Intermediate-mass black holes in Globular Clusters

0.84 MB·English

by  Nora Lützgendorf

Mem.S.A.It.Vol.75,282
(cid:13)c SAIt 2008 Memoriedella
Intermediate-mass black holes in Globular
Clusters
N. Lu¨tzgendorf1,M.Kissler-Patig2,K.Gebhardt3,H.Baumgardt4,E.Noyola5,6,P.T.
3
1 deZeeuw1,7,N.Neumayer1,B.Jalali8,andA.Feldmeier1
0
2
1 EuropeanSouthernObservatory(ESO),Karl-Schwarzschild-Strasse2,85748Garching,
n
Germany
a
J e-mail:[email protected]
2 Gemini Observatory, NorthernOperations Center,670 N.A’ohokuPlaceHilo,Hawaii,
4
96720,USA
1
3 AstronomyDepartment,UniversityofTexasatAustin,Austin,TX78712,USA

4 School of Mathematics and Physics, University of Queensland, Brisbane, QLD 4072,
]
A Australia
5 InstitutodeAstronomia,UniversidadNacionalAutonomadeMexico(UNAM),A.P.70-
G
264,04510Mexico
. 6 UniversityObservatory,LudwigMaximiliansUniversity,81679Munich,Germany
h
7 SterrewachtLeiden,LeidenUniversity,Postbus9513,2300RALeiden,TheNetherlands
p
8 I.PhysikalischesInstitut,Universita¨tzuKo¨ln,Zu¨lpicherStr.77,50937Ko¨ln,Germany
-
o
r
t
s Abstract. ForasampleofnineGalacticglobularclusterswemeasuredtheinnerkinematic
a
profiles with integral-field spectroscopy that we combined with existing outer kinematic
[
measurements and HST luminosity profiles. With this information we are able to detect

