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“Local Universe” (within ~ 20 Mpc) Distance Indicators if we know the absolute magnitude of an object (M) and can measure its apparent magnitude (m), we can derive the distance from (where remember the distance must be expressed in parsecs!) Propagation of errors show how the uncertainty in distance relates to the uncertainty in distance modulus: Local Universe Standard (or Standardizable) Candles: Pulsating Variables: Cepheids or RR Lyrae stars (already talked about) Tip of the Red Giant Branch (TRGB) Surface Brightness Fluctuations (SBF) Planetary Nebulae Luminosity Function (PNLF) Globular Cluster Luminosity Function (GCLF) m - M = 5 log d - 5 σ d d 0.5 σ (m-M )

m M = 5log d 5burro.astr.cwru.edu/Academics/Astr328/Notes/LocalUniverseDistances.pdf · The hot C/O core (young white dwarf) ionizes these expanding shells, causing them to fluoresce

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Page 1: m M = 5log d 5burro.astr.cwru.edu/Academics/Astr328/Notes/LocalUniverseDistances.pdf · The hot C/O core (young white dwarf) ionizes these expanding shells, causing them to fluoresce

“LocalUniverse”(within~20Mpc)DistanceIndicators

ifweknowtheabsolutemagnitudeofanobject(M)andcanmeasureitsapparentmagnitude(m),wecanderivethedistancefrom

(whererememberthedistancemustbeexpressedinparsecs!)

Propagationoferrorsshowhowtheuncertaintyindistancerelatestotheuncertaintyindistancemodulus:

LocalUniverseStandard(orStandardizable)Candles:

• PulsatingVariables:Cepheids orRRLyrae stars(alreadytalkedabout)• TipoftheRedGiantBranch(TRGB)• SurfaceBrightnessFluctuations(SBF)• PlanetaryNebulaeLuminosityFunction(PNLF)• GlobularClusterLuminosityFunction(GCLF)

m�M = 5 log d� 5

�d

d⇡ 0.5⇥ �(m�M)

Page 2: m M = 5log d 5burro.astr.cwru.edu/Academics/Astr328/Notes/LocalUniverseDistances.pdf · The hot C/O core (young white dwarf) ionizes these expanding shells, causing them to fluoresce

TipoftheRedGiantBranch

ConsidertheevolutionofstarsliketheSun.

Aftertheyexhausthydrogeninthecore,theyevolveoffthemainsequence.

Theheliumcorecontractsandheatsup;hydrogenburninghappensinashellaroundthecoreatafuriouspace.Thestarbecomesluminousandswellsup,becomingaredgiant.

Whenthecorecontractsandheatsenoughtobeginfusingheliumintocarbonandoxygen,thatenergyreleaseexpandsthecore,reducingthenuclearreactionratesandcausingthestartoevolveofftheRGBandontothehorizontalbranch.

TheRGB“Tip”isthebrightestluminosityaRGBstarcanattaininitsevolution.Ifagalaxyiscloseenoughforustoseeindividualstars,wecanuseTRGBtogetadistance.

Page 3: m M = 5log d 5burro.astr.cwru.edu/Academics/Astr328/Notes/LocalUniverseDistances.pdf · The hot C/O core (young white dwarf) ionizes these expanding shells, causing them to fluoresce

M15:Metalpoor

47Tuc:Metalrich

RedGiantBranchMetallicity Effects

Page 4: m M = 5log d 5burro.astr.cwru.edu/Academics/Astr328/Notes/LocalUniverseDistances.pdf · The hot C/O core (young white dwarf) ionizes these expanding shells, causing them to fluoresce

fromMadore+18

>

fromBeaton+18

CalibratingtheTip

WeneedtoknowtheabsolutemagnitudeoftheTRGB.Butthisismetallicity-dependent:metal-richRGBstarsareredder,andsotheirfluxmovesintoredderfilters.

Asafunctionofmetallicity,theRGBtipbecomesfainterinopticalfilters,brighterininfraredfilters.

WecancalibratetheRGBtipusingstellarevolutionmodels.Worksbestforoldpopulations.

Page 5: m M = 5log d 5burro.astr.cwru.edu/Academics/Astr328/Notes/LocalUniverseDistances.pdf · The hot C/O core (young white dwarf) ionizes these expanding shells, causing them to fluoresce

fromBeaton+18

MeasuringtheTipNGC185

MeasureRGBcolorandtipmagnitude• RGBcoloràMtip =−4.06± 0.12• mtip =20.43± 0.03

m−M=20.43−−4.06=24.49thencorrectfor0.28magofextinctiontoget:

m−M=24.21± 0.03(ran)± 0.12(sys)

ord=0.7± 0.08Mpc

Currentdistancelimit~Virgo(16.5Mpc)

Page 6: m M = 5log d 5burro.astr.cwru.edu/Academics/Astr328/Notes/LocalUniverseDistances.pdf · The hot C/O core (young white dwarf) ionizes these expanding shells, causing them to fluoresce

SurfaceBrightnessFluctuations

Thinkofaglobularclusterversusanellipticalgalaxy.Whichlooks“grainier”?

Page 7: m M = 5log d 5burro.astr.cwru.edu/Academics/Astr328/Notes/LocalUniverseDistances.pdf · The hot C/O core (young white dwarf) ionizes these expanding shells, causing them to fluoresce

SBFmethod

Thinkoftakinganimageoftwogalaxiesatdifferentdistances.

