower
Figures7,8and9showacomparisonofthe2Dmapsand surfacebrightnessprofile.Inhomogeneitiesinthebulkvelocity
spectrafortheMDW(left)andWW(right)windprescriptions wouldhaveasomewhatgreatereffect,increasingthefrequency
forthethreehaloes.Notethattheleftpanel ofFigure8isthe diffusion.Theseinhomogeneitiescouldbemodelledasaturbu-
same as the left panel of Figure 3, and is reproduced in this lent velocity, which has a similarly small effect as raising the
Figurefor convenience. Asnotedabove, theemissionismore temperature.
extendedinthestrongerwindmodels,andstrongerwindspro- ThefactthatwehavesimplyinjectedLyαphotonsatthe
duceanarrowerspectraldistribution(notethedifferenceinthe centreof thehaloisaratherstrongalbeitobservationally mo-
horizontalscaleofthe2Dspectra). tivated assumption. Wolfe&Chen(2006)placed limitson the
spatialextentofinsitustarformationinDLAs,concludingthat
extended sources (radius & 3kpc, 0.4 arcsec) were very rare4.
As R08 and BH09 have argued, Lyα emission in the systems
5 DISCUSSION we are considering is most likely to be powered by star for-
mation, suggesting that their large observed sizes are the re-
Thedependence of the spectra, inboth theline shape and the
sult of radiative transfer through the surrounding neutral gas.
totalobservedsurfacebrightness,ontheviewingangleisvery
Ourmainfocusherehasbeenonwhethersuchascenarioisin-
strikingandisobviouslyveryimportantfortheinterpretationof
deedplausible.ThefactthattheHidensitypeaksverynearthe
observed(spatiallyextendedlowsurfacebrightness)Lyαemit-
centre of the halo means that the majority of photons should
ters.Itsuggests,e.g.,thatthelargevarietyoflineshapesinthe
be emitted near the centre of the halo, as we have assumed.
observed sample of R08 is at least partially an orientation ef-
Making the intrinsic Lyα emission more extended would ob-
fect. Thedependence of surface brightness on orientation fur-
viously make the observed emission also more extended. A
thersuggest that the“dutycycle”thatweintroducedinBH10
more realistic Lyα emissivity would need to consider the in-
mayalsobeinterpretedasanorientationeffect,withonlyacer-
teraction of UV radiation from star formation with the sur-
tainfractionofhaloesseenatanorientationwheretheobserved
rounding Hi, as well as the possible contribution from cool-
fluxexceedsthedetectionlimit.Aratherlargesampleofhaloes
ing radiation (Faucher-Gigue`reetal. 2010) and fluorescence
would be required to determine the probability distribution of
duetotheUVbackgroundandquasars(Cantalupoetal.2005;
theobservedLyαfluxfromahaloofgivenmassandintrinsic
Cantalupo,Porciani,&Lilly 2008). However, fluorescence is
luminosity. Asbrieflymentioned but not investigatedindetail
expected to contribute little to the Lyα emission from DLAs
here,thereshould,however,obviouslybealsoavariationofthe
(R08), and cooling is likely to only be significant in massive
spectral shapeand surface brightnessdistributionwithtimein
haloes,whicharen’texpectedtohostthebulkoftheDLApop-
particularwhenagalaxyundergoesamajormergerand/orstar-
ulation. While cooling radiation may not account for the bulk
burst.
of DLA lya luminosity, it could still be a relevant factor in
determining the observed size of the emitters, as the surface
brightness of the cooling radiation may drop less rapidly to-
5.1 Limitationsofthemodelling
wards large radii than the radiation scattered outwards from
We will discuss now again in more detail some of the limita- centralstar-formingregions(Dijkstra,Haiman,&Spaans2006;
tionsofourmodelling.Firstly,thefailureofthesimulationsof Dijkstra&Loeb2009;Faucher-Gigue`reetal.2010).
Tescarietal. (2009) to reproduce the high velocity tail of the
velocitywidthdistributionoftheassociatedmetalabsorptionin
DLAssuggeststhathigheroutflowvelocities,amoreextended 4 Some extended star-formation has recently been detected
spatialdistributionoftheneutralgas,and/oralessclumpyand (Rafelski,Wolfe,&Chen 2010) — as discussed previously, we
morespatiallyextendeddistributionoflow-ionisationmetalsis will investigate the effect ofspatially extended Lyαsources infuture
requiredfromourgalacticwindimplementations.Theeffectof work.
(cid:13)c 2010RAS,MNRAS000,1–17