1 thecrucialriseinthevelocity-dispersionprofilewhichindicatesthepresenceofacentral
v black hole. In addition, N-body simulations compared to our data will give us a deeper
8 insightinthepropertiesofclusterswithblackholesandstrongerselectioncriteriaforfurther
9 studies. Forthe first time, we obtain a homogeneous sample of globular cluster integral-
9 fieldspectroscopywhichallowsadirectcomparisonbetweenclusterswithandwithoutan
2 intermediate-massblackhole.
.
1
Keywords.Galaxy:globularclusters–blackholephysics–stars:kinematicsanddynam-
0
ics
3
1
:
v 1. Introduction X-ray and radio emissions, the central kine-
i
X matics in globular clusters can reveal possi-
ble IMBHs. However, resolving the gravita-
r Intermediate-massblackholes(IMBHs, M ∼
a • tionalsphereof influenceforplausible IMBH
102−105M )havedrawntheattentionofas-
⊙ masses (1′′ − 2′′ for large Galactic globular
tronomers for more than a decade and would
clusters)requiresvelocity-dispersionmeasure-
shedlightontothemysteryoftherapidgrowth
mentsatahighspatialresolution.Today,with
ofsupermassiveblackholesbyactingasseeds
the existence of the Hubble Space Telescope
intheearlystageofgalaxyformation.Besides
N.Lu¨tzgendorf:Intermediate-massblackholesinGlobularClusters 283
(HST) and high spatial resolution ground 2. Observations
based integral-field spectrographs, the search
forIMBHsispossible. Our sample consists of nine Galactic globu-
larclusters,eachofthemagoodcandidatefor
hosting an IMBHs at its center due its high
A strong motivation for searching for
massandcentralcuspinitslightprofile.
intermediate-massblackholesis the observed
relation between the black-hole mass and the These clusters were observed with the
velocity dispersion of its host galaxy (e.g. GIRAFFE spectrograph of the FLAMES
Ferrarese & Merritt 2000; Gebhardt et al. (Fiber Large Array Multi Element
2000a;Gu¨ltekinetal.2009).Exploringthisre- Spectrograph) instrument at the Very Large
lation in the lowermass range,wherewe find Telescope (VLT) using the ARGUS mode
intermediate-mass black holes, will give im- (Large Integral Field Unit). The velocity-
portant information about the origin and vali- dispersion profile was obtained by combining
dationofthiscorrelation. the spectra in radial bins centered around the
adoptedphotometriccenterandmeasuringthe
The formation of intermediate-massblack broadening of the lines using a non paramet-
holes can occurby the directcollapse of very ric line-of-sight-velocity-distribution fitting
massive first generation stars (Population III algorithm (for more detailed description see
stars,Madau&Rees2001),orrunawaymerg- Lu¨tzgendorf et al. 2011, 2012a; Lu¨tzgendorf
ingindenseyoungstarclusters(e.g.Portegies et al. 2012c, and Feldmeier et al. 2013, in
Zwart et al. 2004). This makes globular clus- prep.). For larger radii, the kinematic profiles
ters excellent environments for intermediate- were completed with radial velocity from
mass black holes. The currently best candi- the literature, if existent. In addition to the
dates for hosting an intermediate-mass black spectroscopicdata,HSTphotometrywasused
hole at their centers are the globular clusters to obtain the star catalogs, the photometric
ω Centauri (NGC 5139, Noyola et al. 2008, centeroftheclusteranditssurfacebrightness
2010;van derMarel & Anderson2010;Jalali profile. For each cluster both photometry
etal.2012),G1inM31(Gebhardtetal.2005), and spectroscopy were combined in order
and NGC 6388 (Lu¨tzgendorf et al. 2011). to apply analytic Jeans models to the data.
All of these very massive globular clusters The surface brightness profile was used to
show kinematic signatures of a central dark obtain a model velocity-dispersion profile
mass in their velocity-dispersion profiles. For whichwasfittothedatabyapplyingdifferent
ωCentauri,vanderMarel&Anderson(2010) black-hole masses and M/LV profiles. The
investigated a large dataset of HST proper final black-hole masses were obtained from a
motions and found less evidence for a cen- χ2fittothekinematicdata.
tral IMBH than proposed by Noyola et al.
(2008). Using a new kinematic center, how-
ever, Noyola et al. (2010) and Jalali et al.
3. N-bodysimulations
(2012)confirmedthesignatureofadarkmass
in the center of ω Centauri and proposed a Furthermore, we run N-body simulations
∼40000M⊙IMBH. basedontheGPU(GraphicProcessingUnit)-
enabledversionofthecollisionalN-bodycode
Further evidence for the existence of NBODY6 (Aarseth 1999).The code treats bi-
IMBHs is the discovery of ultra luminous X- nary interactions, stellar evolution, and exter-
