Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://www.atnf.csiro.au/research/cena/documents/presentations/woodley.pdf Äàòà èçìåíåíèÿ: Thu Jul 16 04:36:29 2009 Äàòà èíäåêñèðîâàíèÿ: Fri Nov 27 08:37:30 2009 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: m 43

The Globular Cluster System of NGC 5128: Ages, Metallicities, Kinematics and Structural P ar a met er s
Kristin A. Woodley McMaster University, Canada
William Harris MatÌas GÑmez Thomas Puzia Gretchen Harris Doug Geisler McMaster University Universidad Andres Bello Herzberg Institute of Astrophysics University of Waterloo Universidad de ConcepciÑn


Outline


Globular Clusters (GCs) GC system ­ constraining the formation of NGC 5128




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









Summary


Globular Clusters (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 earlytype galaxies Multi-object spectrographs ­ ages, chemical compositions, radial velocity measurements


The GC System of NGC 5128




Estimated ~1500-2500 GCs (Harris et al. 2006) N = 605 GCs 268 are metal-poor 271 are metal-rich R < 45 arcmin

MP MR No photometry

Radial Velocity Studies:
1 2 3 4 5 6 7 8 9 1 . . . . . . . . . 0

van den Bergh et al. (1981) Hesser et al. (1984) Hesser et al. (1986) Harris et al. (1992) Peng et al. (2004) Woodley et al. (2005) Rejkuba et al. (2007) Beasley et al. (2008) Woodley et al. (2009a) . Woodley et al. (2009b)

Resolved GC Study:
1. Harris et al. (2006)


Ages and Metallicities of GCs
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

H

A

H

A

H

Mgb


Indicies & Models


L ick

(Burstein et al. 1984,

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

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


Me ta l lic it y

Simple Stellar Population (SSP) Models
e Ag
Thomas, Maraston, & Bender (2003) Thomas, Maraston, & Korn (2004)



[/Fe] ­ can provide information
on formation timescales


SNII ­ -elements ­ 100 Myr SNIa ­ Fe elements ­ 1 Gyr

GCs in NGC 5128 G C s i n th e M i l k y W a y


Ages, [Z/H], and [ /Fe] measured with a 3-D interpolation and 2 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 [ /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


Kinematics of the GC System
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 Total: 605 GCs in NGC 5128, 564 with radial velocities 268:271 MP:MR GCs

All

vp = v

sys

+ R sin( - o )

MP

vp projected radial velocity vsys systemic velocity R rotation amplitude azimuthal angle o rotation axis (Cote et al. 2001)

MR


Kinematics of the GC System
Metal-poor Metal-rich

Rotation amplitude: R = 17± 14 km/s
system o = 154 ± 47 ° E of N
vp

R = 41± 15 km/s o = 191 ± 18 ° E of N
vp

whole GCs > 8 Gyr

= 149 ± 3 km/s

= 150 ± 3 km/s

Young GCs: R = 58± 59 km/s

Intermediate ­aged GCs: R = 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.


Kinematics of the GC System
Metal-poor Metal-rich

R = 17± 14 km/s system

R = 41± 15 km/s o = 191 ± 18 ° E of N
vp

whole GCs > 8 Gyr

Rotation Axis: o = 154 ± 47 ° E of N

vp

= 149 ± 3 km/s

= 150 ± 3 km/s

Young GCs: o = 80 ± 84 ° E of N Intermediate ­aged GCs: 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.


Kinematics of the GC System
Metal-poor Metal-rich

R = 17± 14 km/s system o = 154 ± 47 ° E of N

R = 41± 15 km/s o = 191 ± 18 ° E of N
vp

whole GCs > 8 Gyr

Velocity Dispersion: vp = 149 ± 3 km/s

= 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.


Comparison to Planetary Nebulae



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)






Kinematics of the PNe System
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

P N e d a ta

whole MR GC system G C s > 8 G yr


Connection to Stellar Halo
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


Mass Estimate of NGC 5128






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

Rout v Mr = G


2 max

Tracer Mass Estimator (Evans et al. 2003)

C Mp = GN


i =1

N

(v

f ,i

- vsys ) 2 Ri
and M/L B = 15.3 Msolar/L
solar

M t = 5.5 ± 1.9 x 10

11

Mso

lar l ar

(5'-20') (5'-43')

M t = 11.7 ± 3.9 x 10

11

Mso

and M/L B = 32.5 Msolar/L

solar

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


Ages, Metals, and Kinematics


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 d i st a n ce · 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


Structural Parameters
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



Structural Parameters of GCs
ISHAPE (Larsen 1999, 2001) SPs for 572 GCs out t o 8 Re f f 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)


Structural Parameters of GCs

<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:

·Projection effect caused by r ~ (Rgc )0.5 (Larsen ·Intrinsic differences of mass segregation and lifetimes (Jordan 2004) ·GCs formed in shallower potential wells could

& Brodie 2003)

metallicity dependent stellar be extended (see Georgiev et al.


Conclusions


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 star­forming events in more recent times GC system is dispersion dominated ­ does not suggest a disk-disk major merger




Kinematics of GCs:


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

M

solar

out to 20'



Structural Parameters of GCs:


Half-light radii of the MR GCs are ~30% smaller than MP GCs within ~2 R of the galaxy only