The Globular Cluster System The Globular Cluster System of NGC 5128: Ages, Metallicities, of NGC 5128: Ages, Metallicities,

Kinematics and Structural Kinematics and Structural ParametersParameters

Kristin A. WoodleyKristin A. Woodley

McMaster University, CanadaMcMaster University, Canada

William HarrisWilliam Harris McMaster UniversityMcMaster University

Matías GómezMatías Gómez Universidad Andres Bello Universidad Andres Bello

Thomas PuziaThomas Puzia Herzberg Institute of AstrophysicsHerzberg Institute of Astrophysics

Gretchen HarrisGretchen Harris University of WaterlooUniversity of Waterloo

Doug GeislerDoug Geisler Universidad de ConcepciónUniversidad de Concepción

OutlineOutline Globular Clusters (GCs)Globular Clusters (GCs)

GC system – constraining the formation of NGC GC system – constraining the formation of NGC 51285128

Ages, metallicities, and formation timescales of GCs Ages, metallicities, and formation timescales of GCs

Kinematics of the red and blue GCsKinematics of the red and blue GCs

GCs as tracers of mass GCs as tracers of mass

Structural Parameters of the red and blue GCsStructural Parameters of the red and blue GCs

SummarySummary

Globular Clusters (GCs)Globular Clusters (GCs)

GCs are tracers of star GCs are tracers of star formation episodes in their formation episodes in their host galaxyhost galaxy Formation of massive star Formation of massive star

clusters in interacting and clusters in interacting and starbursting galaxies starbursting galaxies (Whitmore & Schweizer 1995)

Advantages:Advantages: Coeval structuresCoeval structures Large GC systems in early-Large GC systems in early-

type galaxiestype galaxies Multi-object spectrographs – Multi-object spectrographs –

ages, chemical compositions, ages, chemical compositions, radial velocity measurementsradial velocity measurements

Estimated ~1500-2500 GCs Estimated ~1500-2500 GCs

(Harris et al. 2006)(Harris et al. 2006) N = 605 GCs N = 605 GCs

268 are metal-poor268 are metal-poor 271 are metal-rich271 are metal-rich

R < 45 arcminR < 45 arcmin

Radial Velocity Studies:Radial Velocity Studies:1. van den Bergh et al. (1981)2. Hesser et al. (1984)3. Hesser et al. (1986)4. Harris et al. (1992)5. Peng et al. (2004)6. Woodley et al. (2005)7. Rejkuba et al. (2007)8. Beasley et al. (2008)9. Woodley et al. (2009a) 10. Woodley et al. (2009b)Resolved GC Study:Resolved GC Study:1. Harris et al. (2006)

The GC System of NGC 5128The GC System of NGC 5128

MPMRNo photometry

Ages and Metallicities of GCsAges and Metallicities of GCsAge and metallicity distribution functions can provide information of Age and metallicity distribution functions can provide information of

when GCs of different metallicity formwhen GCs of different metallicity form

Integrated light of GCsIntegrated light of GCs Gemini-S/GMOSGemini-S/GMOS

Wavelength: 3800 – 5500 Å Wavelength: 3800 – 5500 Å 72 GCs with S/N > 30 72 GCs with S/N > 30

HδA HγA Hβ Mgb

Indicies & ModelsIndicies & Models

Metallicity

Age

Lick Lick (Burstein et al. 1984,

Worthey et al.1994, Trager et al.1998)

indices measured with indices measured with GONZOGONZO (Puzia et al. 2002, 2005)

Simple Stellar Population Simple Stellar Population

(SSP) Models(SSP) ModelsThomas, Maraston, & Bender (2003)Thomas, Maraston, & Korn (2004)

[[αα/Fe]/Fe] – can provide information – can provide information

on formation timescaleson formation timescales SNII – SNII – αα-elements – 100 Myr-elements – 100 Myr GCs in NGC 5128 SNIa – Fe elements – 1 GyrSNIa – Fe elements – 1 Gyr GCs in the Milky Way

