Deep wide field HI imaging of Messier 31

0.11 MB·English

by  Laurent Chemin

Deep wide field HI imaging of M31
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J LaurentChemin∗

5 GÉPI,ObservatoiredeParis,sectionMeudon,CNRS&UniversitéParis7UMR8111,5Place
1 JulesJanssen,92195Meudon,France

E-mail: [email protected]
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O
ClaudeCarignan
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. Laboratoired’AstrophysiqueExpérimentale(LAE),ObservatoiredumontMégantic,and
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Départementdephysique,UniversitédeMontréal,C.P.6128,Succ.Centre-Ville,Montréal,QC,
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Observatoired’Astrophysiquedel’UniversitédeOuagadougou(UFR/SEA),03BP7021
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t Ouagadougou03,BurkinaFaso
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[ TylerFoster

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DepartmentofPhysics&Astronomy,BrandonUniversity,Brandon,MB,CanadaR7A6A9
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2 Wereportonpreliminaryresultsfromanewdeep21-cmsurveyoftheAndromedagalaxy,based
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0 onobservationsperformedwiththeSynthesisTelescopeandthe26-mantennaatDRAO.TheHI
8. distributionandkinematicsofthediscareanalyzedandbasicdynamicalpropertiesarederived.
0 NewHIstructuresarediscovered,likethinHIspur-likestructuresandanexternalarminthedisc
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0 outskirts. TheHIspursarerelatedtoperturbedstellarclumpsoutsidethemaindiscofM31. The
: external arm lies on the far, receding side of the galaxy and has no obvious counterpartin the
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Xi oppositeside. TheseHIperturbationsprobablyresultfromtidalinteractionswithcompanions.It
r isfoundadynamicalmassof(4.7±0.5)×1011M⊙ enclosedwithinaradiusR=38kpcanda
a
totalmassof∼1×1012M⊙insidethevirialradius.
PanoramicRadioAstronomy: Wide-field1-2GHzresearchongalaxyevolution-PRA2009
June02-052009
Groningen,theNetherlands
∗Speaker.
(cid:13)c Copyrightownedbytheauthor(s)underthetermsoftheCreativeCommonsAttribution-NonCommercial-ShareAlikeLicence. http://pos.sissa.it/
DeepwidefieldHIimagingofM31 LaurentChemin
1. Introduction
Understanding theformationandevolution ofgalaxiesliketheMilkyWayisoneofthemajor
goal of astrophysics. The Andromeda galaxy (M31) is very well suited to put constrains on the
physicalprocessesthatcontroltheevolutionofspiralgalaxiesbecauseofitsproximity. Theimpor-
tantstellarfeatures relatedtotheevolution ofM31arethefaint,extended andperturbed structures
seen inthe disc outskirts, inaddition tomanyofthe dwarf companions that have been detected in
itscloseneighbourhood ([9]). Theyareundoubtedly theimprints ofthehierarchical growthofthe
stellar disc and halo of M31, similar tothose seen in numerical models of dark matter and galaxy
evolution intheframeworkoftheColdDarkMatterparadigm (e.g. [13]).
InthisworkweareinterestedinprovidingadetailedviewoftheneutralhydrogendiscofM31
from recent, deep, wide-field and high angular HI imaging. Our direct objectives are (i) to study
the most extended HI distribution of M31, (ii) to derive an accurate HI rotation curve for it, and
(iii)toderiveitsbasicdynamicalparametersinordertoputfurtherconstraints onthehistoryofits
mass assembly. A few preliminary results are described herefter. A complete analysis of the data
arepresented inCheminetal. (2009, [5]).
2. Observations
The HI observations were performed with the Synthesis Telescope and the 26-m dish at the
Dominion Radio Astrophysical Observatory (DRAO) between September and December 2005.
Fivefields were observed in the direction of M31for a total exposure time of144 hours per field.
Thespectral resolution is5.3kms−1 andtheangular sizeofthesynthesized beamis∼60”×90”.
Itsamplesalinearscaleof∼230pc×340pcattheM31distance (785kpc,[10]).
3. Results
TheintegratedemissionisdisplayedinFigure1(left-handpanel). ThehighresolutionHImap
showsadiscwithverylittlegasinitscentralregions,asususallyobservedinearly-typediscs. Faint
spiral-like or ring-like structures are observed at R∼2.5 kpc and R∼5 kpc. They coincide with
dusty ring-like structures observed inNIRimagesfromSPITZER-IRACdata ([1])aswellaswith
molecular gasring-like structures ([11]). Otherbrighter spiral-orring-like structures areobserved
between R∼ 9 kpc and R∼18 kpc. Part of these HI structures have already been presented in
previous studiesofM31([3,14]).
New faint structures that were not seen in old HI images are discovered. First the two disc
extremitiesexhibitthinspur-likeextensions, particularly towardstheNorth-East. Theirkinematics
