Andromedaanditsplaceinthelocalgroup

YlvaPihlström,UNM

M31-TheAndromedaGalaxy

•  Atadistanceof2.5millionlightyears,ourclosestlargeneighbor

•  Canseewithnakedeye

•  Spiralgalaxy

•  Mass1.2x1012M⊙M32

M110

N

Messier&Hubblemadeitknown

From Messier’s work in 1700’s.

•  Messiercataloguedit

•  Hubblein1920’susedCepheidvariablesinAndromedatodeterminedistance–  “Islanduniverse”

•  Significantlychangedtheviewoftheuniverseasweknewit

MulO-wavelengthview

X-ray

MulO-wavelengthview

UV

MulO-wavelengthview

Optical

MulO-wavelengthview

Infrared

MulO-wavelengthview

Radio

MulO-wavelengthview

Gascomponents

Atomic Hydrogen CO gas

StructuresintheUniverse

•  Hierarchyofstructures:–  Galaxy

–  Group/cluster

–  Supercluster

•  Agrouporclusterofgalaxiescontain10-1000sofmembers

•  M31andMilkyWaybelongtotheLocalGroup–  About50members

The Antennae

NumericalsimulaDons–whatgravitydoes

Walker et al. 1996

StandardevoluDonarymergerscenario

•  TheToomresequence(fromsimulaOons),belowinimages.Asequenceofobservedgalaxiesthatarethoughttobeindifferentstagesofmajormergerbetweentwospirals.

•  MergerrateasafuncOonoflook-backOmeinformusabouthowstructuresformandevolve

Mergers

•  AffectthestarformaOonrate–  Minorversusmajormergers–  Smallonescontributesignificantly

(Kavirajetal.2016)

•  Metallicity

•  Shapeofcentralbulges

•  Growthofcentralblackholes

=>Extremelyimportantforgalaxyevolu3onscenarios

NGC7714

EvoluDonwithintheLocalGroup

WhatistheevoluOonaryscenariofortheLocalGroup?

•  DominatedbyM31andtheMilkyWay(MW),movingtowardeachotherwithapproximately120km/s

•  AssumingtheLocalGroupisgravitaOonallybound=>mergerbetweentheMWandM31

Cox & Loeb 2008

DistancebetweenMWandM31asafuncOonofOme

Cox & Loeb 2008

DistancebetweenMWandM31asafuncOonofOme,mulOplemodels

Cox & Loeb 2008

> 3.5 Gyr

2 Gyr

NASA; ESA; A. Feild and R. van der Marel, STScI

•  ThemodeledhistoryandevoluOonoftheM31-MWsystemneedsconstraints

•  DependsstronglyonthetransversevelocityofM31–  OnlyhaveradialvelociOes,need3D

vy =120 km/s

MW

M31

y

x

•  ThemodeledhistoryandevoluOonoftheM31-MWsystemneedsconstraints

•  DependsstronglyonthetransversevelocityofM31–  OnlyhaveradialvelociOes,need3D

MW

M31

v = f(vx, vy) = ?

y

x

vy =120 km/s

vx = ?

Wecanmeasuretheradialvelocity,vy,viaDopplershid.

•  Forfullvelocityvectorweneedthetransversevelocity,vx

•  Getfromthepropermo3onintheplaneofthesky:theapparentangularmoOonofanobjectacrossthesky

TimebetweenobservaOonsknown,andthedistance=>transversevelocity

t t + dt

x

𝛼d

vx

However,verysmallangularchangesandM31ishuge!

Plan:tofindsomethingmuchsmaller,verycompact,withinthegalaxyandfollowthatobjectwithhighangularresoluOonobservaOons.

Expect motion of 15-50𝜇as/yr, only a small fraction of the galaxy extent.📍

Itmustbecompact,bright,andpreferablynon-variable.

ConOnuumsourcesinM31:

•  M31*:acompactradiosourceinthecenterofthegalaxy,thedynamicalcenter

•  X-RayBinaries

Willnotwork:InM31theseonesaretooweak.

📍Whatcanweuseasapin?Intensity

Wavelength

X-ray binary, artist’s impression

AnotheropOonislineemission,frommolecules.

