Globular Clusters: HST Breathes New Life into Old Fossils Hubble Science Briefing Jay Anderson STScI June 3,

Outline Globular Clusters Omega Cen Early release images –Colors –Simulations Stellar Populations The cutting edge with HST 2

Globular Clusters “Textbook” simple stellar populations –Formed stars early –Single cloud, single metallicity, single age –Not large enough to self-enrich –Continue orbiting in spheroid of Galaxy Perfect laboratories to evaluate stellar evolution 3

OMEGA CEN EARLY-RELEASE IMAGE History of this image 1) Why taken? 2) Why ERO? 3) Why “saturated” ? 4

Familiar digital cameras: all at once Hubble: one Filter at a time James Webb ST: two at a time 5

10x10 ACS Early Release Field Central Field 6

The central field… RGBRGB 7.1

The central field… Blue 7.2

The central field… Red 7.3

The central field… RGBRGB 7.4

HUBBLE IMAX: MAYA was used to render the scene in 3-D 8

Decomposing the image… “a point source has no hair” Real close upwide view The PSF 9.1

Decomposing the image… “a point source has no hair” Simulated close upwide view The PSF 9.2

What Astronomers see… 10.1

What Astronomers see… 10.2

What Astronomers see… 10.3

What Astronomers see… 10.4

What Astronomers see… 10.5

What Astronomers see… 10.6

What Astronomers see… 10.7

What Astronomers see… 10.8

What Astronomers see… 10.9

What Astronomers see… 10.10

What Astronomers see… 10.11

10.12 What Astronomers see…

10.13

What Astronomers see… 1) Main Sequence 2) SubGiant Branch 3) Red Giant Branch 4) Horizontal Branch 5) White Dwarf Sequence 10.14

Easy to identify stars… RGB WDs SGB HB MSTO Red Dwarfs BSs 11

More metals More Helium Age Red Giant Branch A B C Globular clusters have traditionally been defined as textbook “simple” stellar populations: bound clusters of stars at the same distance, with the same age, and the same metallicity.  same small cloud Stellar Populations “Isochrone”12

Omega N T Omega CenNGC Tuc Extra sequences 13

Globular Cluster or Dwarf Spheroidal? Cambridge, UK

Stellar Populations More metals More Helium Age Inversion! More metals metal poor intermediate metal rich Red Giant Branch Similar to galaxies… 15

Could the textbook globular cluster not be one? 47Tuc N2808 N6656 N6388 OmCen ® Pluto Is Omega Cen a GC? 16

Is Omega Cen a globular? Are there any globular clusters? Questions to answer: 1)How do clusters enrich themselves? 2)Why are they all so different? 3)Is it all clusters, or just heavy ones? 4)What connection is there between clusters and galaxies? 5) Any relevance for star formation going on today? NGC2808 NGC

More HST with Clusters… HST’s advantages 1)Resolution: separate stars 2)Lower background: concentrate star, not sky 3)Stability: no atmosphere, same PSF 4)UV and IR coverage Proper motions: 1) Cluster-field separation 2) Search for black holes 18

The first full CMD Richer et al observed NGC6397 with 126 orbits –Discoveries End of WD cooling seq Blue hook at bottom! End of MS? –Limitations: field stars Blue Faint Bright Red HBL? WDCS 19

Proper-Motion Cleaning PI-Rich, UCLA 20.1

Proper-Motion Cleaning PI-Rich, UCLA 20.2

Proper-Motion Cleaning PI-Rich, UCLA 20.3

Proper-Motion Cleaning PI-Rich, UCLA 20.4

Intermediate-Mass Black Holes (IMBHs) in GCs BHs known to exist with –~10 M SUN : HMXBs –~10 6 M SUN : SMBHs at centers of galaxies –~10 4 M SUN : IMBHs? Could help explain how SMBHs grow ULXs in other galaxies M  relation… 10,000 M SUN ~20 km/s Greene & Ho (2006) 21

IMBHs in Globular Clusters II Several ways to find (PMs or RVs) –Fast moving star in orbit (smoking gun) –Rise in velocities at center –Also pulsars, accretion signatures, certain cusps Several ways to not find –Not enough stars/gas to sample its environs –Nearby stars all dark, ejecting binaries Easiest places to look: –Clusters with cusps & slow velocities Zone of influence r BH ~ M BH /  2 Omega Cen is not the easiest place to look… Yet… 22

Detections/limits in the literature –M15: back and forth; currently not required… –NGC6752: negative P pulsars: 1000 M SUN –47 Tuc: upper limit of 1500 M SUN –G1 in M31? X/Radio emission and velocities  Cen circumstantial evidence: –Noyola, Gebhardt & Bergmann 2008 (NGB08) 1) Detected a brightness cusp at center in ACS images 2) Used an IFU at Gemini and saw a velocity spike there Could be explained by a 40,000 M SUN IMBH This dispersion increase should be detectable with HST PMs… Current evidence? 23

Measuring Proper Motions Epoch1: 2002Epoch2:

Stars with good measured motions 25

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1026.

PM Profile Total motions of the 1000 stars in the inner 10  100 stars/bin Motions at the center are consistent with those at 10  (we also checked the NGB08 center…) Proper Motions indicate no interesting mass concentration at the center. Certainly not 40,000 M SUN ; at most 12,000 M SUN 27

Future Directions… Omega Cen –More stars? Better models? Other clusters coming! NGC 362 M15 NGC 6624 NGC 7099 NGC 6681 AND MORE! 28

THANK YOU! Watch for –Movies of Omega Cen motions –Movies of the CMD-morph 29