TheThe GlobularGlobular ClusterCluster SystemSystem ofof NGCNGC 5128:5128: Ages,Ages, Metallicities,Metallicities, KinematicsKinematics andand StructuralStructural ParametersParameters

Kristin A. Woodley McMaster University, Canada William Harris McMaster University Matías Gómez Universidad Andres Bello Thomas Puzia Herzberg Institute of Astrophysics Gretchen Harris University of Waterloo Doug Geisler Universidad de Concepción OutlineOutline  GlobularGlobular ClustersClusters (GCs)(GCs)

 GCGC systemsystem –– constrainingconstraining thethe formationformation ofof NGCNGC 51285128

 Ages, metallicities, and formation timescales of GCs

 Kinematics of the red and blue GCs

 GCs as tracers of mass

 Structural Parameters of the red and blue GCs

 SummarySummary GlobularGlobular ClustersClusters (GCs)(GCs)

 GCs are tracers of star formation episodes in their host galaxy  Formation of massive star clusters in interacting and starbursting galaxies (Whitmore & Schweizer 1995)

 Advantages:  Coeval structures  Large GC systems in early- type galaxies  Multi-object spectrographs – ages, chemical compositions, radial velocity measurements TheThe GCGC SystemSystem ofof NGCNGC 51285128

 Estimated ~1500-2500 GCs MP (Harris et al. 2006) MR  N = 605 GCs No photometry  268 are metal-poor  271 are metal-rich  R < 45 arcmin

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: 1. Harris et al. (2006) AgesAges andand MetallicitiesMetallicities ofof GCsGCs

Age and metallicity distribution functions can provide information of when GCs of different metallicity form

 Integrated light of GCs  Gemini-S/GMOS  Wavelength: 3800 – 5500 Å  72 GCs with S/N > 30

HδA HγA Hβ Mgb IndiciesIndicies && ModelsModels

 Lick (Burstein et al. 1984, Worthey et al.1994, Trager et al.1998) Metallicity indices measured with GONZO (Puzia et al. 2002, 2005)

 Simple Stellar Population (SSP) Models (SSP) Models Age Thomas, Maraston, & Bender (2003) Thomas, Maraston, & Korn (2004)

 [α/Fe] – can provide information on formation timescales  SNII – α-elements – 100 Myr GCs in NGC 5128  SNIa – Fe elements – 1 Gyr GCs in the Milky Way Ages, [Z/H], and [α /Fe] measured with a 3-D interpolation and Χ2 minimization 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) show similar results. KinematicsKinematics ofof thethe GCGC SystemSystem

Kinematics are a useful way to study properties of GC subpopulations as well as obtain the mass of the host galaxy

 Recent studies with GMOS, LDSS-2, VIMOS, Hydra – 189 new GCs All  Total: 605 GCs in NGC 5128, 564 with radial velocities  268:271 MP:MR GCs = + Ω Θ − Θ MP v p vsys Rsin( o ) vp ­ projected radial velocity vsys ­ systemic velocity ΩR ­ rotation amplitude Θ MR ­ azimuthal angle Θ o ­ rotation axis (Cote et al. 2001) KinematicsKinematics ofof thethe GCGC SystemSystem

Metal-poor Metal-rich

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

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. KinematicsKinematics ofof thethe GCGC SystemSystem

Metal-poor Metal-rich

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

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

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. KinematicsKinematics ofof thethe GCGC SystemSystem

Metal-poor Metal-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: 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. 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. ComparisonComparison toto PlanetaryPlanetary NebulaeNebulae

 Planetary nebulae are the most direct look at the kinematics of the field stars

 2 x 2 degree DSS image

 Total 780 planetary nebulae confirmed by radial velocity extending out to 90 kpc (Hui et al. 1995, Peng et al. 2004) KinematicsKinematics ofof thethe PNePNe SystemSystem

Metal-rich

Planetary Nebulae are rotating around a similar axis to the MR GCs.

Indicates the MR GCs follow the halo light of the galaxy

• interestingly, we find the MR GCs and the PNe also have the same radial surface density profile! • … and MR GCs have similar metallicity to the halo field star population

PNe data whole MR GC system GCs > 8 Gyr ConnectionConnection toto StellarStellar HaloHalo

Planetary Nebulae are rotating around a similar axis to the MR GCs.

Indicates the MR GCs follow the halo light of the galaxy

• interestingly, we find the MR GCs and the PNe also have the same radial surface density profile! • … and MR GCs have similar metallicity to the halo field star population

Rejkuba et al. 2005 MassMass EstimateEstimate ofof NGCNGC 51285128

 GCs can be used as tracer objects to estimate the mass of NGC 5128  Total mass = rotationally supported mass + pressure supported mass  Spherical Jeans Equation R v2 M = out max r G  Tracer Mass Estimator (Evans et al. 2003) N = C − 2 M p ∑(v f ,i vsys ) Ri GN i=1

11 M t = 5.5 ± 1.9 x 10 Msolar and M/L B = 15.3 Msolar/Lsolar (5’-20’) All GCs (from 5’) 11 MR GCs (5’-20’, 5’-40’) M t = 11.7 ± 3.9 x 10 Msolar and M/L B = 32.5 Msolar/Lsolar (5’-43’) MP GCs (5’-20’, 5’-43’) Ages,Ages, Metals,Metals, andand KinematicsKinematics

 Numerical Simulations  Bekki et al. (2005) derived predictions for GC kinematics from galaxy merging models. • Dissipationless merging of spiral galaxies with pre-existing MP and MR GCs • General results: • Major merger: • velocity dispersions are generally flat or declining • both MP and MR GCs show significant rotation in the outer regions • kinematic misalignments with the galaxy • Minor merger: • velocity dispersions are generally flat or declining but are steeper • both MP and MR GCs can show rotation, but does not increase with distance • kinematic misalignments with the galaxy

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

Structural parameters can provide information on the formation conditions of GCs

Baade/IMACS image  25 fields (1.2 deg2)  Taken in 0.45 arcsec seeing  High resolution images in B, R  Accurate astrometry, photometry, GC candidates, structural parameters StructuralStructural ParametersParameters ofof GCsGCs

ISHAPE (Larsen 1999, 2001)

SPs for 572 GCs out to 8 Reff

Half light radii, reff :

. remains fairly constant throughout GC lifetime (Spitzer & Thaun 1972, Aarseth & Heggie 1998) . red GCs are typically 17-30% smaller than blue GCs (eg. Kundu & Whitmore, 1998) StructuralStructural ParametersParameters ofof GCsGCs

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

>1 Reff, negligible difference between the sizes of the two populations (also Spitler et al. 2006) Possible explanations: 0.5 •Projection effect caused by r ~ (Rgc ) (Larsen & Brodie 2003) •Intrinsic differences of mass segregation and metallicity dependent stellar lifetimes (Jordan 2004) •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  11 Mass of NGC 5128 estimated to be 5.5 ± 1.9 x 10 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