The Globular Cluster System The Globular Cluster System of NGC 5128: Ages, Metallicities, of NGC 5128: Ages, Metallicities, Kinematics and Structural Kinematics and Structural Parameters Parameters Kristin A. Woodley Kristin A. Woodley McMaster University, Canada McMaster University, Canada William Harris William Harris McMaster University McMaster University Matías Gómez Matías Gómez Universidad Andres Bello Universidad Andres Bello Thomas Puzia Thomas Puzia Herzberg Institute of Astrophysics Herzberg Institute of Astrophysics Gretchen Harris Gretchen Harris University of Waterloo University of Waterloo Doug Geisler Doug Geisler Universidad de Concepción Universidad de Concepción
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The Globular Cluster System of NGC 5128: Ages ... · of NGC 5128: Ages, Metallicities, Kinematics and Structural Parameters ... Estimated ~1500-2500 GCs (Harris et al ... Harris et
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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
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
[[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
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
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’)
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,
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