Andromeda and its place in the local groupAlso need high angular resoluOon, to be able to map the...
Transcript of Andromeda and its place in the local groupAlso need high angular resoluOon, to be able to map the...
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