Ages, [Z/H], and [Ages, [Z/H], and [αα /Fe] measured with a 3-D interpolation and /Fe] measured with a 3-D interpolation and ΧΧ22 minimization routineminimization routine 92% (23/25) of MP GCs are older than 8 Gyr 56% (26/47) of MR GCs are older than 8 Gyr 14% of GCs have ages 5-8 Gyr 18% of GCs have ages < 5 Gyr – all are MR [α /Fe] ~ 0-0.3, with of mean of 0.14 ± 0.04 – faster GC formation than in

recent major merger, but slower than GCs in dense environments GCs in Milky Way

GCs in NGC 5128

Previous studies by Peng et al. (2004) and Beasley et al. (2008)Previous studies by Peng et al. (2004) and Beasley et al. (2008) show similar show similar results.results.

Kinematics of the GC SystemKinematics of the GC SystemKinematics are a useful way to study properties of GC subpopulations Kinematics are a useful way to study properties of GC subpopulations

as well as obtain the mass of the host galaxyas well as obtain the mass of the host galaxy

Recent studies with GMOS, Recent studies with GMOS,

LDSS-2, VIMOS, Hydra – LDSS-2, VIMOS, Hydra –

189 new GCs189 new GCs Total: 605 GCs in NGC 5128, Total: 605 GCs in NGC 5128,

564 with radial velocities564 with radial velocities 268:271 MP:MR GCs268:271 MP:MR GCs

vvp p ­ projected radial velocity­ projected radial velocityvvsyssys ­ systemic velocity ­ systemic velocity ΩΩR ­ rotation amplitudeR ­ rotation amplitudeΘ ­ azimuthal angle­ azimuthal angleΘ

o o ­­ rotation axis rotation axis (Cote et al. 2001)

All

MR

MP

)sin( osysp Rvv Θ−ΘΩ+=

Rotation amplitude: Rotation amplitude: ΩR = 17± 14 km/s ΩR = 41± 15 km/s whole system

Θ o = 154 ± 47 ˚ E of N Θ o = 191 ± 18 ˚ E of N GCs > 8 Gyr

σ vp = 149 ± 3 km/s σ vp = 150 ± 3 km/s

Young GCs: Young GCs: ΩR = 58± 59 km/s Intermediate –aged GCs: Intermediate –aged GCs: ΩR = 53± 78 km/s

MR - mild rotation around the isophotal major axis and a decreasing velocity dispersion.MR - mild rotation around the isophotal major axis and a decreasing velocity dispersion.

MP - very mild rotation, but not around any axis, with a steady velocity dispersion.MP - very mild rotation, but not around any axis, with a steady velocity dispersion.

Kinematics of the GC SystemKinematics of the GC SystemMetal-poorMetal-poor Metal-richMetal-rich

ΩR = 17± 14 km/s ΩR = 41± 15 km/s whole system

Rotation Axis:Rotation Axis: Θ o = 154 ± 47 ˚ E of N Θ o = 191 ± 18 ˚ E of N GCs > 8 Gyr

σ vp = 149 ± 3 km/s σ vp = 150 ± 3 km/s

Young GCs: Young GCs: Θ o = 80 ± 84 ˚ E of N Intermediate –aged GCs: Intermediate –aged GCs: Θ o = 253 ± 54 ˚ E of N

MR - mild rotation around the isophotal major axis and a decreasing velocity dispersion.MR - mild rotation around the isophotal major axis and a decreasing velocity dispersion.

MP - very mild rotation, but not around any axis, with a steady velocity dispersion.MP - very mild rotation, but not around any axis, with a steady velocity dispersion.