are in good continuity to the adjacent inner disc. Velocity gradients are detected in these spurs
(∼20 km s−1 along ∼7−10 kpc). These spurs appear tightly linked to stellar clumps (the “G1"
clumpandtheNEextension, asidentifiedin[9]).
Then an external spiral arm is discovered on the edge of the receding half of the disc. It is
outlined with dashed lines in Figure 1 (right-hand panel). The HI mass of this new arm is ∼108
M⊙. Its apparent length is ∼ 32 kpc. It is connected to another more extended, brighter spiral
arm. Thearmisclumpytowardsitsnortheastern end. PartofthethinNEHIspursisakinematical
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DeepwidefieldHIimagingofM31 LaurentChemin
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Figure1: Left-handpanel: HI integratedemssionofMessier31. Right-handpanel: 3DviewoftheHI
datacube of M31. The top panel is the position-velocity diagram of the full datacube projected onto the
photometricmajoraxis. Thebottompanelisthesamemapasintheright-handpanelbutdisplayedwiththe
majoraxisparalleltothehorizontalaxis. Dashedlinesshowthelocationofthenewlydiscoveredexternal
arm(seetextfordetails).
extension of that external arm, as seen in the postion-velocity plot of Fig. 1. It is striking that the
external arm has no evident morphological and kinematical counterpart in the approaching half
of the disc with respect to the galactic centre. Moreover, it is obvious that its kinematics is very
peculiar compared to the disc velocities. As a consequence it is very likely that this spiral-like
structure hasbeengenerated byexternal effects toM31, either bytidal effects after thepassage of
agalaxysatelliteorevenbygasaccretionfromtheintergalactic mediumorfromaformergasrich
companion (NGC205?). Itisalsoremarkablehowthisexternalstructure hasasimilarmassasthe
Magellanic Stream in the halo of the Milky Way ([12]). Numerical simulations are necessary to
investigate thedifferent possibilities andfindtheorigin ofthefaint newperturbations. Notice that
weareconfidentabouttheirdetection becausetheyarealsoobservedintherecentHImapofM31
byBraunetal. (2009,[2]).
4. Dynamicalanalysis
Our previous dynamical analysis of M31 allowed us to derive a total mass of 3.4 ×1011 M⊙
for R < 35 kpc from single dish data obtained at Effelsberg and GBT ([4]). A new, more ex-
tended rotation curve is derived from a tilted-ring analysis of the velocity field of M31. A mass
distribution model is fitted to the rotation curve. As provisional results, it is derived a dynamical
mass of MDyn = (4.7±0.5)×1011 M⊙ inside R=38 kpc and a dark-to-baryonic mass ratio of
M /M ∼4.0 (79% of dark matter, 21% of luminous baryons). Here M represents
Dark Baryon Baryon
thesum oftheblack hole, gaseous and stellarmasses, M thedark mattermass. Thetotalmass
Dark
of M31 extrapolated to the virial radius (R∼160 kpc) is MVir ∼1.0×1012 M⊙. All these mea-
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DeepwidefieldHIimagingofM31 LaurentChemin
surementsareinexcellentagreementwithresultsfoundfromotherdynamicaltracers([7],[8])and
from another recent HI survey ([6]). A very good concensus seems to have been obtained for the
enclosed massinside theinner38kpcofM31,aswellasforitstotalmass. WerefertoCheminet
al. (2009, [5])foramoredetaileddiscussion oftheseresults.
Acknowledgements
We are very grateful to the staff of the Dominion Radio Astronomy Observatory at Pentic-
ton for their support in obtaining the observations, and especially T. Landecker for encouraging
us to pursue this project. We thank the scientific and local committees at ASTRON and Gronin-
gen for having organized the PRA 2009 conference and for all stimulating discussions during the
conference.
References
[1] BarmbyP.,AshbyM.L.N.,BianchiL.,EngelbrachtC.W.,GehrzR.D.,GordonK.D.,HinzJ.L.,
HuchraJ.P.,etal.2006,ApJ,650,L45
[2] BraunR.,ThilkerD.A.,WalterbosR.A.M.,&CorbelliE.2009,ApJ,695,937
[3] BrinksE.,&ShaneW.W.1984,A&ASS,55,179
[4] CarignanC.,CheminL.,HuchtmeierW.K.,&LockmanF.J.2006,ApJ,641,L109
[5] CheminL.,CarignanC.,FosterT.,2009,ApJ,705,1395
[6] CorbelliE.,etal.,2010,A&A,inpress,arXiv0912.4133
[7] EvansN.W.,WilkinsonM.I.,GuhathakurtaP.,GrebelE.K.,&VogtS.S.2000,ApJ,540,L9
[8] IbataR.,ChapmanS.,FergusonA.M.N.,IrwinM.,&LewisG.,2004,MNRAS,351,117
[9] IbataR.,MartinN.F.,IrwinM.,ChapmanS.,FergusonA.M.N.,LewisG.,&McConnachieA.W.
2007,ApJ,671,1591
[10] McConnachieA.W.,IrwinM.J.,FergusonR.A.,IbataR.A.,LewisG.F.,&TanvirN.2005,
MNRAS,356,979
[11] NietenC.,NeiningerN.,GuélinM.,UngerechtsH.,LucasR.,BerkhuijsenE.M.,BeckR.,&
WielebinskiR.,2006,A&A,453,459
[12] PutmanM.E.,etal.1998,Nature,394,752
[13] SpringelV.,WhiteS.D.M.,JenkinsA.,FrenkC.S.,YoshidaN.,GaoL.,NavarroJ.F.,ThackerR.,et
al.,2005,Nature,435,629
[14] UnwinS.C.1983,MNRAS,205,787
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