We’remainlyinterestedinmasers:

BrightamplifiedemissionfromexcitedmoleculartransiOons

Ex:H2Oat22GHz,OHat1.6GHz,CH3OHat6.7and12GHz,SiOat43GHz

Intensity

Wavelength

•  MicrowaveAmplificaOonbySOmulatedEmissionofRadiaOon

absorption spontaneous emission

n1< n2

amplification

E

E

n1

n2

n2

n1

AlsoneedhighangularresoluOon,tobeabletomapthemaser‘spots’asafuncOonofOme.

•  VeryLongBaselineInterferometry

(VLBI)measuresposiOonswithafew10𝜇asaccuracy.

Examples:theVeryLongBaselineArray(VLBA),theEuropeanVLBINetwork

ResoluOondependsontelescopedistance–thefurtherapart,thehigherangularresoluOon.

M33&IC10H2OmaserssuccessfullyobservedinM33andIC10,givingpropermoOons(Brunthaleretal.2005,2007)

Brunthaler et al. 2007

Task:FindmaseremissioninM31

H2Oisaprimechoice:

•  ProvideshighposiOonalaccuracy

•  FoundinregionsofstarformaOon,frequentlyobservedinMWandalsoinM33andIC10

SizeofM31isaproblem,asthefield-of-viewissmallforthewavelengthsofinterest

•  TakesverylongOmetodoablindsearchofM31

•  TargetedsearchesforH2Oat22GHzchallenging

–  Mainbeamissmall:Hardtocoverfullextentofgalaxy

•  1.6GHzOH–  LargermainbeambutworseposiOonalaccuracy=>toolongOmebaseline!

–  Also,noOHmasersinM31…

•  Methanolat6.7/12.2GHz

–  Intermediatesizedbeam

Darling et al. 2016

Methanolat6.7GHz

•  WithVLAupgradein2009,webeganablindsurveysearchingfor6.7GHzmethanolmasers

N

•  Severalweakmasersdetected,sofarmostinthemid-galaxy

Dec

linat

ion

(J20

00)

Right Ascension (J2000)00 45 44 43 42 41

42 00

41 50

40

30

20

10

00

40 50

40

X

Y

Flux

(mJy

/bea

m)

Heliocentric velocity (km/s)

-340 -320 -300 -280 -260 -240

12

10

8

6

4

2

0

-2

-4

Flux

(mJy

/bea

m)

Heliocentric velocity (km/s)

-270 -260 -250 -240 -230 -220 -210

8

7

6

5

4

3

2

1

0

-1

-2

September 2009

VLAfollow-up

•  Widthabout5km/s,peakabout8mJy/beam.

•  High-endtailofthe6.7GHzmethanolmaserdistribuOonintheMilkyWay–  W3(OH)3700Jy=>M31maserat

samedistance1300Jy

•  Noassociated22GHzwatermaser

•  Notclose(<50pc)ofastarformingregion,H-alphaemissionlineregionoracompactHIIregion.

Sjouwerman et al. 2010

July 2010

Methanolmaserisapossiblepin

•  VLAtelescopesaretooclosetogetsufficientposiOonaccuracy

•  GlobalobservaOonsincluding44telescopesacrosstheworld

–  4x6hrs

•  Currentlyworkingonthisdata

–  Maybetoo‘diffuse’,spreadoversizescalesthetelescopearrangementisnotsensiOvetoo

Atthispoint,wesOlldonotknowthetransversevelocityofM31,butthereareseveralgroupsworkingonit.

Whatmayhappentothesolarsystem?

Oncewehavethetransversevelocity,wewillbeabletobeverconstraintheLocalGroupfuture.

Meanwhile,speculate:Whathappenstothesolarsystem?

ExcludinginteracOon:Sunwilldevelopintoredgiant:

WithinteracOon:TaggingparOcles

Summaryremarks:

TheAndromeda–MilkyWaysystemisofgreatinterest:Cluestothepast,andtotheevoluOonofourLocalGroup

NASA, ESA, Z. Levay and R. van der Marel (STScI), T. Hallas, and A. Mellinger