Kinematics of the GC SystemKinematics of the GC SystemMetal-poorMetal-poor Metal-richMetal-rich

ΩR = 17± 14 km/s ΩR = 41± 15 km/s whole system

Θ o = 154 ± 47 ˚ E of N Θ o = 191 ± 18 ˚ E of N GCs > 8 Gyr

Velocity Dispersion:Velocity Dispersion: σ vp = 149 ± 3 km/s σ vp = 150 ± 3 km/s

MR - mild rotation around the isophotal major axis and a decreasing velocity dispersion.MR - mild rotation around the isophotal major axis and a decreasing velocity dispersion.

MP - very mild rotation, but not around any axis, with a steady velocity dispersion.MP - very mild rotation, but not around any axis, with a steady velocity dispersion.

Both MR and MP velocity dispersions tend to increase at larger radii.Both MR and MP velocity dispersions tend to increase at larger radii.

Kinematics of the GC SystemKinematics of the GC SystemMetal-poorMetal-poor Metal-richMetal-rich

Comparison to Planetary NebulaeComparison to Planetary Nebulae

Planetary nebulae are the Planetary nebulae are the most direct look at the most direct look at the kinematics of the field kinematics of the field starsstars

2 x 2 degree DSS image2 x 2 degree DSS image

Total 780 planetary Total 780 planetary nebulae confirmed by nebulae confirmed by radial velocity extending radial velocity extending out to 90 kpc out to 90 kpc (Hui et al. 1995, Peng et al. 2004)

Kinematics of the PNe SystemKinematics of the PNe System

Metal-richMetal-rich

Planetary Nebulae are rotating around Planetary Nebulae are rotating around

a similar axis to the MR GCs.a similar axis to the MR GCs.

Indicates the MR GCs follow theIndicates the MR GCs follow the

halo light of the galaxyhalo light of the galaxy

• interestingly, we find the MR GCs interestingly, we find the MR GCs

and the PNe also have the same and the PNe also have the same

radial surface density profile!radial surface density profile!• … … and MR GCs have similar and MR GCs have similar

metallicity to the halo field star metallicity to the halo field star

populationpopulation

PNe data whole MR GC system GCs > 8 Gyr

Rejkuba et al. 2005

Planetary Nebulae are rotating around Planetary Nebulae are rotating around

a similar axis to the MR GCs.a similar axis to the MR GCs.

Indicates the MR GCs follow theIndicates the MR GCs follow the

halo light of the galaxyhalo light of the galaxy

• interestingly, we find the MR GCs interestingly, we find the MR GCs

and the PNe also have the same and the PNe also have the same

radial surface density profile!radial surface density profile!• … … and MR GCs have similar and MR GCs have similar

metallicity to the halo field star metallicity to the halo field star

populationpopulation

Connection to Stellar HaloConnection to Stellar Halo

Mass Estimate of NGC 5128Mass Estimate of NGC 5128

GCs can be used as tracer objects to GCs can be used as tracer objects to

estimate the mass of NGC 5128estimate the mass of NGC 5128 Total mass = rotationally supported Total mass = rotationally supported

mass + pressure supported mass mass + pressure supported mass Spherical Jeans EquationSpherical Jeans Equation

Tracer Mass Estimator Tracer Mass Estimator (Evans et al. 2003)

M t = 5.5 ± 1.9 x 10 11 Msolar and M/L B = 15.3 Msolar/Lsolar (5’-20’)

M t = 11.7 ± 3.9 x 10 11 Msolar and M/L B = 32.5 Msolar/Lsolar (5’-43’)

All GCs (from 5’) MR GCs (5’-20’, 5’-40’) MP GCs (5’-20’, 5’-43’)

GvR

M outr

2max=

∑=

−=N

iisysifp Rvv

GNC

M1

2, )(

Ages, Metals, and KinematicsAges, Metals, and Kinematics

Numerical SimulationsNumerical Simulations Bekki et al. (2005) derived predictions for GC kinematics from galaxy Bekki et al. (2005) derived predictions for GC kinematics from galaxy

merging models. merging models. • Dissipationless merging of spiral galaxies with pre-existing MP and MR GCs Dissipationless merging of spiral galaxies with pre-existing MP and MR GCs • General results: General results:

• Major merger:Major merger:• velocity dispersions are generally flat or decliningvelocity dispersions are generally flat or declining• both MP and MR GCs show significant rotation in the outer regionsboth MP and MR GCs show significant rotation in the outer regions• kinematic misalignments with the galaxykinematic misalignments with the galaxy

• Minor merger: Minor merger: • velocity dispersions are generally flat or declining but are steepervelocity dispersions are generally flat or declining but are steeper• both MP and MR GCs can show rotation, but does not increase with both MP and MR GCs can show rotation, but does not increase with

distancedistance• kinematic misalignments with the galaxykinematic misalignments with the galaxy

NGC 5128:NGC 5128: Flat/decreasing velocity dispersion which rises with radius – anisotropy?Flat/decreasing velocity dispersion which rises with radius – anisotropy? Little rotation that does not increase with radiusLittle rotation that does not increase with radius Kinematic misalignmentsKinematic misalignments

Structural ParametersStructural Parameters

Structural parameters Structural parameters can provide information can provide information on the formation on the formation conditions of GCsconditions of GCs

Baade/IMACS imageBaade/IMACS image 25 fields (1.2 deg25 fields (1.2 deg22)) Taken in 0.45 arcsec Taken in 0.45 arcsec seeingseeing High resolution images High resolution images

in B, Rin B, R Accurate astrometry, Accurate astrometry,

photometry, GC photometry, GC candidates, candidates,

structural parametersstructural parameters

Structural Parameters of GCsStructural Parameters of GCs

ISHAPE ISHAPE (Larsen 1999, 2001)

SPs for 572 GCs out SPs for 572 GCs out to 8 Rto 8 Reffeff

Half light radii, rHalf light radii, reffeff : :

remains fairly constant remains fairly constant throughout GC lifetime throughout GC lifetime (Spitzer & Thaun 1972, Aarseth & Heggie 1998)

red GCs are typically red GCs are typically 17-30% smaller than 17-30% smaller than blue GCs blue GCs

(eg. Kundu & Whitmore, 1998)

Structural Parameters of GCsStructural Parameters of GCs

<1 R<1 Reffeff, red GCs were 30% smaller than blue GCs , red GCs were 30% smaller than blue GCs (also Harris 2009)

>1 R>1 Reffeff, negligible difference between the sizes of the two populations , negligible difference between the sizes of the two populations (also Spitler et al. 2006)

Possible explanations:Possible explanations:•Projection effect caused by r ~ (RProjection effect caused by r ~ (Rgcgc ) )0.50.5 (Larsen & Brodie 2003)

•Intrinsic differences of mass segregation and metallicity dependent stellar Intrinsic differences of mass segregation and metallicity dependent stellar lifetimes lifetimes (Jordan 2004)•GCs formed in shallower potential wells could be extended GCs formed in shallower potential wells could be extended (see Georgiev et al. 2008,2009)

ConclusionsConclusions

Globular Clusters in NGC 5128: Currently have 605 confirmed GCs in NGC 5128 and over 560 have

radial velocities Formation history:

Both MR and MP GCs are coeval and old forming the bulk of the galaxy Trend towards higher metallicities for younger ages

Formation timescales and ages do not suggest a recent gas-rich major merger, but rather formation through hierarchical merging with accretion and star–forming events in more recent times

Kinematics of GCs: GC system is dispersion dominated – does not suggest a disk-disk major

merger Mild rotation for the MR GCs around the major axis – same axis as the PNe (Very) mild rotation for the MP GCs around no axis

Mass of NGC 5128 estimated to be 5.5 ± 1.9 x 10 11 Msolar out to 20’

Structural Parameters of GCs: Half-light radii of the MR GCs are ~30% smaller than MP GCs within

~2 Reff of the galaxy only