Numberofstarsperpixel:

Fluxfromtheindividualstars:

Sothesurfacebrightnessdoesn’tchange:

Butinagivenimage,therandomscatterinpixelintensitiesgoesas

Soconsiderthepixelvariancedividedbyaveragesurfacebrightness:

wheref* canberelatedto(butisnotthesameas!)theaveragefluxperstar.Expressedinmagnitudes,thisis referredtoasthefluctuationmagnitude.

N⇤pix

⇠ d2

f⇤ ⇠ d�2

SB ⇠ N⇤ ⇥ f⇤ = constant

�I ⇠p

N⇤ ⇥ f⇤ ⇠ d�1

NearbygalaxyDistantgalaxy

�2I

SB⇠ N⇤f2

⇤N⇤f⇤

⇠ f⇤

Page 8: m M = 5log d 5burro.astr.cwru.edu/Academics/Astr328/Notes/LocalUniverseDistances.pdf · The hot C/O core (young white dwarf) ionizes these expanding shells, causing them to fluoresce

Jensen+03

Samemetallicity effectthatwesawusingTRGBstars.

Page 9: m M = 5log d 5burro.astr.cwru.edu/Academics/Astr328/Notes/LocalUniverseDistances.pdf · The hot C/O core (young white dwarf) ionizes these expanding shells, causing them to fluoresce

Whatkindofgalaxywouldthisworkwellfor?Whatkindwouldn’titworkwellfor?

Page 10: m M = 5log d 5burro.astr.cwru.edu/Academics/Astr328/Notes/LocalUniverseDistances.pdf · The hot C/O core (young white dwarf) ionizes these expanding shells, causing them to fluoresce

SBFdistanceapplication:thestructureoftheVirgoCluster

(mapcourtesySpengler+18)

Page 11: m M = 5log d 5burro.astr.cwru.edu/Academics/Astr328/Notes/LocalUniverseDistances.pdf · The hot C/O core (young white dwarf) ionizes these expanding shells, causing them to fluoresce

Virgocluster“tomography”:

Virgoellipticalgalaxiesatdifferentdistances(Mei+07)

Page 12: m M = 5log d 5burro.astr.cwru.edu/Academics/Astr328/Notes/LocalUniverseDistances.pdf · The hot C/O core (young white dwarf) ionizes these expanding shells, causing them to fluoresce

Virgovelocityfield:

distortionoftheHubbleFlow(Mei+07)

Page 13: m M = 5log d 5burro.astr.cwru.edu/Academics/Astr328/Notes/LocalUniverseDistances.pdf · The hot C/O core (young white dwarf) ionizes these expanding shells, causing them to fluoresce

PlanetaryNebulaLuminosityFunction

Stellarevolutionrecap:

Attheendoftheirlives,aftertheyrunoutofHeintheircore,solartypestarsejectouterlayers.

ThehotC/Ocore(youngwhitedwarf)ionizestheseexpandingshells,causingthemtofluoresce.

Weseetheminopticalemissionlines(mostnotably[OIII]5007A).

Beautifulinourgalaxy,butsmall(parsecscale).Inothergalaxiestheyaresimplyunresolvedemissionlinesources.

Page 14: m M = 5log d 5burro.astr.cwru.edu/Academics/Astr328/Notes/LocalUniverseDistances.pdf · The hot C/O core (young white dwarf) ionizes these expanding shells, causing them to fluoresce

Pne inM101(Feldmeier+09)

[OIII]:emissionline5300:continuum(regularstarlight)

Page 15: m M = 5log d 5burro.astr.cwru.edu/Academics/Astr328/Notes/LocalUniverseDistances.pdf · The hot C/O core (young white dwarf) ionizes these expanding shells, causing them to fluoresce

PlanetaryNebulaLuminosityFunction

PNLF:NumberofPNe asafunctionofemissionlineluminosity.

ThePNLFshowsasharpcutoffatbrightmagnitudes,relatedtothemaximumsizeoftheionizingWD.

M*=−4.53± 0.06(Ciardullo+12)

N(m) ⇠ e0.307M (1� e3(M⇤�M))

Page 16: m M = 5log d 5burro.astr.cwru.edu/Academics/Astr328/Notes/LocalUniverseDistances.pdf · The hot C/O core (young white dwarf) ionizes these expanding shells, causing them to fluoresce

GlobularClusterLuminosityFunction

GC(M80)intheMilkyWay

GCsintheVirgoCluster(littledots)

Page 17: m M = 5log d 5burro.astr.cwru.edu/Academics/Astr328/Notes/LocalUniverseDistances.pdf · The hot C/O core (young white dwarf) ionizes these expanding shells, causing them to fluoresce

GlobularClusterLuminosityFunction

GCLFtypicallymodeledasaGaussian.Ifthemagnitudeofthepeak(note:notthesameasthepeakmagnitude!)isconstantacrossgalaxies,thiscanbeusedasadistanceindicator.

Page 18: m M = 5log d 5burro.astr.cwru.edu/Academics/Astr328/Notes/LocalUniverseDistances.pdf · The hot C/O core (young white dwarf) ionizes these expanding shells, causing them to fluoresce

Woodley+10

WhileGCscanbebright,youneedtoseethefaintonestoestimatethepeak!

Observationalincompletenessatfaintmagnitudesisarealcomplication.

Page 19: m M = 5log d 5burro.astr.cwru.edu/Academics/Astr328/Notes/LocalUniverseDistances.pdf · The hot C/O core (young white dwarf) ionizes these expanding shells, causing them to fluoresce

Comparisonoflocaldistanceindicators

M101,theSombreroGalaxy(McQuinn+16)