Review:EmpiricalResultsonAttenuationCurves

NaveenReddyDustingtheUniverse,Tucson,AZ,07March2019

OutlineoftheReview• Whatisthestellarattenuationcurve?

• Whyisitimportant?

• Whatdoesitdependon?

• Whataboutthenebularattenuationcurve?

• A“roadmap”ofdustcurvesathigh-redshift

Definitions…

• NotethatE(B-V)dependsontheshapeofthedustcurve,k

• “Extinction”vs.“Attenuation”

**Formostofthistalk,Iwillbefocusingonthestellarattenuationcurve

ImportanceoftheDust“Curve”

Calzetti(2011)

ImportantinputtoSEDfitting

Neededtoinferdust-correctedSFRs

Encodesinfoonthedust/starsgeometry

DynamicRangeLimitsUsefulnessofFar-IRDataforsub-L*galaxiesathigh-z• Typical(L*)galaxiesatz>2arelargelyundetectedatfar-IRwavelengths(requirestacking)

• ALMAisuseful…but,stillrequiresafewhoursperobjectanduncertaincalibrationstocomputetotalSFRs

Reddy+12a

ImportanceofQuantifyingtheWavelength-DependenceofDust

Obscuration• InferringthePhysicalPropertiesoftheISMbasedonrest-frameopticallineratios(e.g.,ionizationparameters,gas-phasemetallicities,nebularreddeningandrecombination-lineSFRs)

• InvestigationsoftheoriginofthecarriersofspecificabsorptionfeaturesintheUV

Buat+11

ImportanceoftheDust“Curve”forModelingStellarPopulations

Reddy+16b

InvestigatingtheCurve…typicallyaccomplishedusingtheIRX-betarelation

Meurer+99

Dustiness

RedderUVslope

Meurer+99

“Steeper”

Whatdoesthecurvedependon?• MusttakeintoaccountStar-formationhistory/Age/sSFR

Kong+04

Buat+12

Reddy+10

**Importanttodisentanglevariationsinstellarpopulationsfromchangesintheshapeofthedustcurve

Whatdoesthecurvedependon?• GEOMETRY

Battisti+17 Wang+18

Wild+11

e.g.,seealsoNarayanan+18

Geometricaleffectsmayplayaroleinthe“strength”ofthe2175bump

Whatdoesthecurvedependon?• Luminosity(ortotalSFR)

Reddy+06Casey+14

z~2

Whatdoesthecurvedependon?• Luminosity(ortotalSFR)

Reddy+06Casey+14

z~2

Reddy+10

z~2galaxiessignificantlymoreluminousatafixedIRX(e.g.,seealsoWhitaker+17)

Whatdoesthecurvedependon?• (Stellar)Metallicity(alsorelatedtoSFH,sSFR,mass,etc.)

Reddy+18a

e.g.,seealsoWilkins+11,Boquien+12,Schaerer+13,deBarros+14,Zeimann+15

Whatdoesthecurvedependon?• (Stellar)Metallicity(alsorelatedtoSFH,sSFR,mass,etc.)

SMCappliesbestforhigh-zsub-solarmetallicitystellarpopulationswithblueintrinsicUVslopes

Reddy+18a

GoingbeyondIRX-Beta

Kriek&Conroy(2013)

Slopeofattenuationcurve/strengthofUVbumpinverselycorrelatewithspecificSFR(basedonstackedphotometryofz~1.5galaxies)

• Constraintsontheoverallshape/normalizationofthestellarattenuationcurve(e.g.,Noll+09,Kriek&Conroy13,Scoville+15,Reddy+15,Zeimann+15))

CurveintermediatebetweenthatofCalzettiandSMCforz~2galaxies

Reddy+15

TheFar-UVShapeoftheDustCurve• NewconstraintsontheshapeofthedustcurveclosetotheLymanBreak

Maybeusedtoassessattenuationofionizingphotonsinlow-columndensityISM(<10^17.2cm^-2)orinHIIregions

• Mostdustcurves,includingthatofCalzetti,haveonlybeenconstrainedabove1250Angstroms

• Newdeterminationforz~3LBGssuggestsashallower(lesssteep)wavelengthdependencebetween950and1250A

Reddy+16a

Whataboutthenebularattenuationcurve?

• Curvethatappliesfordustreddeningalongthelines-of-sighttotheionizedISM(i.e.,towardsmassivestars)

• Requiredtointerpretrest-frameopticallineratiostocomputeISMphysicalproperties

• Apriorithereisnoreasonwhythecurveshouldbethesameasthataffectingthestellarcontinuum(cov.fractionofdust/geometry)northesameastheMWextinctioncurve

canbeinvestigatedusingmultiplerecombinationlineratios

MOSFIREDeepEvolutionField(MOSDEF)Survey

•  Rest-frame optical spectra of ∼ 1800 H-selected galaxies and AGNs

•  1.37 ≤ z ≤ 3.80 •  CANDELS fields •  48.5 nights with MOSFIRE on Keck I (2012-2016) •  Collaboration between UC Berkeley, UCLA, UC San

Diego, UC Riverside

Surveypaper:Kriek+2015

J(1.2μm) H(1.6μm) K(2.2μm)

MultipleBalmeremissionlinesfromCompositeSpectraatz~2

Reddyetal.,inprep

ShapeofNebularAttenuationCurveatz~2

Calzetti/SMC

z~2

CURVEATz~2HASMORECURVATUREINTHEREST-OPTICAL,SIMILARTOCCMCurve

Reddyetal.,inprep

ShapeofNebularAttenuationCurveatz~2

• Suggestssomedegreeofdustsegregationevenfortypicalstar-forminggalaxiesathighredshift

• MayindicatesignificantscatteringofUVlightfromregionsofmassivestarformation(e.g.,Calzetti+94,Ma+19)

• and/orhigherdustcoveringfractionstowardsmassivestars

• Intrinsiccurvemaybethesamethroughoutthegalaxy,butgeometrymaydictateobservedshapeofattenuationcurve

A“Roadmap”fortheAttenuationCurveatHighRedshift

IncreasingSFR/Stellarmass

GrayerthanCalzetti?

Limitedusegivendust

opticaldeptheffects

DSFGs

Appearstobesteep(e.g.,SMC-

like)

AccountforredintrinsicUVslope,thuscouldbe

consistentwitha“starburst”-likecurve;inclinationeffectsprobablyimportant

Massive/lowsSFR

SimilartoCalzettioracurvethatisslightlysteeper

IntrinsicslopestillbluerthanthatusedtocalibrateMeurer

relation;inclinationeffectsprobably

importantformoremassivegalaxies

UV-bright(>L*)

AppeartobeuniformlysteeperthanCalzetti(SMC-

like?)

VeryblueintrinsicUVslopenecessitatesuse

ofsteepcurvetoreproduceIRX-betarelation;geometry

probablylessimportant

UV-faint(<L*)