ray sources at non-nuclear locations in star- nal tidal fields in a highly sophisticated man-
burst galaxies (e.g. Matsumoto et al. 2001; nerwhichallowsdetailedsimulationsofglob-
Fabbiano et al. 2001). The brightest of these ular clusters with and without central IMBHs
compactobjects(withL ∼ 1041 ergs−1)imply andtheirobservableeffects.Thegoalsofthese
masses largerthan 103M assumingaccretion simulationscanbesummarizedinthreemajor
⊙
attheEddingtonlimit. points:
284 N.Lu¨tzgendorf:Intermediate-massblackholesinGlobularClusters
Fig.1. VelocitymapsofthenineGalacticglobularclustersofoursample.
1)ReproduceObservations:Ourobserved ordertotestouranalyzingmethodsinphotom-
clusters will be compared to a grid of scaled etry and spectroscopy. This will give new in-
N-bodysimulationsinordertofindthebestfit- sightsonhowreliablethemethodofintegrated
tinginitialparametersandconstraintheblack- lightisintermsofrecoveringtheinnerdynam-
hole mass, M/L profilesand massfunctions. ics of dense stellar systems. 3) Study cluster
V
In contrast to Jeans models, N-body simula- properties: We are analyzing cluster simula-
tionscanconsiderthe effectof brightstars on tions with different black-hole retention frac-
the velocity measurements as well as strong tions, IMBH masses and binary fractions in
masssegregationofstellarremnantsinthecen- tidalfields.Withthesemodelswewillbeable
ter. 2) Test our Analysis: With the output of to put constraints on our preliminary black-
the N-body simulationswe are creating mock holemasses,verifythemeasurementsandpre-
datasets ofHST imagesandIFU datacubesin dictnewobservablesforfindingIMBHs.
N.Lu¨tzgendorf:Intermediate-massblackholesinGlobularClusters 285
lationsincludestellarevolution,binaryforma-
tionandanexternaltidalfieldwhiletheIMBH
1010 GGalolabxuileasr Clusters mass,theblack-holeretentionfractionandthe
McConnell et al. 2011
Bestfit GCs primordialbinaryfractionarevaried.Withthe
outcome of these simulations we will be able
108 to reproduce our observations, test our analy-
sismethods,andgetadeeperunderstandingof
)N
MSU theobservableeffectsofIMBHstotheirenvi-
(H 106 ronment(Lu¨tzgendorfetal.2013b,inprep.).
MB
NGC5139
NGC6388 G1 References
104
NGC1904
NGC5286 NGC6266 Aarseth,S.J.1999,PASP,111,1333
Fabbiano,G.,Zezas,A.,&Murray,S.S.2001,
102 ApJ,554,1035
10 100
σ (km/s) Ferrarese,L.&Merritt,D.2000,ApJ,539,L9
Gebhardt,K.,Rich, R. M., &Ho, L.C. 2005,
Fig.2. M −σ relations of IMBHs and SMBHs ApJ,634,1093
•
in comparison. Theslope of the bestfit to the GCs Gebhardt, K., Pryor, C., O’Connell, R. D.,
(green line) is by a factor of two smaller than the Williams, T. B., & Hesser, J. E. 2000a,AJ,
slopeoftheSMBHsingalaxies(blueline). 119,1268
Jalali, B., Baumgardt, H., Kissler-Patig, M.,
etal.2012,A&A,538,A19
4. ResultsandConclusions
Gu¨ltekin, K., Richstone, D. O., Gebhardt, K.,
We have investigated the presence of IMBHs etal.2009,ApJ,698,198
in nine Galactic globular clusters using a Lu¨tzgendorf,N.,Kissler-Patig,M.,Noyola,E.,
combinationofHST photometryandintegral- etal.2011,A&A,533,A36+
field spectroscopy. Comparing the velocity- Lu¨tzgendorf, N., Kissler-Patig, M., Gebhardt,
dispersion profiles in the central region of K.,etal.2012a,A&A,542,A129
eachGCswithanalyticalJeansmodelsyielded Lu¨tzgendorf, N., Kissler-Patig, M., Gebhardt,
four candidates which show an IMBH signa- K.,etal.2012c,arXiv:1212.3475
tureintheirkinematics(seeLu¨tzgendorfetal. Madau,P.&Rees,M.J.2001,ApJ,551,L27
2011, 2012a; Lu¨tzgendorf et al. 2012c, and vanderMarel,R.P.&Anderson,J.2010,ApJ,
Feldmeieretal. 2013,in prep.).Using ourre- 710,1063
sultsandIMBHmeasurementsfromthelitera- Matsumoto, H., Tsuru, T. G., Koyama, K.,
ture,westudythe M −σrelationforIMBHs etal.2001,ApJ,547,L25
•
andcompareittosupermassiveblackholesin McConnell, N. J., Ma, C.-P., Gebhardt, K.,
galaxies. Figure 2 (Lu¨tzgendorf et al. 2013a, etal.2011,Nature,480,215
in prep.) shows this comparisonand indicates Noyola, E., Gebhardt, K., & Bergmann, M.
a lower slope for the correlation at the lower 2008,ApJ,676,1008
mass end compared to the slope obtained for Noyola, E., Gebhardt, K., Kissler-Patig, M.,
the SMBHs by McConnell et al. (2011). The etal.2010,ApJ,719,L60
reasonforthisbehaviorcouldbeexplainedby Portegies Zwart, S. F., Baumgardt, H., Hut,
high mass loss of the globularclusters due to P.,Makino,J., &McMillan,S. L.W. 2004,
tidal stripping. This could lower the velocity Nature,428,724
dispersionofthesystemandmovestheglobu-
larclustersawayfromthe M −σrelation.
•
In addition to the observational work we
performedN-bodysimulationsin orderto ad-
dressopenquestionanddegeneracy.Thesimu-